Does calling -setNeedsDisplay from a background task call for problems?

Question

I have a background task that updates a view. This task calls -setNeedsDisplay to display the view.

It works:

- (void) drawChangesTask;
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    if (pixels) {
        drawChanges((UInt32 *) origPixels, (UInt32 *) pixels, CGBitmapContextGetBytesPerRow(ctx)/4, CGBitmapContextGetHeight(ctx), count--);

        if (count < 0) {
            count = 150;
        }
        else
            [self performSelectorInBackground:@selector(drawChangesTask) withObject:nil ];

        [self performSelectorOnMainThread:@selector(setNeedsDisplay) withObject:nil waitUntilDone:NO ];

    }
    [pool release];
}

This does not work:

- (void) drawChangesTask;
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    if (pixels) {
        drawChanges((UInt32 *) origPixels, (UInt32 *) pixels, CGBitmapContextGetBytesPerRow(ctx)/4, CGBitmapContextGetHeight(ctx), count--);

        if (count < 0) {
            count = 150;
        }
        else
            [self performSelectorInBackground:@selector(drawChangesTask) withObject:nil ];

        [self setNeedsDisplay];

    }
    [pool release];
}

Does anyone know why? When I say that this does not work, I mean that it runs dozens of iterations, sometimes I see that parts of my image are shifted up or down or completely empty, and then the deagger gives me a " EXC_BAD_ACCESS" somewhere in CoreGraphics.

In addition, if I do not process the auto-advertisement myself, then I get a leak of error messages. I don’t understand why this is so. My drawChanges () does not create any new objects. Here's the error:

2009-08-17 11:41:42.358 BlurApp[23974:1b30f] *** _NSAutoreleaseNoPool(): Object 0xd78270 of class NSThread autoreleased with no pool in place - just leaking

Answer 1

UIKit - , UIKit .

, :

[self performSelectorInBackground:@selector(drawChangesTask) withObject:nil];

. ? runloop , :

[self performSelector:@selector(drawChangesTask) withObject:nil afterDelay:0.0];

, , , , runloop .

Answer 2

, UIKit , - nothign , , , performSelectorOnMainThread .