Problem with UIScrollView Content Offset

问题:

Im developing an iPad app in which I have a scrollview, the size of which i determine dynamically depending on the number of objects i display in it. Now, though i have not set any content offset I find that the scroll view has been offset by some amount whenever the view loads. When I check the value of the offset, it shows 0. I dont understand why without having a contentOffset value, the scrollview behaves that way. Any reasons for this?

I suspect this has something to do with iOS 4.2 as i dont remember this problem occurring when i was testing the app on iOS 3.2.

Update: The amount its getting offset seems to vary based on the contentSize of the scrollView. If the contentSize of the scrollView matches that of its frame height (its a vertical scrollview), then there is no offset. As the contentSize increases above the value of the height of the scrollView frame, the offset also increases proportionally. However, scrollView.contentOffset.y still = 0.0

回答1:

if u use interface builder -

• add scrollview to the view
• create another view and add elements that u need to add to scroll view

then add this second view to scrollview

write this code in Viewdidload scrollview.contentsize.y = lastelement.frame.origin.y + lastelement.frame.size.height + 10

this will adjust the scrollview to content size. it displays the first element and can scroll from top to bottom.

回答2:

The UIScrollView definitively does not behave the same way on iPad with iOS 4.2.1 than in iOS 3. I don't yet know if it's a bug or if I missed something in the documentation about an evolution.

My scrollview was created in a xib and I was reusing it to display different object of the same class. In my code, I only modified the contentSize of this scrollview.

The offset remained at 0 when looking with NSLog, but was varying on screen.

To fix my problem, I ended up creating programmatically a new scrollview each time I was displaying a new object. Might not be possible in your case, but for me, problem solved worked around.

回答3:

I faced same problem. Solved by keeping code for setting scrollview in viewWillAppear:animated

-(void) viewWillAppear:(BOOL)animated
{
    scrollView.frame = self.view.frame;
    scrollView.contentSize = self.view.frame.size;
} 

回答4:

If you use Auto Layout and want to set the offset for the scroll view contents, this is what worked for me:

- (void)viewDidLayoutSubviews {
     [super viewDidLayoutSubviews];
     self.myScrollView.contentOffset = CGPointMake(500, 0);
}

回答5:

Assign the sum of frame.origin value and frame.height value of last element to scrollView.contentOffset.y

回答6:

Also in Swift

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    scrollView.contentOffset = CGPointZero
}