C# / GTK Question

[PaulM1985]

Hi

I have started to mess around with C# and GTK in Monodevelop. I come from a Java background and I am used to adding action listeners to buttons and then implementing inner classes to deal with button clicks.

How do I add a similar thing to a button using C# and GTK? I have found gtk_button_clicked(GTKButton *button) in the GTK documentation, but I am not sure if I am supposed to implement this method or if it already exists, and if I do have to implement it, where do I do it?

I am very new to C# so sorry if I have missed something really obvious.

Paul

[cabalas]

To handle an event in C# you need to add a new event handler to the event. An event handler takes a function as a parameter which is what is called when the even is triggered. The code for it looks like this.



button1.Clicked += new EventHandler(onButtonClicked);


Generally you will of declared the function onButtonClicked somewhere else in your class.

[PaulM1985]

Hi

I tried:



using System;
using Gtk;

public partial class MainWindow: Gtk.Window
{
public MainWindow (): base (Gtk.WindowType.Toplevel)
{
Build ();
button1.Clicked += new EventHandler(ButtonClick());
}

protected void OnDeleteEvent (object sender, DeleteEventArgs a)
{
Application.Quit ();
a.RetVal = true;
}

public void ButtonClick()
{
Console.Write("Button Clicked \n");
}
}


But I get the error: Method name expected, on the button1.Clicked line.

The actual adding of the button has been done by the GUI Builder.

Paul

[sakabato]

There should be no paranthesis there.


button1.Clicked += new EventHandler(ButtonClick);


Notice there is no paranthesis after ButtonClick


Also the following is correct as well:

button1.Clicked += new ButtonClick;




Finally your event handler should be as below :

public void ButtonClick(object sender, EventArgs e)
{
Console.Write("Button Clicked \n");
}



I also strongly recommend you should read about the basics of events and delegates.




button1.Clicked += ButtonClick;

Also your ButtonClick methods' signature isnot EventHandler

It should be

[jespdj]

Is that the complete application? button1 in the example is the name of a variable, but you did you declare a variable named 'button1' anywhere in your source code - so the compiler will complain that it doesn't know what you mean with 'button1'.

[PaulM1985]

Thanks sakabato. That got it working. I will look into the things you have mentioned. I have found a tutorial on GTK that I am going to go through to help.

Thanks again.

Paul

[SKLP]

Also you can use anonymous delegate (i.e. closures) to handle the events, like so:


[...]
int a = 0;
button1.Clicked += delegate {
a++;
button1.Label = "Clicked " + a.ToString() + "times";
};
[...]

(havent checked if the property is really called "Label" but you get the picture...)

also if you need to handle the parameters a good way may be to use lambdas as then the parameter types can be inferred, such as:


[...]
button1.Clicked += (sender, eventargs) => {
[...]
};
[...]


Also, you can use the GTK#-specific docs rather than the ones meant for plain GTK.
http://www.go-mono.com/docs/

[directhex]

Is that the complete application? button1 in the example is the name of a variable, but you did you declare a variable named 'button1' anywhere in your source code - so the compiler will complain that it doesn't know what you mean with 'button1'.

MonoDevelop stores declarations of variables designed using the GUI designer in a partial class, i.e. they're all automatically linked & available inside your code