6 - Adding a Button in the Window

We are now going to add a button inside our window. But first, we need to prepare the ground with a very short introduction to the wonderful NSView class.

6.1 A Quick Introduction to Views

NSView is a class whose objects represent a rectangular area in a window. Each NSView has its own internal coordinate system; NSView provides a complete framework for managing the rectangle represented by the view, its coordinate system, and for drawing and getting user events inside the view’s rectangle.

Any object which can be displayed (and/or can accept user events) inside a window (such as a button, a text field, a scroll view, a slider, etc) is actually an instance of a subclass of NSView. The specific subclass (for example, NSButton) implements a specific way of drawing and managing user events inside the view’s rectangle. An unsubclassed NSView by default draws nothing and reacts to no user events, even if it contains all the machinery (ready for subclasses to use) to do both.

When you create a window, the library automatically creates an NSView covering the whole content area of the window. This view is called the window’s content view. You can replace the default content view (which is transparent and reacts to no user events) with an NSView of your choice (which can be an instance of a subclass of NSView, such as a NSButton or a NSScrollView), but you should not change the rectangle it represents, which must always cover the whole window.

If you want to have a view which covers only a part of a window, you need to add it as a subview of the content view. We will explore subviews in a forth-coming tutorial; in our first example, we will go for the simplest possible solution avoiding use of subviews: we will create a single NSButton, make a window to fit exactly our button, and then replace the default window’s content view with our button. In this way we’ll get a window containing exactly our button. In the next tutorial, we’ll learn how to enclose views one over the other in a subview tree, so that we can put more things in a single window.

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6.2 Creating a Button

Creating a button is quite easy:

NSButton *myButton;

myButton = AUTORELEASE ([NSButton new]);
[myButton setTitle: @"Print Hello!"];
[myButton sizeToFit];

setTitle: sets the title (string) to be displayed on the button; sizeToFit resizes the button so that it fits the title it is displaying.

Next, we need to set target and action of the button:

[myButton setTarget: self];
[myButton setAction: @selector (printHello:)];

(self will refer to our custom object)

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6.3 Putting the button in the window

We now need to modify our code to create the window so that it creates a window exactly of the right size to contain our button. First, we need to get the size of the button:

NSSize buttonSize;

buttonSize = [myButton frame].size;

frame is a method inherited by NSView which returns the rectangle enclosing the button (or, more generally, the rectangle enclosing/represented by an NSView). The origin of this rectangle is meaningless at this point; it is the size (which was set by sizeToFit) what we want.

Then, we choose for the window a content rect with the size of the button, and with an origin of our choice; (100, 100) in this example:

NSRect rect;

rect = NSMakeRect (100, 100, 
                   buttonSize.width, 
                   buttonSize.height);

At this point, we just create the window as before, but using this rectangle (full code below). The last thing to do is then replacing the default window content view with our button:

[myWindow setContentView: myButton];

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6.4 Source Code

We are ready to show the whole source code (the GNUmakefile is the usual one):

#include <Foundation/Foundation.h>
#include <AppKit/AppKit.h>

@interface MyDelegate : NSObject
{
  NSWindow *myWindow;
}
- (void) printHello: (id)sender;
- (void) createMenu;
- (void) createWindow;
- (void) applicationWillFinishLaunching: (NSNotification *)not;
- (void) applicationDidFinishLaunching: (NSNotification *)not;
@end

@implementation MyDelegate : NSObject 
- (void) dealloc
{
  RELEASE (myWindow);
}

- (void) printHello: (id)sender
{
  printf ("Hello!\n");
}

- (void) createMenu
{
  NSMenu *menu;

  menu = AUTORELEASE ([NSMenu new]);

  [menu addItemWithTitle: @"Quit"  
        action: @selector (terminate:)  
        keyEquivalent: @"q"];

  [NSApp setMainMenu: menu];
}

- (void) createWindow
{
  NSRect rect;
  unsigned int styleMask = NSTitledWindowMask 
                           | NSMiniaturizableWindowMask;
  NSButton *myButton;
  NSSize buttonSize;

  myButton = AUTORELEASE ([NSButton new]);
  [myButton setTitle: @"Print Hello!"];
  [myButton sizeToFit];
  [myButton setTarget: self];
  [myButton setAction: @selector (printHello:)];

  buttonSize = [myButton frame].size;
  rect = NSMakeRect (100, 100, 
                     buttonSize.width, 
                     buttonSize.height);

  myWindow = [NSWindow alloc];
  myWindow = [myWindow initWithContentRect: rect
                       styleMask: styleMask
                       backing: NSBackingStoreBuffered
                       defer: NO];
  [myWindow setTitle: @"This is a test window"];
  [myWindow setContentView: myButton];
}

- (void) applicationWillFinishLaunching: (NSNotification *)not
{
  [self createMenu];
  [self createWindow];
}

- (void) applicationDidFinishLaunching: (NSNotification *)not;
{
  [myWindow makeKeyAndOrderFront: nil];
}
@end

int main (int argc, const char **argv)
{ 
  [NSApplication sharedApplication];
  [NSApp setDelegate: [MyDelegate new]];

  return NSApplicationMain (argc, argv);
}

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