This can seems like a simple question ... the crux is how to match the button delegate signature void, object, eventargs with my method or use an event delegate.
As an example, I have code for a button that changes color when it's clicked. However,
button1.Click += new EventHandler(KK.ChangeColor);
carries the EventArgs from the button to the ChangeColor(object sender, EventArgs e) method, but is meaningless to the rest of the code which use ColorEventArgs; and
button1.Click += delegate(object sender, EventArgs e){ KK.ChangeColor(sender); };
doesn't allow for later removal of the delegate later in the code.
So which is better? Adding unnecessary parameters to all my methods to match the button delegate or suffering from not being able to remove the delegate later ?
or How would I change the delegate signature of the button? It seems there must be a 'cleaner' way to do this?
Will appreciate advice.
"It seems there must be a 'cleaner' way to do this?"
In my opinion, better design would depends on what exactly ChangeColor method do. If it is doing only specific operation that closely related to event button clicked, I would just leave it as the real event handler method. That means, it should have required parameters to match Button.Click event handler signature (I don't think there is option to "change the delegate signature") :
void ChangeColor(object sender, EventArgs e)
{
MessageBox.Show("Button {0} clicked!!!", ((Button)sender).Name);
}
Otherwise, if it is doing not only specific operation related to event button clicked, I would refactor codes unrelated to button click event to another method. This way, the other method doesn't need to have unnecessary parameters. For example :
void ChangeColor(object sender, EventArgs e)
{
var buttonName = ((Button)sender).Name;
MessageBox.Show("Button {0} clicked!!! Save form data", );
//assume that form name can be determined from name of button being clicked
SaveFormToDatabase(buttonName);
}
private void SaveFormToDatabase(string formName)
{
//save form specified in parameter
}
Related
i got this function on my form:
private void UpdateQuantityDataGridView(object sender, DataGridViewCellEventArgs e)
{
(...codes)
}
and i want to call that function inside another function, let's say when i click a "OK" button, this below function will run and execute above function that has parameter type.
private void button5_Click(object sender, EventArgs e) // This is the "OK" button click handler.
{
SubmitButton(sender, e);
}
private void SubmitButton(object sender, EventArgs e) // This is function of "OK" button
{
(...codes)
UpdateQuantityDataGridView("What should i put in here? I tried (sender, e), but it is useless")
}
I know that this function run when we put something like this:
dataGridView1.CellValueChanged += new DataGridViewSystemEventHandler(...);
But, i don't want that because that function will only run if the cell value in DataGridView has been changed, i want to access that function when i click "OK" button. But, what should i put inside a parameters value?
Extract the logic currently in the UpdateQuantityDataGridView() method and put it into a new public method named whatever you want, then you can call this logic from anywhere in your class or any other code that references your class, like this:
public void DoUpdateQuantityLogic()
{
// Put logic here
}
Note: If you do not actually use sender or e, then you can leave the method above without parameters, but if you do use e, for example, then you need to have a parameter for the DoUpdateQuantityLogic() method to account for what the property of the e object you are using is.
Now you can call DoUpdateQuantityLogic() from you other methods, like this:
private void button5_Click(object sender, EventArgs e) // This is the "OK" button click handler.
{
DoUpdateQuantityLogic();
}
private void SubmitButton(object sender, EventArgs e) // This is function of "OK" button
{
DoUpdateQuantityLogic();
}
This allows you to re-use your logic and also isolates the functionality into a method that makes unit testing easier, if you choose to unit test this logic.
If you are determined to use your existing event-based method infrastructure, then you can pass null for both the sender and the e arguments of the event handler, like this:
UpdateQuantityDataGridView(null, null);
If your method UpdateQuantityDataGridView() actually using the parameters sender and e? If not just pass null for both.
UpdateQuantityDataGridView(null, null);
If you are using them:
var e = new DataGridViewCellEventArgs();
// assign any properties
UpdateQuantityDataGridView(dataGridView1, e);
You can use sender, but you can't use e because UpdateQuantityDataGridView needs e to be of type DataGridViewCellEventArgs.
Depending on what your UpdateQuantityDataGridView handler wants to do with the e parameter, you could just pass null when you call it from your SubmitButton.
Otherwise, you'll have to new a DataGridViewCellEventArgs and populate it with the appropriate values your own handler requires/expects.
I just started programming, and I want to use WinForms to make multiple buttons that you can click on to change from white to lime-green and back to white. I have done this for one button:
private void button1_Click(object sender, EventArgs e)
{
if (button1.BackColor != Color.Lime)
{
button1.BackColor = Color.Lime;
}
else
{
button1.BackColor = Color.White;
}
}
Now I could copy and paste that for all of the buttons, but I know that is inefficient; and if I use winforms to reference button1 on button2, it will just change the color of button1 (obviously).
So, do I need to use a helper method, new class, or something else? What would that look like?
There are a couple of approaches. One might be to create a common function which the different buttons call:
private void button1_Click(object sender, EventArgs e)
{
ChangeColor(button1);
}
private void ChangeColor(Button button)
{
if (button.BackColor != Color.Lime)
button.BackColor = Color.Lime;
else
button.BackColor = Color.White;
}
Then each button handler can use that same function call.
Or, if all of these buttons will always ever do exactly the same thing, then you can use one click handler function for all of them. In this case what you'd need to do is determine which button invoked the handler (whereas you're currently referencing button1 directly) so that you know which one to change. The sender object passed into the handler function is actually a reference to the form element which invoked the handler. All you need to do is cast it:
private void button_Click(object sender, EventArgs e)
{
var button = (Button)sender;
if (button.BackColor != Color.Lime)
button.BackColor = Color.Lime;
else
button.BackColor = Color.White;
}
So first the handler grabs a reference to the button which invoked it, then runs the logic on that button. Note also how I made the name of the handler function slightly more generic. Now you'd go to the form designer and set button_Click as the click handler for all of the buttons which should invoke this.
You do this the exact same way you'd do it for any C# class. You derive your own class and customize the base class behavior. Every event has a corresponding OnXxxx() method that you can override.
Add a new class to your project and paste this code:
using System;
using System.Windows.Forms;
class MyButton : Button {
protected override void OnClick(EventArgs e) {
// Your code here
//...
base.OnClick(e);
}
}
Change the code in OnClick() to do what you want to do. Compile. You'll now have your own button control on the top of the toolbox. And can drop as many copies of it as you want on a form. They'll all behave the same without having to add any code in the form.
Probably the easiest way would be to have each button invoke the same click handler. Then inside of your handler use the Sender instead of hard coding Button1.
private void buttons_Click(object sender, EventArgs e)
{
var theButton = (Button) sender;
if (theButton.BackColor != Color.Lime)
{
theButton.BackColor = Color.Lime;
}
else
{
theButton.BackColor = Color.White;
}
}
You can get the button that raised the Click event by casting sender to Button.
You can then add the same handler to every button.
I'm a VB guy.... in VB.Net you can add multiple handlers for events and connect multiple events to the same handler.
This sub hooks all clicks to color the buttons.
Private Sub ColorButtons(sender As System.Object, e As System.EventArgs) _
Handles Button1.Click, Button2.Click, ..
I do this all the time accidentally because I drag/copy a control to make a new one and the new button gets added to the original's events.
Other Subs can handle the same events to do other work - both will execute.
No idea how to do this in C#.
The proper way to do this really is to associate each button's click event to the function you have coded for that purpose (you want the function to run when the button is clicked, right?), so add the following (or similar) to an appropriate section of your code:
MyButton1.Click += new RoutedEventHandler(buttons_Click);
MyButton2.Click += new RoutedEventHandler(buttons_Click);
etc...
You can associate as many controls to the event handler as you like.
What I usually do before is this:
private void button2_Click(object sender, EventArgs e)
{
button1.PerformClick();
}
This code will just simply run the codes under button1_Click.
But try not to practice as such and just simply put it in a function/method just like what David suggested.
If I have a button which does something and also a double-click event on a data grid which I want to do the same thing, what is the best way to ensure that only one function has to be maintained?
Apart from doing the following, is there any fancy C# way to indicate that two events are to do the same thing?
void button1_Click(...) { MyFunction(); }
void dataGrid1_DoubleClick(...) { MyFunction(); }
void MyFunction() { // do stuff }
I suppose that you are talking about a DataGridView (WinForms) so the signature of the event DoubleClick in the DataGridView and the signature of Click event on a button control is the same.
(An EventHadler). In this case you can simply set the same method using the form designer or manually bind the event
dataGridView1.DoubleClick += new EventHandler(MyFunction);
button1.Click += new EventHandler(MyFunction);
Of course the MyFunction method should match the expected signature of an EventHandler
private void MyFunction(object sender, EventArgs e)
{
// do your work
}
Reviewing my answer after a few minutes I wish to add:
If you find yourself in a situation in which you need to differentiate between the controls using the sender object (like Control c = sender as Control; if (c.Name == "someName") ) I really suggest you to return to the first idea. Call a common method but keep the EventHandler separated for each control involved.
Using VS, in the form's designer view You can set the procedure You want to call to each control's each event in the control's properties window.
image
Just to add to what Steve said, you will want to bind these events to your function manually in the Load event of your form, instead of using the events under the lightning bolt in the properties window in the designer, like so:
private void Form1_Load(object sender, EventArgs e)
{
button1.Click += MyMethod;
dataGridView1.DoubleClick += MyMethod;
}
void MyMethod(object sender, EventArgs e)
{
//Do Stuff
}
Also, declaring a new instance of the EventHandler class has been redundant since Anonymous methods were introduced to C#, you can just point the event directly at the method as shown above.
Assume that I have a WinFoms project. There is just one button (e.g. button1).
The question is: is it possible to trigger the ButtonClicked event via code without really clicking it?
Button controls have a PerformClick() method that you can call.
button1.PerformClick();
The .NET framework uses a pattern where for every event X there is a method protected void OnX(EventArgs e) {} that raises event X. See this Msdn article. To raise an event from outside the declaring class you will have to derive the class and add a public wrapper method. In the case of Button it would look like this:
class MyButton : System.Windows.Forms.Button
{
public void ProgrammaticClick(EventArgs e)
{
base.OnClick(e);
}
}
You can just call the event handler function directly and specify null for the sender and EventArgs.Empty for the arguments.
void ButtonClicked(object sender, EventArgs e)
{
// do stuff
}
// Somewhere else in your code:
button1.Click += new EventHandler(ButtonClicked);
// call the event handler directly:
ButtonClicked(button1, EventArgs.Empty);
Or, rather, you'd move the logic out of the ButtonClicked event into its own function, and then your event handler and the other code you have would in turn call the new function.
void StuffThatHappensOnButtonClick()
{
// do stuff
}
void ButtonClicked(object sender, EventArgs e)
{
StuffThatHappensOnButtonClick();
}
// Somewhere else in your code:
button1.Click += new EventHandler(ButtonClicked);
// Simulate the button click:
StuffThatHappensOnButtonClick();
The latter method has the advantage of letting you separate your business and UI logic. You really should never have any business logic in your control event handlers.
Yes, just call the method the way you would call any other. For example:
private void btnSayHello_Click(object sender, EventArgs e)
{
MessageBox.Show("Hello World!");
}
private void btnTriggerHello_Click(object sender, EventArgs e)
{
btnSayHello_Click(null, null);
}
button1.PerformClick();
But if you have to do something like this maybe it's better to move the code you have under the event on a new method ?
Why don't you just put your event code into a Method. Then have the Event execute the method. This way if you need to execute the same code that the Event rises, you can, but simply just calling the "Method".
void Event_Method()
{
//Put Event code here.
MessageBox.Show("Hello!");
}
void _btnSend_Click(object sender, EventArgs e)
{
Event_Method();
}
void AnotherMethod()
{
Event_Method();
}
Make sense? Now the "Click" event AND anywhere in code you can trigger the same code as the "Click" event.
Don't trigger the event, call the method that the event calls. ;)
In most cases you would not need to do that. Simply wrap your functionality in functions related to a specific purpose (task). You call this function inside your event and anywhere else it's needed.
Overthink your approach.
I recently had this problem where I wanted to programatically click a button that had multiple event handlers assigned to it (think UserControl or derived classes).
For example:
myButton.Click += ButtonClicked1
myButton.Click += ButtonClicked2;
void ButtonClicked1(object sender, EventArgs e)
{
Console.WriteLine("ButtonClicked1");
}
void ButtonClicked2(object sender, EventArgs e)
{
Console.WriteLine("ButtonClicked1");
}
When you click the button, both functions will get called. In the instances where you want to programmatically fire an event handler for a function from a form (for example, when a user presses enter in a Text field then call the InvokeOnClick method passing through the control you. For example
this.InvokeOnClick(myButton, EventArgs.Empty);
Where this is the Form instance you are in.
use a for loop to call the button_click event
private void btnadd_Click(object sender, RoutedEventArgs e)
{
for (int i = 0; i <= 2; i++)
StuffThatHappensOnButtonClick();
}
void StuffThatHappensOnButtonClick()
{
........do stuff
}
we assume at least one time you need click the button
I created a Windows Application with a form and few buttons on it. I need to fire the button click event automatically some times based on the parameter value passed to the application.
static class SensexPrediction
{
static void Main(string[] Args) <---- Modified this so accepting arguments.
{
Application.Run(new Sensex_Prediction_Form(Args)); <--- Passing Args to Form.
}
}
Below is the Code for Sensex_Prediction_Form method.
public Sensex_Prediction_Form(String[] Args)
{
InitializeComponent();
if (Args.Length != 0) //There is atleast one argument.
{
this.Invoker = Args[0]; <-----Invoker is the name of the data member of the class.
}
}
Now on form load if Invoker == "X" i need to perform button1_Click event code. For that i wrote the following...
private void Sensex_Prediction_Form_Load(object sender, EventArgs e)
{
if(Inovker == "x")
{
predict_butn.performclick();
}
}
But click is not happening automatically even though argument passed is X.
What i couldn't understand is the button name in the solution explorer is predict_butn but when i click on the button the event code is in a function named button1_click. Is this the reason?
Please help. Thanks.
After the suggestions i separated the event code and actual logic in a separate method named prediction.
private void Sensex_Prediction_Form_Load(object sender, EventArgs e)
{
if (Invoker == "Scheduler")
{
prediction();
}
}
And i initialized the data variable of the class with Scheduler as below..
public string Invoker = "Scheduler";
Even then when i load the form the method is not being invoked.
As suggested i corrected the connection between button name and even method name etc.
thank q
Suprisingly..(for me :-))
if (Invoker == "Scheduler")
{
MessageBox.Show("Testing");
prediction();
MessageBox.Show("OK");
}
Testing message is getting executed but after that it just displays the form. so what could be the reason?
Understood the issue..I am getting an exception object reference not set..because i have a line that says
ActiveForm.Text = "Sensex Prediction System ";
At this point form has not been loaded so it can't set the text.
------> Now the issue is how to call a method automatically after loading the form? because the method will have code that will modify the form while executing.
Got it...using the "shown" event for the form able to do what i wanted. Thanks.
Promote the code within button1_click to a method. Then once the form is loaded and if the parameter match your filter, call the method.
private void Button1_Click(object sender, EventArgs e)
{
DoSomething();
}
private void Sensex_Prediction_Form_Load(object sender, EventArgs e)
{
if(Inovker == "X")
{
DoSomething();
}
}
private void DoSomething()
{
...
}
Extract the code out of the button event into it's own method that is called in the button click. Now you just need to call that new extracted method instead of trying to invoke a ui button click.
First you can use Environment.GetCommandLineArgs() instead of passing the args to the constructor of the form.
Second you may assign the wrong event handler to the click. reassign the predict_butn.Click to its correct event handler instead of the current one which is button1_click
Double click button to generate event handler(for example button1_Click(object sender, System.EventArgs e)), and then you want to trigger that method just call button1_Click(null, null)
Of course better solution is to create one function with your logic and then call that function in button click event and when Invoker == "X".
First of all, you're not checking whether Invoker == 'X', but Invoker == 'x'. This may be part of the problem. Comparing strings with == is not good practice, however. You should use
if (Invoker.Equals('X', StringComparison.InvariantCulture))
Is the action performed if you click the button with your mouse? If so, the problem is not the event handler.
If it is not performed, the event handler and the button's event are not connected. You can check in the button's properties whether the event handler is attached to the button's click event.
What happens if you double-click the button in the designer? Is a new event handler created? If so, move the code from button1_click to the new event handler and delete the button1_click event handler.
Event handlers and control events are not automatically associated. You need to do this in the control's properties.