Question

I’m new to objective-c so bear with me. This seems pretty simple but I must be doing something wrong. In IB I created an object, called it AppController and then added an action titled makeView and two IBOutlets, btnMakeView and mainWin, then connected everything properly and wrote the class file from that.

In AppController.h I have this code:

#import <Cocoa/Cocoa.h>
@interface AppController : NSObject {
    IBOutlet NSWindow * mainWin;
    IBOutlet id btnMakeView;
}
- (IBAction)makeView:(id)sender;
@end

in AppController.m this code:

#import "AppController.h"
#import "ViewController.h"
@implementation AppController
- (IBAction)makeView:(id)sender {

    //declare a new instance of viewcontroller, which inherits fromNSView, were going to allocate it with 
    //a frame and set the bounds of that frame using NSMakeRect and the floats we plug in.
    ViewController* testbox = [[ViewController alloc]initWithFrame:NSMakeRect(10.0, 10.0, 100.0, 20.0)];

    //this tells the window to add our subview testbox to it's contentview
    [[mainWin contentView]addSubview:testbox];
}
-(BOOL)isFlipped {
    return YES;
}
@end

in ViewController.h I have this code:

#import <Cocoa/Cocoa.h>
@interface ViewController : NSView {
}
@end

and finally in ViewController.m I have this code:

#import "ViewController.h"

@implementation ViewController    
- (id)initWithFrame:(NSRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code here.
    }
    return self;
}

- (void)drawRect:(NSRect)rect {
    // Drawing code here.

    //sets the background color of the view object
    [[NSColor redColor]set];

    //fills the bounds of the view object with the background color
    NSRectFill([self bounds]);
}

@end

It compiles fine, there are no errors but do not get an object, which I am assuming will be a rectangle, starting at x,y 10/10 and being 100×20. What am I doing wrong?

Answer 1

Does mainWin refer to a valid window? Other than that, your code works, though it could use some improvement. For example,

• ViewController is a view, not a controller, so it shouldn’t be named a controller.
• You’ve got a memory leak. You never release the ViewController you create. The memory management rules are very simple; read up on them.

Try the following changes. First, rename ViewController to RedView (or SolidColorView or somesuch). You can do this very simply by refactoring: right-click the class name in the @interface or @implementation declaration and choose “Refactor…”.

In RedView.m:

- (id)initWithFrame:(NSRect)frame {
    // the idiom is to call super's init method and test self all in the
    // same line. Note the extra parentheses around the expression. This is a 
    // hint that we really want the assignment and not an equality comparison.
    if ((self = [super initWithFrame:frame])) {
        // Initialization code here.
    }
    return self;
}

In AppController.m:

- (IBAction)makeView:(id)sender {
    //declare a new instance of viewcontroller, which inherits fromNSView, were going to allocate it with 
    //a frame and set the bounds of that frame using NSMakeRect and the floats we plug in.
    RedView* testbox = [[RedView alloc] initWithFrame:NSMakeRect(10.0, 10.0, 100.0, 20.0)];

    //this tells the window to add our subview testbox to it's contentview
    // You don't need to keep a reference to the main window. The application already
    // does this. You might forget to hook up mainWin, but the following won't fail
    // as long as the app has a main window.
    [[[[NSApplication sharedApplication] mainWindow] contentView] addSubview:testbox];
    // We're done with testbox, so release it.
    [testbox release];
}