Event Loop Question

[coulls]

Hi all,

OK - I have a loop that needs to repeatedly call setBackgroundColor on a UIImageView using a series of different periods. If you were to imaging a morse code flasher, you'd be along the same lines with the dots and dashes being different lengths, along with a predefined "gap" in the middle. The problem is the loop doesn't give the view time to actually process the call - so I'm scratching my head over which way to do this.

Two ways I've come up with is pre-scheduling an NSTimer to fire at all the future points, or to use an NSThread to fire over and over and then switch the view...

Both ways appear in my head to be a bit complicated - but bare in mind the 20 years of VB "training" I had before starting with Objective-C a few years back.

Cheers,

Jase

[coulls]

Update: So, I tried putting the task code into a dispatch queue. It ran identical to how it did in the loop, in that the screen still had no chance to catch up and process the setBackgroundColor messages...

*scratches head*

Will go back to the drawing board.

Cheers,

Coulls

[Duncan C]

Originally Posted by coulls

Update: So, I tried putting the task code into a dispatch queue. It ran identical to how it did in the loop, in that the screen still had no chance to catch up and process the setBackgroundColor messages...

*scratches head*

Will go back to the drawing board.

Cheers,

Coulls

You're not supposed to make UI changes except from the main thread. If you want to control everything from a worker thread, use performSelectorOnMainThread from the worker thread to get the main thread to update the UI.

Another way to do this without using threads is to use the method performSelector:withObject:afterDelay.

You could fire off the same method with different delays, and have the method change the color as needed.

The code below assumes you have an outlet theView to the view who's background color you want to change, an integer instance variable colorIndex, and another NSArray instance variable colorsArray that contains an array of UIColor objects:

-(void) nextColor
{
  theView.backgroundColor = [colorsArray objectAtIndex: colorIndex];
  colorIndex++;
}

-(void) beginFlashing;
{
  colorIndex = 0;
  int index;
  int count = 10;
  //Create a C array of different delays for the different steps.
  //We could also use an NSArray of NSNumbers. I was just lazy.
  float[] delays = {0.2, 0.3, 0.5, 0.9, 1.0, 1.5, 1.9, 2.2, 2.7, 3.0}

  for (index = 0; index < count; index++)
  {
    [self performSelector: @selector(nextColor) 
      withObject: nil 
      afterDelay: delays[index]
    ];
  }

[coulls]

Originally Posted by Duncan C

You're not supposed to make UI changes except from the main thread. If you want to control everything from a worker thread, use performSelectorOnMainThread from the worker thread to get the main thread to update the UI.[/code]

Doh! Now I feel like a twit... Will try again tonight and let you know how it pans out...

Thanks!

Jase