Related
I have two forms, one is the main form and the other is an options form. So say for example that the user clicks on my menu on the main form: Tools -> Options, this would cause my options form to be shown.
My question is how can I send data from my options form back to my main form? I know I could use properties, but I have a lot of options and this seems like an tedious odd thing to do.
So what is the best way?
Form1 triggers Form2 to open. Form2 has overloaded constructor which takes calling form as argument and provides its reference to Form2 members. This solves the communication problem. For example I've exposed Label Property as public in Form1 which is modified in Form2.
With this approach you can do communication in different ways.
Download Link for Sample Project
//Your Form1
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Form2 frm = new Form2(this);
frm.Show();
}
public string LabelText
{
get { return Lbl.Text; }
set { Lbl.Text = value; }
}
}
//Your Form2
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}
private Form1 mainForm = null;
public Form2(Form callingForm)
{
mainForm = callingForm as Form1;
InitializeComponent();
}
private void Form2_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
this.mainForm.LabelText = txtMessage.Text;
}
}
(source: ruchitsurati.net)
(source: ruchitsurati.net)
In the comments to the accepted answer, Neeraj Gulia writes:
This leads to tight coupling of the forms Form1 and Form2, I guess instead one should use custom events for such kind of scenarios.
The comment is exactly right. The accepted answer is not bad; for simple programs, and especially for people just learning programming and trying to get basic scenarios to work, it's a very useful example of how a pair of forms can interact.
However, it's true that the coupling that example causes can and should be avoided, and that in the particular example, an event would accomplish the same thing in a general-purpose, decoupled way.
Here's an example, using the accepted answer's code as the baseline:
Form1.cs:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Form2 frm = new Form2();
frm.Button1Click += (s1, e1) => Lbl.Text = ((Form2)s1).Message;
frm.Show();
}
}
The above code creates a new instance of Form2, and then before showing it, adds an event handler to that form's Button1Click event.
Note that the expression (s1, e1) => Lbl.Text = ((Form2)s1).Message is converted automatically by the compiler to a method that looks something similar to (but definitely not exactly like) this:
private void frm_Message(object s1, EventArgs e1)
{
Lbl.Text = ((Form2)s1).Message;
}
There are actually lots of ways/syntaxes to implement and subscribe the event handler. For example, using an anonymous method as the above, you don't really need to cast the sender parameter; instead you can just use the frm local variable directly: (s1, e1) => Lbl.Text = frm.Message.
Going the other way, you don't need to use an anonymous method. You could in fact just declare a regular method just like the compiler-generated one I show above, and then subscribe that method to the event: frm.Button1Click += frm_Message; (where you have of course used the name frm_Message for the method, just as in my example above).
Regardless of how you do it, of course you will need for Form2 to actually implement that Button1Click event. That's very simple…
Form2.cs:
public partial class Form2 : Form
{
public event EventHandler Button1Click;
public string Message { get { return txtMessage.Text; } }
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
EventHandler handler = Button1Click;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
In addition to the event, I've also declared a property Message that exposes the Text property (and only the Text property, and only as read-only in fact) of the txtMessage control. This allows the subscriber to the event to get the value and do whatever it needs to with it.
Note that all that the event does is to alert the subscriber that the button has in fact been clicked. It's up to the subscriber to decide how to interpret or react to that event (e.g. by retrieving the value of the Message property and assigning it to something).
Alternatively, you could in fact deliver the text along with the event itself, by declaring a new EventArgs sub-class and using that for the event instead:
public class MessageEventArgs : EventArgs
{
public string Message { get; private set; }
public MessageEventArgs(string message)
{
Message = message;
}
}
public partial class Form2 : Form
{
public event EventHandler<MessageEventArgs> Button1Click;
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
EventHandler handler = Button1Click;
if (handler != null)
{
handler(this, new MessageEventArgs(txtMessage.Text));
}
}
}
Then the subscriber can just retrieve the message value directly from the event object:
frm.Button1Click += (sender, e) => Lbl.Text = e.Message;
The important thing note in all of the above variations is that at no point does the class Form2 need to know anything about Form1. Having Form1 know about Form2 is unavoidable; after all, that's the object that will create a new Form2 instance and use it. But the relationship can be asymmetrical, with Form2 being usable by any object that needs the features it offers. By exposing the functionality as an event (and optionally with a property), it makes itself useful without limiting its usefulness to only the Form1 class.
The best in this case would be to have some OptionsService class/interface that is accessible via IServiceProvider.
Just add an event when something changes, and the rest of the app can respond to it.
There are lots of ways to perform communication between two Forms.
Some of them have already been explained to you. I am showing you the other way around.
Assuming you have to update some settings from the child form to the parent form. You can make use of these two ways as well :
Using System.Action (Here you simply pass the main forms function as the parameter to the child form like a callback function)
OpenForms Method ( You directly call one of your open forms)
Using System.Action
You can think of it as a callback function passed to the child form.
// -------- IN THE MAIN FORM --------
// CALLING THE CHILD FORM IN YOUR CODE LOOKS LIKE THIS
Options frmOptions = new Options(UpdateSettings);
frmOptions.Show();
// YOUR FUNCTION IN THE MAIN FORM TO BE EXECUTED
public void UpdateSettings(string data)
{
// DO YOUR STUFF HERE
}
// -------- IN THE CHILD FORM --------
Action<string> UpdateSettings = null;
// IN THE CHILD FORMS CONSTRUCTOR
public Options(Action<string> UpdateSettings)
{
InitializeComponent();
this.UpdateSettings = UpdateSettings;
}
private void btnUpdate_Click(object sender, EventArgs e)
{
// CALLING THE CALLBACK FUNCTION
if (UpdateSettings != null)
UpdateSettings("some data");
}
OpenForms Method
This method is easy (2 lines). But only works with forms that are open.
All you need to do is add these two lines where ever you want to pass some data.
Main frmMain = (Main)Application.OpenForms["Main"];
frmMain.UpdateSettings("Some data");
Properties is one option, shared static class - another option, events - another option...
You might try AutoMapper. Keep your options in a separate class and then use AutoMapper to shuttle the data between the class and the form.
Create a Class and put all your properties inside the class .. Create a Property in the parent class and set it from your child (options) form
You can have a function in Form B like so:
public SettingsResults GetNewSettings()
{
if(this.ShowDialog() == DialogResult.Ok)
{
return new SettingsResult { ... };
}
else
{
return null;
}
}
And you can call it like this:
...
using(var fb = new FormB())
{
var s = fb.GetNewSettings();
...
// Notify other parts of the application that settings have changed.
}
MVC, MVP, MVVM -- slight overkill for someone admittedly saying they want tutorials. Those are theories that have entire courses dedicated to them.
As already posted, passing an object around is probably easiest. If treating a class as an object (interchangeable in this sense) is new, then you may want to spend another 2-4 weeks figuring out properties and constructors and such.
I'm not a C# master by any means, but these concepts need to be pretty concrete if you want to go much further beyond passing values between two forms (also classes/objects in their own right). Not trying to be mean here at all, it just sounds like you're moving from something like VB6 (or any language with globals) to something far more structured.
Eventually, it will click.
This is probably sidestepping your problem a little bit, but my settings dialog uses the Application Settings construct. http://msdn.microsoft.com/en-us/library/k4s6c3a0.aspx
I can't find a good example that's similar to how I do it (which is actually having an actual class+object), but this covers another way of doing it:
Reading default application settings in C#
A form is a class, just like any other class. Add some public variables to your form class and set them when they click the button to close the form (technically they are just hiding it).
A VB.NET example, but you'll get the idea -
In your OptionsForm class:
Public Option1 as String = ""
etc. Set them when they hit the "Ok" button.
So in your main form, when they hit the "options" button - you create your options form:
OptionsForm.ShowDialog()
when it exits, you harvest your option settings from the public variables on the form:
option1 = OptionsForm.Option1
etc.
The best way to deal with communication between containers is to implement an observer class
The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.
(Wikipedia)
the way i do this is creating an Observer class, and inside it write something like this:
1 public delegate void dlFuncToBeImplemented(string signal);
2 public static event dlFuncToBeImplemented OnFuncToBeImplemented;
3 public static void FuncToBeImplemented(string signal)
4 {
5 OnFuncToBeImplemented(signal);
6 }
so basically: the first line says that there would be a function that somebody else will implement
the second line is creating an event that occurs when the delegated function will call
and the third line is the creation of the function that calls the event
so in your UserControl, you should add a function like this:
private void ObserverRegister()//will contain all observer function registration
{
Observer.OnFuncToBeImplemented += Observer_OnFuncToBeImplemented;
/*and more observer function registration............*/
}
void Observer_OnFuncToBeImplemented(string signal)//the function that will occur when FuncToBeImplemented(signal) will call
{
MessageBox.Show("Signal "+signal+" received!", "Atention!", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
}
and in your Form you should do something like:
public static int signal = 0;
public void button1_Click(object sender, EventArgs e)
{
Observer.FuncToBeImplemented(signal);//will call the event in the user control
}
and now, you can register this function to a whole bunch of other controls and containers and they will all get the signal
I hope this would help :)
This may sound stupid, But I am having hard time to figure this out; any help would be appreciated:
I have two user controls called “Safety_Check” and “OEE_Track”. In my MainForm I have a panel called “pnl_main_controller” this is where I am displaying both my user controls. I have two buttons on my main form and I am dynamically switching between both without any issue.
Safety_Check User control;
public partial class Safety_Check : UserControl
{
private static Safety_Check _instance;
public static Safety_Check instance
{
get
{
if (_instance == null)
_instance = new Safety_Check();
return _instance;
}
}
public Safety_Check()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
///////------------------------
}
}
OEE_Track User control
public partial class OEE_Track : UserControl
{
private static OEE_Track _instance;
public static OEE_Track instance
{
get
{
if (_instance == null)
_instance = new OEE_Track();
return _instance;
}
}
public OEE_Track()
{
InitializeComponent();
}
}
MainForm:
public partial class MainForm : Form
{
private void btn_reg_Click(object sender, EventArgs e)
{
if (!pnl_main_controller.Contains(Safety_Check.instance))
{
pnl_main_controller.Controls.Add(Safety_Check.instance);
Safety_Check.instance.Dock = DockStyle.Fill;
Safety_Check.instance.BringToFront();
}
else
{
Safety_Check.instance.BringToFront();
} }
private void btn_OEE_Click(object sender, EventArgs e)
{
if (!pnl_main_controller.Contains(OEE_Track.instance))
{
pnl_main_controller.Controls.Add(OEE_Track.instance);
OEE_Track.instance.Dock = DockStyle.Fill;
OEE_Track.instance.BringToFront();
}
else
{
OEE_Track.instance.BringToFront();
}
}
What I am trying to do is I have a button called “Button1” on my “Safety_Check” Usercontrol, whenever I press this , I want “Safety_Check” to be disappear on “pnl_main_controller” and bring “OEE_Track” to the panel
There are several solutions for interaction between controls. Controls are classes and like any other class they can interact with each other using their public properties and methods or using some mediator.
In this case, your controls don't need to know each other and don't need to interact to each other directly:
They can ask another object which knows both controls, to do the job for them.
Or they can raise their request notification and the one who subscribed to that notification, will serve it.
To ask another object to do the job for them you have multiple solutions. As an example you can implement a specific interface in the parent form and in the child controls, cast the parent to that specific interface and call a specific method which do the job for you.
For raising the request notification, an easy solution is relying on events. You can create an event in the child control and raise it when you need the parent do something for you. Then in the parent subscribe to that event and do the job.
Example - Using event
I assume you have UserControl1 having Button1 inside and you have handled Click event of Button1. Then you can create Button1Clicked event and raise it when Button1 clicked:
public event EventHandler Button1Clicked;
private void Button1_Click(object sender, EventArgs e)
{
Button1Clicked?.Invoke(this, e);
}
Then in the parent form, subscribe for the event and do whatever you want:
private void userControl11_Button1Clicked(object sender, EventArgs e)
{
//Hide userControl11 and show userControl21
}
Example - Using interface
I assume, you have an interface having a few standard methods:
public interface IDoSomething
{
void DoSomething();
void DoSomethingElse();
}
And you have implemented the interface in your parent form:
public class Form1: Form, IDoSomething
{
// ...
public void DoSomething()
{
//Hide userControl11 and show userControl21
}
public void DoSomethingElse()
{
// ...
}
}
Then in you user control:
private void Button1_Click(object sender, EventArgs e)
{
var f = FindForm() as IDoSomething;
if(f!=null)
f.DoSomething();
}
I want to expand on Reza Aghaei's answer a bit. I think it could get even better than it is now.
First way to do this
If I were you I would have some interface ICheckedView which has at least 1 method to implement like so:
ICheckedView
{
void Continue();
}
Now, we're able to apply this interface to any class in our solution, most likely to views, though. Next, I would make your main form implement this interface and implement the required method. The in this case we want our main form to remove the control from the panel and add a new control. Frankly, our Safety check control doesn't need to (and maybe shouldn't) know about other controls or what happens next. It's just used for flow of control.
Finally, you need to add either a public property, or maybe even a parameter to the constructor for Safety_Check which includes an ICheckedView in it. When your safety check control gets clicked it can tell whoever has been passed into it (we'll say the client) that it must continue.
Second way to do this
It can be done with an action delegate.
If you add an Action delegate to your safety check, you could just pop in any method whose signature matches that delegate (void methodName()). The constructor for your Safety_Check control should include an Action and that Action would get assigned to a private field of the class. Then when it's time to invoke, that action can be invoked directly.
Notes on this method
Because we're probably invoking from the UI thread in the first place, we're probably alright, but you need to think about thread safety here. The invoke required pattern can help you around this.
I have two forms, one is the main form and the other is an options form. So say for example that the user clicks on my menu on the main form: Tools -> Options, this would cause my options form to be shown.
My question is how can I send data from my options form back to my main form? I know I could use properties, but I have a lot of options and this seems like an tedious odd thing to do.
So what is the best way?
Form1 triggers Form2 to open. Form2 has overloaded constructor which takes calling form as argument and provides its reference to Form2 members. This solves the communication problem. For example I've exposed Label Property as public in Form1 which is modified in Form2.
With this approach you can do communication in different ways.
Download Link for Sample Project
//Your Form1
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Form2 frm = new Form2(this);
frm.Show();
}
public string LabelText
{
get { return Lbl.Text; }
set { Lbl.Text = value; }
}
}
//Your Form2
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}
private Form1 mainForm = null;
public Form2(Form callingForm)
{
mainForm = callingForm as Form1;
InitializeComponent();
}
private void Form2_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
this.mainForm.LabelText = txtMessage.Text;
}
}
(source: ruchitsurati.net)
(source: ruchitsurati.net)
In the comments to the accepted answer, Neeraj Gulia writes:
This leads to tight coupling of the forms Form1 and Form2, I guess instead one should use custom events for such kind of scenarios.
The comment is exactly right. The accepted answer is not bad; for simple programs, and especially for people just learning programming and trying to get basic scenarios to work, it's a very useful example of how a pair of forms can interact.
However, it's true that the coupling that example causes can and should be avoided, and that in the particular example, an event would accomplish the same thing in a general-purpose, decoupled way.
Here's an example, using the accepted answer's code as the baseline:
Form1.cs:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Form2 frm = new Form2();
frm.Button1Click += (s1, e1) => Lbl.Text = ((Form2)s1).Message;
frm.Show();
}
}
The above code creates a new instance of Form2, and then before showing it, adds an event handler to that form's Button1Click event.
Note that the expression (s1, e1) => Lbl.Text = ((Form2)s1).Message is converted automatically by the compiler to a method that looks something similar to (but definitely not exactly like) this:
private void frm_Message(object s1, EventArgs e1)
{
Lbl.Text = ((Form2)s1).Message;
}
There are actually lots of ways/syntaxes to implement and subscribe the event handler. For example, using an anonymous method as the above, you don't really need to cast the sender parameter; instead you can just use the frm local variable directly: (s1, e1) => Lbl.Text = frm.Message.
Going the other way, you don't need to use an anonymous method. You could in fact just declare a regular method just like the compiler-generated one I show above, and then subscribe that method to the event: frm.Button1Click += frm_Message; (where you have of course used the name frm_Message for the method, just as in my example above).
Regardless of how you do it, of course you will need for Form2 to actually implement that Button1Click event. That's very simple…
Form2.cs:
public partial class Form2 : Form
{
public event EventHandler Button1Click;
public string Message { get { return txtMessage.Text; } }
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
EventHandler handler = Button1Click;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
In addition to the event, I've also declared a property Message that exposes the Text property (and only the Text property, and only as read-only in fact) of the txtMessage control. This allows the subscriber to the event to get the value and do whatever it needs to with it.
Note that all that the event does is to alert the subscriber that the button has in fact been clicked. It's up to the subscriber to decide how to interpret or react to that event (e.g. by retrieving the value of the Message property and assigning it to something).
Alternatively, you could in fact deliver the text along with the event itself, by declaring a new EventArgs sub-class and using that for the event instead:
public class MessageEventArgs : EventArgs
{
public string Message { get; private set; }
public MessageEventArgs(string message)
{
Message = message;
}
}
public partial class Form2 : Form
{
public event EventHandler<MessageEventArgs> Button1Click;
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
EventHandler handler = Button1Click;
if (handler != null)
{
handler(this, new MessageEventArgs(txtMessage.Text));
}
}
}
Then the subscriber can just retrieve the message value directly from the event object:
frm.Button1Click += (sender, e) => Lbl.Text = e.Message;
The important thing note in all of the above variations is that at no point does the class Form2 need to know anything about Form1. Having Form1 know about Form2 is unavoidable; after all, that's the object that will create a new Form2 instance and use it. But the relationship can be asymmetrical, with Form2 being usable by any object that needs the features it offers. By exposing the functionality as an event (and optionally with a property), it makes itself useful without limiting its usefulness to only the Form1 class.
The best in this case would be to have some OptionsService class/interface that is accessible via IServiceProvider.
Just add an event when something changes, and the rest of the app can respond to it.
There are lots of ways to perform communication between two Forms.
Some of them have already been explained to you. I am showing you the other way around.
Assuming you have to update some settings from the child form to the parent form. You can make use of these two ways as well :
Using System.Action (Here you simply pass the main forms function as the parameter to the child form like a callback function)
OpenForms Method ( You directly call one of your open forms)
Using System.Action
You can think of it as a callback function passed to the child form.
// -------- IN THE MAIN FORM --------
// CALLING THE CHILD FORM IN YOUR CODE LOOKS LIKE THIS
Options frmOptions = new Options(UpdateSettings);
frmOptions.Show();
// YOUR FUNCTION IN THE MAIN FORM TO BE EXECUTED
public void UpdateSettings(string data)
{
// DO YOUR STUFF HERE
}
// -------- IN THE CHILD FORM --------
Action<string> UpdateSettings = null;
// IN THE CHILD FORMS CONSTRUCTOR
public Options(Action<string> UpdateSettings)
{
InitializeComponent();
this.UpdateSettings = UpdateSettings;
}
private void btnUpdate_Click(object sender, EventArgs e)
{
// CALLING THE CALLBACK FUNCTION
if (UpdateSettings != null)
UpdateSettings("some data");
}
OpenForms Method
This method is easy (2 lines). But only works with forms that are open.
All you need to do is add these two lines where ever you want to pass some data.
Main frmMain = (Main)Application.OpenForms["Main"];
frmMain.UpdateSettings("Some data");
Properties is one option, shared static class - another option, events - another option...
You might try AutoMapper. Keep your options in a separate class and then use AutoMapper to shuttle the data between the class and the form.
Create a Class and put all your properties inside the class .. Create a Property in the parent class and set it from your child (options) form
You can have a function in Form B like so:
public SettingsResults GetNewSettings()
{
if(this.ShowDialog() == DialogResult.Ok)
{
return new SettingsResult { ... };
}
else
{
return null;
}
}
And you can call it like this:
...
using(var fb = new FormB())
{
var s = fb.GetNewSettings();
...
// Notify other parts of the application that settings have changed.
}
MVC, MVP, MVVM -- slight overkill for someone admittedly saying they want tutorials. Those are theories that have entire courses dedicated to them.
As already posted, passing an object around is probably easiest. If treating a class as an object (interchangeable in this sense) is new, then you may want to spend another 2-4 weeks figuring out properties and constructors and such.
I'm not a C# master by any means, but these concepts need to be pretty concrete if you want to go much further beyond passing values between two forms (also classes/objects in their own right). Not trying to be mean here at all, it just sounds like you're moving from something like VB6 (or any language with globals) to something far more structured.
Eventually, it will click.
This is probably sidestepping your problem a little bit, but my settings dialog uses the Application Settings construct. http://msdn.microsoft.com/en-us/library/k4s6c3a0.aspx
I can't find a good example that's similar to how I do it (which is actually having an actual class+object), but this covers another way of doing it:
Reading default application settings in C#
A form is a class, just like any other class. Add some public variables to your form class and set them when they click the button to close the form (technically they are just hiding it).
A VB.NET example, but you'll get the idea -
In your OptionsForm class:
Public Option1 as String = ""
etc. Set them when they hit the "Ok" button.
So in your main form, when they hit the "options" button - you create your options form:
OptionsForm.ShowDialog()
when it exits, you harvest your option settings from the public variables on the form:
option1 = OptionsForm.Option1
etc.
The best way to deal with communication between containers is to implement an observer class
The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.
(Wikipedia)
the way i do this is creating an Observer class, and inside it write something like this:
1 public delegate void dlFuncToBeImplemented(string signal);
2 public static event dlFuncToBeImplemented OnFuncToBeImplemented;
3 public static void FuncToBeImplemented(string signal)
4 {
5 OnFuncToBeImplemented(signal);
6 }
so basically: the first line says that there would be a function that somebody else will implement
the second line is creating an event that occurs when the delegated function will call
and the third line is the creation of the function that calls the event
so in your UserControl, you should add a function like this:
private void ObserverRegister()//will contain all observer function registration
{
Observer.OnFuncToBeImplemented += Observer_OnFuncToBeImplemented;
/*and more observer function registration............*/
}
void Observer_OnFuncToBeImplemented(string signal)//the function that will occur when FuncToBeImplemented(signal) will call
{
MessageBox.Show("Signal "+signal+" received!", "Atention!", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
}
and in your Form you should do something like:
public static int signal = 0;
public void button1_Click(object sender, EventArgs e)
{
Observer.FuncToBeImplemented(signal);//will call the event in the user control
}
and now, you can register this function to a whole bunch of other controls and containers and they will all get the signal
I hope this would help :)
I have a static generic class that helps me move events around with very little overhead:
public static class MessageBus<T> where T : EventArgs
{
public static event EventHandler<T> MessageReceived;
public static void SendMessage(object sender, T message)
{
if (MessageReceived != null)
MessageReceived(sender, message);
}
}
To create a system-wide message bus, I simply need to define an EventArgs class to pass around any arbitrary bits of information:
class MyEventArgs : EventArgs
{
public string Message { get; set; }
}
Anywhere I'm interested in this event, I just wire up a handler:
MessageBus<MyEventArgs>.MessageReceived += (s,e) => DoSomething();
Likewise, triggering the event is just as easy:
MessageBus<MyEventArgs>.SendMessage(this, new MyEventArgs() {Message="hi mom"});
Using MessageBus and a custom EventArgs class lets me have an application wide message sink for a specific type of message. This comes in handy when you have several forms that, for example, display customer information and maybe a couple forms that update that information. None of the forms know about each other and none of them need to be wired to a static "super class".
I have a couple questions:
fxCop complains about using static methods with generics, but this is exactly what I'm after here. I want there to be exactly one MessageBus for each type of message handled. Using a static with a generic saves me from writing all the code that would maintain the list of MessageBus objects.
Are the listening objects being kept "alive" via the MessageReceived event?
For instance, perhaps I have this code in a Form.Load event:
MessageBus<CustomerChangedEventArgs>.MessageReceived += (s,e) => DoReload();
When the Form is Closed, is the Form being retained in memory because MessageReceived has a reference to its DoReload method? Should I be removing the reference when the form closes:
MessageBus<CustomerChangedEventArgs>.MessageReceived -= (s,e) => DoReload();
Well, yes, you should, but if you use the lambda syntax as you've done in your example I think it won't work (by which I mean, the handler will not be de-registered successfully).
Someone correct me if I'm wrong, but I believe this is true because using the lambda syntax effectively creates a new EventHandler<CustomerChangedEventArgs> object, with its own place in memory. When you try to remove this handler, using the lambda syntax again, this creates yet another new EventHandler<CustomerChangedEventArgs> object, which is not equal to the first one you created; and so the first one never gets de-registered.
Sadly, I think you'll need to actually define a method like this:
DoReload(object sender, CustomerChangedEventArgs e) {
DoReload(); // your original overload, which doesn't actually care
// about the sender and e parameters
}
This way you can do:
MessageBus<CustomerChangedEventArgs>.MessageReceived += DoReload;
And later:
MessageBus<CustomerChangedEventArgs>.MessageReceived -= DoReload;
Yes, there are problems. Your event handlers will cause the form object to stay referenced, you have to explicitly unregister the event handlers. The lambdas make this impossible, you'll have to write an explicit handler.
This pattern has a name, "Event Broker service". It is part of the Composite UI Application Block, published by Microsoft's Pattern and Practices team. Beg, borrow and steal (if not use) what you can from this.
You could use weak references to store the event handlers. That way, unhooked handlers won't prevent garbage collection of the objects.
public static class MessageBus<T> where T : EventArgs
{
private static List<WeakReference> _handlers = new List<WeakReference>();
public static event EventHandler<T> MessageReceived
{
add
{
_handlers.Add(new WeakReference(value));
}
remove
{
// also remove "dead" (garbage collected) handlers
_handlers.RemoveAll(wh => !wh.IsAlive || wh.Target.Equals(value));
}
}
public static void SendMessage(object sender, T message)
{
foreach(var weakHandler in _handlers)
{
if (weakHandler.IsAlive)
{
var handler = weakHandler.Target as EventHandler<T>;
handler(sender, message);
}
}
}
}
I have two forms, one is the main form and the other is an options form. So say for example that the user clicks on my menu on the main form: Tools -> Options, this would cause my options form to be shown.
My question is how can I send data from my options form back to my main form? I know I could use properties, but I have a lot of options and this seems like an tedious odd thing to do.
So what is the best way?
Form1 triggers Form2 to open. Form2 has overloaded constructor which takes calling form as argument and provides its reference to Form2 members. This solves the communication problem. For example I've exposed Label Property as public in Form1 which is modified in Form2.
With this approach you can do communication in different ways.
Download Link for Sample Project
//Your Form1
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Form2 frm = new Form2(this);
frm.Show();
}
public string LabelText
{
get { return Lbl.Text; }
set { Lbl.Text = value; }
}
}
//Your Form2
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}
private Form1 mainForm = null;
public Form2(Form callingForm)
{
mainForm = callingForm as Form1;
InitializeComponent();
}
private void Form2_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
this.mainForm.LabelText = txtMessage.Text;
}
}
(source: ruchitsurati.net)
(source: ruchitsurati.net)
In the comments to the accepted answer, Neeraj Gulia writes:
This leads to tight coupling of the forms Form1 and Form2, I guess instead one should use custom events for such kind of scenarios.
The comment is exactly right. The accepted answer is not bad; for simple programs, and especially for people just learning programming and trying to get basic scenarios to work, it's a very useful example of how a pair of forms can interact.
However, it's true that the coupling that example causes can and should be avoided, and that in the particular example, an event would accomplish the same thing in a general-purpose, decoupled way.
Here's an example, using the accepted answer's code as the baseline:
Form1.cs:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Form2 frm = new Form2();
frm.Button1Click += (s1, e1) => Lbl.Text = ((Form2)s1).Message;
frm.Show();
}
}
The above code creates a new instance of Form2, and then before showing it, adds an event handler to that form's Button1Click event.
Note that the expression (s1, e1) => Lbl.Text = ((Form2)s1).Message is converted automatically by the compiler to a method that looks something similar to (but definitely not exactly like) this:
private void frm_Message(object s1, EventArgs e1)
{
Lbl.Text = ((Form2)s1).Message;
}
There are actually lots of ways/syntaxes to implement and subscribe the event handler. For example, using an anonymous method as the above, you don't really need to cast the sender parameter; instead you can just use the frm local variable directly: (s1, e1) => Lbl.Text = frm.Message.
Going the other way, you don't need to use an anonymous method. You could in fact just declare a regular method just like the compiler-generated one I show above, and then subscribe that method to the event: frm.Button1Click += frm_Message; (where you have of course used the name frm_Message for the method, just as in my example above).
Regardless of how you do it, of course you will need for Form2 to actually implement that Button1Click event. That's very simple…
Form2.cs:
public partial class Form2 : Form
{
public event EventHandler Button1Click;
public string Message { get { return txtMessage.Text; } }
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
EventHandler handler = Button1Click;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
In addition to the event, I've also declared a property Message that exposes the Text property (and only the Text property, and only as read-only in fact) of the txtMessage control. This allows the subscriber to the event to get the value and do whatever it needs to with it.
Note that all that the event does is to alert the subscriber that the button has in fact been clicked. It's up to the subscriber to decide how to interpret or react to that event (e.g. by retrieving the value of the Message property and assigning it to something).
Alternatively, you could in fact deliver the text along with the event itself, by declaring a new EventArgs sub-class and using that for the event instead:
public class MessageEventArgs : EventArgs
{
public string Message { get; private set; }
public MessageEventArgs(string message)
{
Message = message;
}
}
public partial class Form2 : Form
{
public event EventHandler<MessageEventArgs> Button1Click;
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
EventHandler handler = Button1Click;
if (handler != null)
{
handler(this, new MessageEventArgs(txtMessage.Text));
}
}
}
Then the subscriber can just retrieve the message value directly from the event object:
frm.Button1Click += (sender, e) => Lbl.Text = e.Message;
The important thing note in all of the above variations is that at no point does the class Form2 need to know anything about Form1. Having Form1 know about Form2 is unavoidable; after all, that's the object that will create a new Form2 instance and use it. But the relationship can be asymmetrical, with Form2 being usable by any object that needs the features it offers. By exposing the functionality as an event (and optionally with a property), it makes itself useful without limiting its usefulness to only the Form1 class.
The best in this case would be to have some OptionsService class/interface that is accessible via IServiceProvider.
Just add an event when something changes, and the rest of the app can respond to it.
There are lots of ways to perform communication between two Forms.
Some of them have already been explained to you. I am showing you the other way around.
Assuming you have to update some settings from the child form to the parent form. You can make use of these two ways as well :
Using System.Action (Here you simply pass the main forms function as the parameter to the child form like a callback function)
OpenForms Method ( You directly call one of your open forms)
Using System.Action
You can think of it as a callback function passed to the child form.
// -------- IN THE MAIN FORM --------
// CALLING THE CHILD FORM IN YOUR CODE LOOKS LIKE THIS
Options frmOptions = new Options(UpdateSettings);
frmOptions.Show();
// YOUR FUNCTION IN THE MAIN FORM TO BE EXECUTED
public void UpdateSettings(string data)
{
// DO YOUR STUFF HERE
}
// -------- IN THE CHILD FORM --------
Action<string> UpdateSettings = null;
// IN THE CHILD FORMS CONSTRUCTOR
public Options(Action<string> UpdateSettings)
{
InitializeComponent();
this.UpdateSettings = UpdateSettings;
}
private void btnUpdate_Click(object sender, EventArgs e)
{
// CALLING THE CALLBACK FUNCTION
if (UpdateSettings != null)
UpdateSettings("some data");
}
OpenForms Method
This method is easy (2 lines). But only works with forms that are open.
All you need to do is add these two lines where ever you want to pass some data.
Main frmMain = (Main)Application.OpenForms["Main"];
frmMain.UpdateSettings("Some data");
Properties is one option, shared static class - another option, events - another option...
You might try AutoMapper. Keep your options in a separate class and then use AutoMapper to shuttle the data between the class and the form.
Create a Class and put all your properties inside the class .. Create a Property in the parent class and set it from your child (options) form
You can have a function in Form B like so:
public SettingsResults GetNewSettings()
{
if(this.ShowDialog() == DialogResult.Ok)
{
return new SettingsResult { ... };
}
else
{
return null;
}
}
And you can call it like this:
...
using(var fb = new FormB())
{
var s = fb.GetNewSettings();
...
// Notify other parts of the application that settings have changed.
}
MVC, MVP, MVVM -- slight overkill for someone admittedly saying they want tutorials. Those are theories that have entire courses dedicated to them.
As already posted, passing an object around is probably easiest. If treating a class as an object (interchangeable in this sense) is new, then you may want to spend another 2-4 weeks figuring out properties and constructors and such.
I'm not a C# master by any means, but these concepts need to be pretty concrete if you want to go much further beyond passing values between two forms (also classes/objects in their own right). Not trying to be mean here at all, it just sounds like you're moving from something like VB6 (or any language with globals) to something far more structured.
Eventually, it will click.
This is probably sidestepping your problem a little bit, but my settings dialog uses the Application Settings construct. http://msdn.microsoft.com/en-us/library/k4s6c3a0.aspx
I can't find a good example that's similar to how I do it (which is actually having an actual class+object), but this covers another way of doing it:
Reading default application settings in C#
A form is a class, just like any other class. Add some public variables to your form class and set them when they click the button to close the form (technically they are just hiding it).
A VB.NET example, but you'll get the idea -
In your OptionsForm class:
Public Option1 as String = ""
etc. Set them when they hit the "Ok" button.
So in your main form, when they hit the "options" button - you create your options form:
OptionsForm.ShowDialog()
when it exits, you harvest your option settings from the public variables on the form:
option1 = OptionsForm.Option1
etc.
The best way to deal with communication between containers is to implement an observer class
The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.
(Wikipedia)
the way i do this is creating an Observer class, and inside it write something like this:
1 public delegate void dlFuncToBeImplemented(string signal);
2 public static event dlFuncToBeImplemented OnFuncToBeImplemented;
3 public static void FuncToBeImplemented(string signal)
4 {
5 OnFuncToBeImplemented(signal);
6 }
so basically: the first line says that there would be a function that somebody else will implement
the second line is creating an event that occurs when the delegated function will call
and the third line is the creation of the function that calls the event
so in your UserControl, you should add a function like this:
private void ObserverRegister()//will contain all observer function registration
{
Observer.OnFuncToBeImplemented += Observer_OnFuncToBeImplemented;
/*and more observer function registration............*/
}
void Observer_OnFuncToBeImplemented(string signal)//the function that will occur when FuncToBeImplemented(signal) will call
{
MessageBox.Show("Signal "+signal+" received!", "Atention!", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
}
and in your Form you should do something like:
public static int signal = 0;
public void button1_Click(object sender, EventArgs e)
{
Observer.FuncToBeImplemented(signal);//will call the event in the user control
}
and now, you can register this function to a whole bunch of other controls and containers and they will all get the signal
I hope this would help :)