Programmatically resize NSView

I have a main view that is supposed to display several subviews. Those subviews are directly above and below one another (in the z axis) and will drop down (in the y axis) and move up using this code:

if (!CGRectIsNull(rectIntersection)) {
    CGRect newFrame = CGRectOffset (rectIntersection, 0, -2);
    [backgroundView setFrame:newFrame];
} else{
    [viewsUpdater invalidate];
    viewsUpdater = nil;
}

rectIntersection is used to tell when the view has entirely moved down and is no longer behind the front one (when they no longer overlap rectIntersection is null), it moves down by 2 pixels at a time because this is all 开发者_运维问答inside a repeating timer. I want my main view, the one that contains these two other views, to resize downward so that it expands just as the view in the background is being lowered. This is the code I'm trying for that:

CGRect mainViewFrame = [mainView frame];
if (!CGRectContainsRect(mainViewFrame, backgroundFrame)) {
    CGRect newMainViewFrame = CGRectMake(0,
                                         0,
                                         mainViewFrame.size.width,
                                         (mainViewFrame.size.height + 2));
    [mainView setFrame:newMainViewFrame];
}

The idea is to check if the mainView contains this background view. When the backgroundView is lowered, the main view no longer contains it, and it (should) expand downward by 2 pixels. This would happen until the background view stopped moving and the mainView finally contains backgroundView.

The problem is that the mainView is not resizing at all. the background view is being lowered, and I can see it until it disappears off the bottom of the mainView. mainView should have resized but it does not change in any direction. I tried using setFrame and setBounds (with and without setNeedsDisplay) but nothing worked.

I'm really just looking for a way to programmatically change the size of the main view.

I think I understood, what the problem is. I read carefuly the code.

if (!CGRectIsNull(rectIntersection)) {
    // here you set the wrong frame
    //CGRect newFrame = CGRectOffset (rectIntersection, 0, -2);
    CGRect newFrame = CGRectOffset (backgroundView.frame, 0, -2);
    [backgroundView setFrame:newFrame];
} else{
    [viewsUpdater invalidate];
    viewsUpdater = nil;
}

rectIntersection is actually the intersection of the two views, that overlap, and as the backgroundView is moved downward, that rect's height decreases.
That way the mainView gets resized only one time.

To add on this, here is a simple solution using block syntax, to animate your views, this code would typically take place in your custom view controller.

// eventually a control action method, pass nil for direct call
-(void)performBackgroundViewAnimation:(id)sender {
    // first, double the mainView's frame height
    CGFrame newFrame = CGRectMake(mainView.frame.origin.x,
                                  mainView.frame.origin.y,
                                  mainView.frame.size.width,
                                  mainView.frame.size.height*2);
    // then get the backgroundView's destination rect
    CGFrame newBVFrame = CGRectOffset(backgroundView.frame,
                                      0,
                                      -(backgroundView.frame.size.height));
    // run the animation
    [UIView animateWithDuration:1.0
                     animations:^{
                                     mainView.frame = newFrame;
                                     backgroundView.frame = newBVFrame;
                                 }
    ];
}