Crash with CALayer, memory problem

My thanks to hotpaw2 for the solution to my incremental drawing problem. Alas, I discovered an issue with the solution as I implemented it. It reveals itself as a memory-induced crash when I press the botton at the bottom of the iphone to suspend the app and then restart it. (I can run the app indefinitely as long as I don't do this). The crash occurs at the indicated line below, which occurs in FooBar, a subclass of UIView:

- (void)drawRec开发者_运维百科t:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();

// @@CRASH here: Program received signal EXC_BAD_ACCESS 
[backingLayer renderInContext:ctx];     // Render the backing layer into current context
[self randomRectangle: ctx];

}

In the interface of FooBar I have declared backing layer as instance variable:

@private

NSTimer* timer;
CALayer *backingLayer;

In the implementation of FooBar, backingLayer occurs just once more, in initWithFrame, in the following paragraph:

    backingLayer = self.layer; 
    // [backingLayer retain];
    // Set its color space and background color
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGFloat components[4] = {0.0f, 0.0f, 0.0f, 1.0f};
    CGColorRef bgColor = CGColorCreate(colorSpace, components);
    backingLayer.backgroundColor = bgColor;
    CGColorRelease(bgColor);
    CGColorSpaceRelease(colorSpace);

I should also say that there is an NSTimer timer that is defined in initWithFrame fires off the tick method below 12 times a second:

- (void)tick
{    
// Tell the view that it needs to re-draw itself

    if (running) {  // Go!
       //  NSLog(@"frameRate: %2.1f, frameCount: %d", frameRate, frameCount);
        [self setNeedsDisplay];
        frameCount++;
    } 
}

I've run Instruments on this app. No memory leaks are detected. But when I run Allocations and (a) suspend app with physical button, (b) touch the app icon to make it run again, then I see huge cluster of allocations (~2 GB) --- and CRASH.

-- Jim

See last comment, which I should have put here. Fixed this by setting BOOL running to FALSE when the app enters its inactive state, resetting it to TRUE when it becomes active once again.