为什么UIScrollView无法弹跳？

Question

I do this:

    scrollView = [[UIScrollView alloc] initWithFrame:self.bounds];
    [self addSubview:scrollView];

    NSInteger x = scrollView.bounds.origin.x + Padding, y = scrollView.bounds.origin.y + Padding;

    backButton = [[AButtonControl alloc] initWithCaption:@"Back" style:AButtonViewStyleGreen];
    backButton.frame = CGRectMake(x, y, backButton.frame.size.width, backButton.frame.size.height);
    y += backButton.frame.size.height + Spacing;
    [scrollView addSubview:backButton];

    ownerNameTextField = [[AFormTextField alloc] initWithFrame:CGRectMake(x, y, 200, 60) label:@"Guest name"];
    y += ownerNameTextField.frame.size.height + Spacing;
    [scrollView addSubview:ownerNameTextField];

    guestListSelectField = [[AFormSelectField alloc] initWithFrame:CGRectMake(x, y, 200, 60) label:@"Guest list"];
    y += guestListSelectField.frame.size.height + Spacing;
    [scrollView addSubview:guestListSelectField];

    referenceUserSelectField = [[AFormSelectField alloc] initWithFrame:CGRectMake(x, y, 200, 60) label:@"Reference user"];
    y += referenceUserSelectField.frame.size.height;

    [scrollView addSubview:referenceUserSelectField];

    scrollView.contentSize = CGSizeMake(self.bounds.size.width, y + Padding);

And it scrolls fine, but the view does not bounce like it is supposed(?) to.

Any ideas?

Answer 1

The underlying problem here is if you set the scrollview's frame/bounds in -layoutSubviews, it doesn't check if you're setting it to the frame/bounds that it already has, and this cancels the bounce. The solution is to do something like

CGFrame scrollFrame = [self calculateFrameForScrollView];
if (!CGRectEqualToRect(scrollFrame, self.myScrollView.frame)) 
    self.myScrollView.frame = scrollFrame;

Found at: UIScrollView and its subclasses won't bounce if nested in custom UIView