iOS pull-down refresh UIScrollVie exception flashing problem

It is said that it was after IOS8, but I encountered a problem in iOS10. The pull-down refresh I used before may shake. When the slider is quickly released, the scrollView will return to the state of "refreshing..." process.

Reasons for jitter:

ScrollViewDidEndDragging => setContentInset:

In order to ensure that the pull-down refresh control can be displayed in the "Loading" state, we have made changes to the contentInset and added the top of the inset. So why does this step cause the scrollView to shake?

I made a breakpoint in scrollViewDidScroll: to see what happened after setContentInset:. I set = 64; and found that the contentOffset of scrollView has changed like this:

(0, -64) => (0, -133) => (0, -64)

From the above data, we can see that contentOffset is first moved down for a period of time during this process, and then returns to normal. Guess the cause of the problem:

After the pull-down is released, the bounce effect of scrollView itself conflicts with the current setting inset

Preliminary attempt: async

After knowing the cause of the problem, my first idea was to avoid this conflict, so I called the setContentInset: method asynchronously:

dispatch_async(dispatch_get_main_queue(), ^{
      [UIView animateWithDuration:kAnimationDuration animations:^{
         = inset;
      } completion:^(BOOL finished) {
      }];
    });

I tried it and there was no problem. But later someone encountered such a problem. After verification, it was indeed not completely fixed.

Secondary modification: Forced contentOffset

Since it is caused by the change of contentOffset, I will just set contentOffset again. So a second attempt:

dispatch_async(dispatch_get_main_queue(), ^{
      [UIView animateWithDuration:kAnimationDuration animations:^{
         = inset;
         = CGPointMake(0, -);
      } completion:^(BOOL finished) {
      }];
    });

The test results found that it was useless and the problem still existed. I spent a lot of time at this step and tried my best to solve the problem but couldn't solve the problem. Until I changed the setContentOffset: method to setContentOffset:animated: . The problem was solved, and it can be seen that the implementation of these two methods in the system is different.

dispatch_async(dispatch_get_main_queue(), ^{
      [UIView animateWithDuration:kAnimationDuration animations:^{
         = inset;
        [ setContentOffset:CGPointMake(0, -) animated:NO];
      } completion:^(BOOL finished) {
      }];
    });

The above is the iOS drop-down refresh problem introduced by the editor to you. UIScrollVie is abnormally flashing. I hope it will be helpful to everyone. If you have any questions, please leave me a message and the editor will reply to everyone in time. Thank you very much for your support for my website!