Dynamically changing UIView Frame

Question

I have a scenario like this: View B frame depends of View A frame. I am playing around with viewA frame. But the view b frame doesn't get changed because frame is not a object. So what the workaround, if I need to change the View B frame wrt to View A Frame ie view B frame gets changed when I change ViewA Frame

Answer 1

One Solution is add KVO for View A as it will notify when frame changed and according to change in frame of view A , change frame of view B

[A addObserver:self forKeyPath:@"frame" options:NSKeyValueObservingOptionOld context:NULL];  //added KVO for View A

Method would be:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
 if([keyPath isEqualToString:@"frame"]) {
  //change frame of View B according to View A
 }
}

EDIT : Remove observer when not needed

[A removeObserver:self forKeyPath:@"frame"];

Answer 2

In >iOS6, you can try to setup some autolayout constraints, or try this way:

[self addObserver:self forKeyPath:@"viewA.frame" options:NSKeyValueObservingOptionOld context:NULL];

Be sure to removeObserver on dealloc. Then, you'll find out when viewA frame changes, and you can implement any set of actions and any functional relationship between viewA and viewB frames...

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if([keyPath isEqualToString:@"viewA.frame"]) {
        // change viewB's frame according to viewA's frame
        viewB.frame = CGRectOffset(viewA.frame, 20.0, 20.0);
    }
}

Answer 3

Set the View B frame with respect to View A . Write a method -(void)ResizeFrame and put all frame settings in it and call this function when ever you need to change frame. ie ViewB.frame=[ViewA.frame.origin.x,ViewA.frame.origin.y,ViewA.frame.size.width/2,ViewA.frame.size.height/2]; Here i have given division you can change it accordingly.