Resizing a UIView - expanding the top

Question

I have a UIView inside of a UIScrollView that I want to resize.

I can increase the height easily by :

CGRect frame = self.drawinView.frame;
frame.size.height += 100;
self.drawinView.frame = frame;
self.drawinScrollView.contentSize = CGSizeMake(frame.size.width, frame.size.height);

And all is good.

The above code will create a new area of the view at the bottom of the view that I can fill out.

Now when I resize the view, I only want to be repainting the new portion of the view that has just been created. I dont want to have to repaint the whole view.

However! I have run into difficulty when I need to expand the top of the view.

Doing :

CGRect frame = self.drawinView.frame;
frame.origin.y -= 100;
self.drawinView.frame = frame;
self.drawinScrollView.contentSize = CGSizeMake(500, 600);

does not work.

How can I do this without having to repaint the entire view?

Answer 1

In the above code you are only changing the origin of the view. Not it's size.

Answer 2

You can set the content size to any large number you want, but you can never scroll further left or up than the top-left corner at 0,0. If you have a view with y at -100, it will not let you scroll to the 100px above 0.

Instead, you need to leave it where it is and instead set the contentOffset to +100 vertically.

If, for example, you want to resize the view by 100px up, you would do this:

CGRect frame = self.drawinView.frame;
frame.size.height += 100;
self.drawinView.frame = frame;
self.drawinScrollView.contentSize = CGSizeMake(frame.size.width, frame.size.height);
self.drawinScrollView.contentOffset = CGPointMake(0,100);

You would some how have to manually tell the drawinView that you want to lock the contents to the bottom of the view instead of the top.