GTK, C# question

[DaMasta]

Teaching myself some GTK and C# using monodevelop. I created a button and would like to change a label's text when clicked. Here's what I have.


using System;
using Gtk;

class buMain {

static void Main()
{
Application.Init();
Window mainWindow = new Window("Easy Backup");
mainWindow.DeleteEvent += new DeleteEventHandler (delete_backuputil);
mainWindow.SetDefaultSize (200, 150);
VBox mbBox = new VBox(false,2);
//Creates a menubar
MenuBar mb = new MenuBar();
//Stars the file portion of the menubar
Menu file_menu = new Menu();
//Creation of the open option and then appends the open option to the file portion
MenuItem open_item = new MenuItem("Open...");
file_menu.Append(open_item);
//Creation of the exit option and then appends the exit option to the file portion
MenuItem exit_item = new MenuItem("Exit");
file_menu.Append(exit_item);
exit_item.Activated += new EventHandler (exit_backuputil);
MenuItem file_item = new MenuItem("File");
file_item.Submenu = file_menu;

//Stars the edit portion of the menubar
Menu edit_menu = new Menu();
//Creation of the policy option and then appends the policy option to the edit portion
MenuItem policy_item = new MenuItem("Policy...");
edit_menu.Append(policy_item);
MenuItem edit_item = new MenuItem("Edit");
edit_item.Submenu = edit_menu;

mb.Append(file_item);
mb.Append(edit_item);
mbBox.PackStart(mb, false, false, 0);
Label testLabel = new Label("no");
mbBox.PackStart(testLabel, false, false, 0);
Button testButton1 = new Button("testing1");
testButton1.Clicked += new EventHandler(change_label);
mbBox.PackStart(testButton1, false, false, 0);
Button testButton2 = new Button("testing2");
mbBox.PackStart(testButton2, true, true, 0);
mainWindow.Add(mbBox);
mainWindow.ShowAll();
Application.Run();
}
static void change_label (object obj, EventArgs args)
{
testLabel.Text = "Yes!";
}
static void delete_backuputil (object o, DeleteEventArgs args)
{
Application.Quit ();
}
static void exit_backuputil (object o, EventArgs args)
{
Application.Quit ();
}
}

And here is the error:
backuputil.cs(53,11): error CS0246: The type or namespace name `testLabel' could not be found. Are you missing a using directive or an assembly reference?
backuputil.cs(53,11): error CS0103: The name `testLabel' does not exist in the context of `buMain'
Compilation failed: 2 error(s), 0 warnings

[fct]

Your problem is that "testLabel" is declared in the Main() function. But that means it's a local variable, that can't be seen from functions other than Main() (as is the case with "change_Label").

You have two different solutions:

- The best one would be to declare testLabel as a property of class buMain (that is, for example, before the declaration of the Main() method). That way it would be available to any function inside buMain.

- Use GTK# functions to check for the label by travelling through all the tree structure that defines the window and its contents (unnecessary here, and worksome).

[dogen]

Yes, as fct says, the function change_label has no idea what testLabel is because it doesn't exist within its scope when change_label attempts to reference it.

It only exists within Main, which doesn't make it global to the class and doesn't make it visible to change_label.

[DaMasta]

Ok, so how would I go about doing this. I read there is no global variables in C#. I appreciate both of your help.

[fct]

using System;
using Gtk;

class buMain {
Label testLabel;

static void Main()
{
Application.Init();
Window mainWindow = new Window("Easy Backup");
mainWindow.DeleteEvent += new DeleteEventHandler (delete_backuputil);
mainWindow.SetDefaultSize (200, 150);
VBox mbBox = new VBox(false,2);
//Creates a menubar
MenuBar mb = new MenuBar();
//Stars the file portion of the menubar
Menu file_menu = new Menu();
//Creation of the open option and then appends the open option to the file portion
MenuItem open_item = new MenuItem("Open...");
file_menu.Append(open_item);
//Creation of the exit option and then appends the exit option to the file portion
MenuItem exit_item = new MenuItem("Exit");
file_menu.Append(exit_item);
exit_item.Activated += new EventHandler (exit_backuputil);
MenuItem file_item = new MenuItem("File");
file_item.Submenu = file_menu;

//Stars the edit portion of the menubar
Menu edit_menu = new Menu();
//Creation of the policy option and then appends the policy option to the edit portion
MenuItem policy_item = new MenuItem("Policy...");
edit_menu.Append(policy_item);
MenuItem edit_item = new MenuItem("Edit");
edit_item.Submenu = edit_menu;

mb.Append(file_item);
mb.Append(edit_item);
mbBox.PackStart(mb, false, false, 0);
// Don't declare this here, do it in the class scope
// Label testLabel = new Label("no");
testLabel = new Label("no");
mbBox.PackStart(testLabel, false, false, 0);
Button testButton1 = new Button("testing1");
testButton1.Clicked += new EventHandler(change_label);
mbBox.PackStart(testButton1, false, false, 0);
Button testButton2 = new Button("testing2");
mbBox.PackStart(testButton2, true, true, 0);
mainWindow.Add(mbBox);
mainWindow.ShowAll();
Application.Run();
}
static void change_label (object obj, EventArgs args)
{
testLabel.Text = "Yes!";
}
static void delete_backuputil (object o, DeleteEventArgs args)
{
Application.Quit ();
}
static void exit_backuputil (object o, EventArgs args)
{
Application.Quit ();
}
}

[DaMasta]

Yeah, I tried it that way and it spits out:

burerun.cs(42,3): error CS0120: `testLabel': An object reference is required for the nonstatic field, method or property
burerun.cs(43,19): error CS0120: `testLabel': An object reference is required for the nonstatic field, method or property
burerun.cs(55,12): error CS0120: `testLabel': An object reference is required for the nonstatic field, method or property
Compilation failed: 3 error(s), 0 warnings

[fct]

try:

.......
class buMain {
static Label testLabel;
.......

But the thing is that you should watch some more examples. Usually you don't init widget properties in Main(), but in the class constructor.

[DaMasta]

try:

.......
class buMain {
static Label testLabel;
.......

But the thing is that you should watch some more examples. Usually you don't init widget properties in Main(), but in the class constructor.
Yep, that worked. Thanks fct. I'm learning as I go. I really appreciate your help.