Question

I am dealing with and odd bug, I have created a custom segmented control that comprises of uibuttons (the controller itself is a subclass of UIView. I change the button’s images for the selected and normal control state to indicate selection.

In my parent view in IB I have set the identity of the view to my custom class. The issue is I have a tableView, when I scroll it and the scroll animation the button inside my custom view does not change its image immediately, instead it waits for the table to finish scrolling and then it updates. Any ideas?

Answer 1

You’re not giving a lot of detail, but it sounds as if you’re trying to do too much work within the current run loop. If so then the answer will be relevant:

iOS waits until your code has finished executing before it does any display updating. So any updates are, in effect, queued until your current chunk of code is completed. To get around this, the most common trick is to allow the current run loop to end and the pick up execution again after a very short delay.

So, in your case, call the code to update your custom segment control. And then, instead of calling the code to update your table, park that code in another method and call that method using [self performSelector: @selector(delayedUpdate) withObject: nil afterDelay:0.1];

To illustrate how you might change code:

BEFORE

 [self updateSegmentController];
 [self updateTableScrollPosition];
 return;

AFTER

 [self updateSegmentController];
 [self performSelector: @selector(updateTableScrollPosition) withObject: nil afterDelay: 0.1];
 return;

Often a delay of 0.0 works just fine; it still achieves the effect of letting the current run loop complete and the display update before calling the nominated method. Sometimes adding an extra delay improves your animation appearance.