I am used to writing embedded c and poorly skilled in c#.
My problem is that I want to be able to run the function openAnotherForm() from Welcome_Form and right now the code does not work. I patiently tried different things but only managed to push my frustration.
I simplified my relevant code to illustrate the problem.
File 1 - This will run and open file 2.
class UIcode
{
private Welcome_Form Welcome;
private AnotherForm_Form AnotherForm;
public UIcode()
{
Welcome = new Welcome_Form();
Application.Run(Welcome);
}
public void openAnotherForm()
{
Welcome.Hide();
AnotherForm = new AnotherForm_Form();
AnotherForm.ShowDialog();
}
}
File 2 - When I click TheButton, the program should run the function openAnotherFrom from file 1.
public partial class Welcome_Form : Form
{
public Welcome_Form()
{
InitializeComponent();
}
private void TheButton_Click(object sender, EventArgs e)
{
// Function from file 1
UIcode.openAnotherForm();
}
}
I realize the problem might be quite trivial but I would still be grateful for an explanation on how to do this.
Preferable: The functions from UIcode should only be recognized by classes specified by UIcode.
You can change the constructor to take a reference to the instance of UIcode that opened it:
private static UIcode myParent;
public Welcome_Form(UIcode parent)
{
myParent = parent;
InitializeComponent();
}
Now in UIcode:
public UIcode()
{
Welcome = new Welcome_Form(this);
Application.Run(Welcome);
}
And finally, back in Welcome_Form:
private void TheButton_Click(object sender, EventArgs e)
{
// Function from file 1
myParent.openAnotherForm();
}
Your openAnotherForm() method is not static, so it needs an instance reference in order to be used. Either instantiate a UICode object, or mark the method as static.
You to create an instance of the class in File1 to call the method. You've called the class UICode, so the constructor should be renamed from public UserInterface() to public UICode().
class UIcode
{
private Welcome_Form Welcome;
private AnotherForm_Form AnotherForm;
public UIcode() // Renamed Constructor
{
Welcome = new Welcome_Form();
Application.Run(Welcome);
}
public void openAnotherForm()
{
Welcome.Hide();
AnotherForm = new AnotherForm_Form();
AnotherForm.ShowDialog();
}
}
public partial class Welcome_Form : Form
{
public Welcome_Form()
{
InitializeComponent();
}
private void TheButton_Click(object sender, EventArgs e)
{
// Create an instance UICode
UICode instance = new UICode();
// Call the method from the instance, not from the class.
instance.openAnotherForm();
}
}
Alternatively, you can make openAnotherForm() a static method, but you'll also need to make the instance variables (Welcome and AnotherForm) static. You will also need to initialize them, but you can do that by making the constructor static as well.
class UIcode
{
private static Welcome_Form Welcome;
private static AnotherForm_Form AnotherForm;
public static UIcode() // Renamed Constructor
{
Welcome = new Welcome_Form();
Application.Run(Welcome);
}
public static void openAnotherForm()
{
Welcome.Hide();
AnotherForm = new AnotherForm_Form();
AnotherForm.ShowDialog();
}
}
Related
So I roughly got this:
public partial class Form1 : Form
{
GameEngine engine;
public Form1()
{
engine = new GameEngine();
}
public void repaint()
{
}
}
class GameEngine
{
public void update()
{
}
}
Now i wanna add something to the update() method, which makes it call the repaint() method, inside of that instance of the Form1 class, in which the respective object of the GameEngine class was created.
In java i could've done it like this
engine = new GameEngine()
{
public void repaintCaller()
{
repaint();
}
};
and call repaintCaller() in the update() method, but that doesn't work in c#, now what is the equilvalent way to do this in c#?
One way to have it is:
public partial class Form1 : Form
{
GameEngine engine;
public Form1()
{
engine = new GameEngine();
engine.update(this);
}
public void repaint()
{
}
}
class GameEngine
{
public void update(Form1 form)
{
form.repaint();
}
}
You could pass to the GameEngine.update method an Action delegate to the repaint method in the form instance
public partial class Form1 : Form
{
GameEngine engine;
public Form1()
{
engine = new GameEngine();
// I put the call here for demo purpose,
// of course you call the engine.update
// method when you need and where you want
engine.update(repaint)
}
public void repaint()
{
Console.WriteLine("repaint called in the Form1 instance");
}
}
class GameEngine
{
public void update(Action clientUpdate)
{
if(clientUpdate != null)
clientUpdate.Invoke();
// or just... clientUpdate();
}
}
The parameterless Action delegate in C# is a way to pass, as parameter, a method (repaint) to the called method (update). Of course, you could pass the whole Form1 instance to the update but this approach binds the GameEngine class to the Form1 class. With the Action approach you are free from this coupling and you could pass any other method that returns void and doesn't take any parameter defined in any class of your program. This frees your GameEngine.update method from any specific bind to the caller.
I would try something like that
class GameEngine
{
public void update(ref Form1 caller)
{
caller.Refresh() //msdn says "Forces the control to invalidate its client area and immediately redraw itself and any child controls."
}
}
public partial class Form1 : Form
{
[...]
engine = new GameEngine()
engine.update(ref This)
}
I'm not sure of anything, i'm not used to C#.
I just hope it will help a bit :)
You can also set Events from your form, like this:
public partial class Form1 : Form
{
GameEngine engine;
public Form1()
{
InitializeComponent();
engine = new GameEngine();
engine.repaintRequired += engine_repaintRequired;
engine.update();
}
private void engine_repaintRequired(object sender, EventArgs e)
{
repaint();
}
public void repaint()
{
Console.Write("repaint");
}
}
class GameEngine
{
public event EventHandler repaintRequired;
public void update()
{
onRepaintRequired();
}
private void onRepaintRequired()
{
if (repaintRequired != null)
repaintRequired(this, new EventArgs());
}
}
i'm learning how to use custom events in c#, but i get some errors
i get "An object reference is required for the nonstatic field, method, or property" in the bold words
so i tried following this
but case 1 couldn't be tried 'cause TypeChanged is already a nonstatic method (i think)
in case 2 i get "impossible to acces BicycleType as an instance reference, qualify it as a type"
public class Bicycle
{
public event EventHandler TypeChanged;
private string type;
...
public string BicycleType {
get { return this.type; }
set {
this.type = value;
if (this.TypeChanged != null)
this.TypeChanged( this, new EventArgs() );
}
}
public Bicycle() {}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("heila!");
Bicycle istanza = new Bicycle();
istanza.TypeChanged += new EventHandler(**istanza_TypeChanged**);
istanza.BicycleType = "io";
Console.WriteLine("io");
}
void istanza_TypeChanged(object sender, EventArgs e) {
Console.WriteLine("rofkd");
}
}
the tutorial i followed told me i can use events "as" methods, maybe i'm wrong here?
the code is completely similar to te tutorial code
sorry for my bad english and thanks in advance
As you are registering the event from the main method, which is static, the event handler (istanza_TypeChanged) has to be made static too.
You problem is that Main is static and can therefore not access nonstatic members of the class Program. However you try to access istanza_TypeChanged. That is what is causing your exception.
You have to make istanza_TypeChanged static too to solve the issue
class Program
{
static void Main(string[] args)
{
Console.WriteLine("heila!");
Bicycle istanza = new Bicycle();
istanza.TypeChanged += new EventHandler(**istanza_TypeChanged**);
istanza.BicycleType = "io";
Console.WriteLine("io");
}
static void istanza_TypeChanged(object sender, EventArgs e)
{
Console.WriteLine("rofkd");
}
}
Register the event from a non-static context or change your event to be static.
Change istanza_TypeChanged to the following:
private static void istanza_TypeChanged(object sender, EventArgs e)
{
Console.WriteLine("rofkd");
}
The following fired the event for me:
public class Bicycle
{
public event EventHandler TypeChanged;
private string type;
public string BicycleType
{
get { return this.type; }
set
{
this.type = value;
if (this.TypeChanged != null)
this.TypeChanged(this, new EventArgs());
}
}
public Bicycle()
{
}
private class Program
{
private static void Main(string[] args)
{
Console.WriteLine("heila!");
Bicycle istanza = new Bicycle();
istanza.TypeChanged += istanza_TypeChanged;
istanza.BicycleType = "io";
Console.WriteLine("io");
}
private static void istanza_TypeChanged(object sender, EventArgs e)
{
Console.WriteLine("rofkd");
}
}
}
I think I couldnt do this thing, but I try to ask (maybe :)).
Suppose I have this Main class :
public class UiUtils
{
public static MyObject myObject;
public UiUtils()
{
myObject=new MyObject();
}
}
now if I want to try to call this instance from another Context Class (web application), I do this :
public partial class context_eventi_CustomClass : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
Console.Write(UiUtils.myObject.Title());
}
}
but what I'd like to do is this :
public partial class context_eventi_CustomClass : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
Console.Write(myObject.Title());
}
}
so, use directly myObject and not UiUtils.myObject :)
I think this is not possible, but maybe I wrong and there are any strategies :) Thanks
** EDIT **
my solution for the moment :
public class UiUtils
{
public static MyObject myObject;
public UiUtils()
{
myObject=new MyObject();
iContext.myObject = myObject;
}
}
public class iContext : System.Web.UI.UserControl
{
public static MyObject myObject;
public iContext()
{
}
public iContext(MyObject myObject)
{
myObject = myObject;
}
}
public partial class context_eventi_CustomClass : iContext
{
protected void Page_Load(object sender, EventArgs e)
{
Console.Write(myObject.Title());
}
}
seems to works! What do you think about?
Per MSDN,
A static method, field, property, or
event is callable on a class even when
no instance of the class has been
created. If any instances of the class
are created, they cannot be used to
access the static member. Only one
copy of static fields and events
exists, and static methods and
properties can only access static
fields and static events. Static
members are often used to represent
data or calculations that do not
change in response to object state.
and
"To access a static class member, use the name of the class instead of a variable name to specify the location of the member."
and
The static member is always accessed
by the class name, not the
instance name
#Daniel Earwicker says in his answer on SO here:
...Static members fail to integrate
well with inheritance. It makes no
sense to have them heritable. So I
keep static things in separate static
classes...
So I am not clear on your design why MyObject needs to be static. All you are trying to save is a little typing, but inheritance will not help you here either.
Edit:
I tried to replicate your code in a simple console application. The output is not what you would expect:
namespace ConsoleApplication1
{
public class UiUtils
{
public static int myObject = 1;
public UiUtils()
{
myObject = new int();
iContext.myObject = myObject;
Console.WriteLine("This is UiUtils\n");
}
}
public class iContext
{
public static int myObject = 2;
public iContext()
{
Console.WriteLine("This is iContext\n");
}
public iContext(int myObject)
{
myObject = myObject;
}
}
public class iContext2 : iContext
{
public static int myObject = 3;
public iContext2()
{
Console.WriteLine(myObject.ToString() + "\nThis is iContext2\n");
Console.WriteLine(iContext.myObject.ToString());
}
}
class Program
{
static void Main(string[] args)
{
iContext2 icontext = new iContext2();
Console.In.ReadLine();
}
}
}
The output ends up being this:
This is iContext
3
This is iContext2
If you add a call to iContext.myObject, then it outputs it's number:
This is iContext
3
This is iContext2
2
To access the object without typing the class you can use inheritance.
public class CustomClass : UiUtils
This will share UiUtils properties with CustomClass
I hope that the title and this simple example says everything.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public void UpdateLabel(string str)
{
label1.Text = str;
MessageBox.Show("Hello");
}
private void buttonIn_Click(object sender, EventArgs e)
{
UpdateLabel("inside");
}
private void buttonOut_Click(object sender, EventArgs e)
{
MyClass Outside = new MyClass();
Outside.MyMethod();
}
}
public class MyClass
{
public void MyMethod()
{
Form1 MyForm1 = new Form1();
MyForm1.UpdateLabel("outside");
}
}
When I'm trying to change lable1 from MyClass it does nothing. But I can get to the UpdateLable method from outside, it says Hello to me, it just doesn't change the label.
Use a delegate for setting your label
public class MyClass {
Action<String> labelSetter;
public MyClass(Action<String> labelSetter) {
this.labelSetter = labelSetter;
}
public void MyMethod() {
labelSetter("outside");
}
}
.
public void buttonOut_Click(object sender, EventArgs e) {
var outside = new MyClass(UpdateLabel);
outside.MyMethod();
}
a bit unsure because the example actually leaves some bits unclear... but here is a try:
public class MyClass
{
public void MyMethod(Form1 F)
{
F.UpdateLabel("outside");
}
}
this works as long as MyClass is NOT running on a different thread - otherwise the call to UpdataLabel must be synchronized with the UI thread...
EDIT:
private void buttonOut_Click(object sender, EventArgs e)
{
MyClass Outside = new MyClass();
Outside.MyMethod(this);
}
Either go with Yahia's way (it has been updated and will work correctly) or try the following (probably overkill for what you're trying to do... whatever that is).
UPDATE:
Based on your comment in the question, you are also doing the work in MyClass on a different thread. Code change is below.
public partial class Form1 : Form
{
// keep a reference to a MyClass object for your Form's lifetime
private MyClass _myClass;
public Form1()
{
InitializeComponent();
// Intstantiate your MyClass object so you can use it.
_myClass = new MyClass();
// Register to the MyClass event called UpdateLabel.
// Anytime MyClass raises the event, your form will respond
// by running the UpdateLabelFromMyClass method.
_myClass.UpdateLabel += UpdateLabelFromMyClass;
}
private void button1_Click(object sender, EventArgs e)
{
// Call MyMethod in your MyClass object. It will raise
// the UpdateLabel event.
// update, you are calling this on a background thread?
_myClass.MyMethod();
}
void UpdateLabelFromMyClass(string message)
{
// Update your label with whatever message is passed in
// from the MyClass.UpdateLabel event.
// UPDATE: If called from a background thread you'll need this:
this.BeginInvoke( (Action) (()=>
{
label1.Text = message;
}));
}
}
public class MyClass
{
// An event that can be raised, allowing other classes to
// subscribe to it and do what they like with the message.
public event Action<string> UpdateLabel;
public void MyMethod()
{
// Raise the UpdateLabel event, passing "Outside" as
// the message.
UpdateLabel("Outside");
}
}
After wasting a ton of time on what should be a simple task and trying every answer on stack overflow, I said, if C# wants to make it stupid hard to change the text of a simple label, I am going to come up with a stupid fix.
Here is what you do:
In Form1 or whatever form has the label you want add:
public void setStatus()
{
lblStatus.Text = status;
}
public static string status;
Now, add a timer to Form1 and have it run "setStatus();" on every tick
Now, in any class, just write:
Form1.status = "Change label to this text";
you need to make both the method MyMethod and the label in question static. But if you do then you cannot access MyMethod through a new instance of the form instead you have to access it directly like Form1.MyMethod(). But if you do make the label the static visual studio will make it non-static one you access the label from the designer so you will have to keep making it static from form1.designer.cs. Also if you do make the label static change every line that refers to any of its properties so if it says this.label1.Text change it to label1.Text. This should give you the desired effect
I have a simple forms program that I have been fighting with for a while now. I simply want to be able to call a method from a different class file (when a certain step is triggered in the code in that class file) in order to insert a string in the listBox.
Here is my main method, pretty standard:
class Program
{
[STAThread]
static void Main(string[] args)
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new MainForm());
}
}
Here is the function which resides in my MainForm.cs file, which I can call just fine from that class file (via 'TextToBox(myString);'):
public partial class MainForm : Form
{
...
// Function to output results to main Listbox window
public void TextToBox(string aString)
{
// Place messages in Main Display list box window
this.listBox1.Items.Insert(0, aString);
}
...
}
But my problem is when I am in another class and I want to call 'TextToBox(myString);'. If I create another object reference of the MainForm, the code compiles fine but nothing will show up in the listBox. How do I do this? I cannot simply make TextToBox() static. I know I must create the object reference but I can't figure out how to reference the ORIGINAL MainForm, the one that was created in the Main method. Thanks in advance...
This will work, but only when you have one instans of MainForm.
public class MainForm : Form
{
public MainForm()
{
Instance = this;
}
public static MainForm Instance { get; private set; }
// Function to output results to main Listbox window
public void TextToBox(string aString)
{
// Place messages in Main Display list box window
this.listBox1.Items.Insert(0, aString);
}
}
public class Other
{
public void AddTextToListBox()
{
MainForm.Instance.TextToBox("Test");
}
}
...Edit...
Alternative:
class Program
{
public static MainForm MainFormInstance;
[STAThread]
static void Main(string[] args)
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
MainFormInstance = new MainForm();
Application.Run(MainFormInstance);
}
}
public class Other
{
public void AddTextToListBox()
{
Program.MainFormInstance.TextToBox("Test");
}
}
I would just pass a delegate to the other class.
/* this runs (previous code was not guaranteed to run) */
class OtherClass
{
public delegate void TextToBox(string s);
TextToBox textToBox;
int next = 0;
public OtherClass(TextToBox ttb)
{
textToBox = ttb;
}
public void SendSomeText()
{
textToBox(next.ToString());
next++;
}
}
I'm assuming you'll be instantiating OtherClass from MainForm. Is this how you're calling "OtherClass"?
public partial class MainForm : Form
{
OtherClass otherClass;
public MainForm()
{
/* just two controls -- listBox1 and button1 */
InitializeComponent();
otherClass = new OtherClass(this.TextToBox);
}
public void TextToBox(string aString)
{
listBox1.Items.Add(aString);
}
private void button1_Click(object sender, EventArgs e)
{
otherClass.SendSomeText();
}
}
On a button click the next numeric value is added at the beginning of the ListBox. You'll have to post some of your code if you need further help.
alternatively you could use a singleton pattern, or static methods and make sure you include the class in a 'using' statement at the top of your program