Why a frame of a UIView is not updating in ViewDidLayoutSubviews?

问题

I am trying to update the frame of a UIView which contains buttons and labels inside. I am trying to update it in viewDidLayoutSubviews (and I also tried in viewDidLoad, viewWillAppear, viewDidAppear..). I want to change the y position (origin.y) of the view. The NSLogs says my original y position is 334, and after changing, it is 100. However, the position does not change in my view. I have already checked that the view is connected in the storyboard. What am I doing wrong?

-(void)viewDidLayoutSubviews
{
    [super viewDidLayoutSubviews];
    CGRect theFrame  = [self.bottomView frame];
    NSLog(@"Y position bottomview: %f", self.bottomView.frame.origin.y);

    if([[UIScreen mainScreen] bounds].size.height == 568) //iPhone 4inch
    {
       // NSLog(@"iphone5");
    }
    else{
       // NSLog(@"iphone4");
        theFrame .origin.y =  100;
    }

    self.bottomView.frame = theFrame;
    NSLog(@"Y position bottomview after changing it: %f", self.bottomView.frame.origin.y);
    [self.view layoutIfNeeded];
}

回答1:

I've had the same problem. Forcing the layouting for your view's superview helped me out:

-(void)viewDidLayoutSubviews
{
    [super viewDidLayoutSubviews];
    [self.bottomView.superview setNeedsLayout];
    [self.bottomView.superview layoutIfNeeded];

    // Now modify bottomView's frame here
}

In Swift:

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    bottomView.superview!.setNeedsLayout()
    bottomView.superview!.layoutIfNeeded()

    // Now modify bottomView's frame here
}

回答2:

The problem was related with Autolayout. However I couldn't turn it off since I am using autolayout in my project. I solved defining appropriate constraints in the view. Then there is no need to check if it is iPhone 4inch or 3.5inch and change the position of the frame since it automatically adapts to each size.

回答3:

Believe it or not the below code fixed it

override func viewDidLayoutSubviews() {
    DispatchQueue.main.async {
        // UI changes
    }
}

来源：https://stackoverflow.com/questions/22488728/why-a-frame-of-a-uiview-is-not-updating-in-viewdidlayoutsubviews