Databases
StackOverflow2013
Postsdbo
POSwapping UIImageView Images in a loop
Body
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POSwapping UIImageView Images in a loop
    text
    copied!<p>I have a NSArray of UIImageViews that I want to loop over and quickly swap out an "on" and "off" state. I wrote the code to do so in a for loop instead a method that was called when the user tapped a UIButton ( the button's action ). </p> <p>Here's that loop:</p> <pre><code>for(int i = 0; i &lt; [Images count]; i++) { if( i &gt; 0 ){ [self toggleImageViewOff:[Images objectAtIndex:i - 1]]; } [self toggleImageViewOn:[Images objectAtIndex:i]]; [NSThread sleepForTimeInterval:0.5f]; } </code></pre> <p>The UI did not update as I expected as I only ever saw the last UIImageView in the "on" state. I figured that the drawing update of the views must occur in the main thread this code was also executing in. So I learned about performSelectorInBackground:withObject: . Performing the toggleImageViewOn/Off methods using this made the loop work. The problem is if I make the sleep interval too short I can have an "on" update after an "off" with Threads operating out of order. </p> <p>So I had the bright idea of moving the whole loop with the sleep into its own method and calling that from the action method using performSelectorInBackground:withObject: . I tried that and I'm back to not getting an updated view until the loop is over. </p> <p>That's a long winded way to get to my question:</p> <p>What's the best way to animate this to guarantee the on/off code fires in the right order and still get view updates, even at high speeds? ( i.e. looping very quickly ) </p> <p>I tried to think about how I'd do it with CoreAnimation, but I can't seem to get my head around how to do it there. </p> <p>For bonus, here are the toggle methods:</p> <pre><code>- (void)toggleImageViewOn:(UIImageView *)theImageView { [theImageView setImage:[UIImage imageNamed:@"on.png"]]; } - (void)toggleImageViewOff:(UIImageView *)theImageView { [theImageView setImage:[UIImage imageNamed:@"off.png"]]; } </code></pre>
 

Querying!

 
Guidance
An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload