Question

I have been trying to us CALayers as “sprites” in an iPhone application I’m working on. From what I have been reading, that seems like the correct thing to do here.

When I setup the layer inside a UIView class I am able to get the layer to show up on the screen:
NSLog(@”GameView initWithCoder”);

NSString* imagePath = [[NSBundle mainBundle] pathForResource:@"earth" ofType:@"png"];
earthImage = [[UIImage alloc] initWithContentsOfFile:imagePath];

earthLayer = [CALayer layer];
[earthLayer setContents:(id)[earthImage CGImage]];
[earthLayer setBounds:CGRectMake(0, 0, 32, 32)];
[earthLayer setPosition:CGPointMake(50, 50)];
[earthLayer setName:@"earth"];

[[self layer] addSublayer:earthLayer];

However, when I attempt to initialize the CALayer outside the UIView, my application crashes:

- (void)loadImage:(NSString*)fileName
{
  NSLog(@"GamePiece loadImage");
  NSArray* fileNameParts = [fileName componentsSeparatedByString:@"."];
  imageName = [[fileNameParts objectAtIndex:0] retain];
  NSString* ext = [fileNameParts objectAtIndex:1];

  NSString* imagePath = [[NSBundle mainBundle] pathForResource:imageName ofType:ext];
  image = [[UIImage alloc] initWithContentsOfFile:imagePath];

  layer = [CALayer layer];
  [layer setContents:(id)[image CGImage]];

  [layer setBounds:CGRectMake(0.0f, 0.0f, 32.0f, 32.0f)];
  [layer setPosition:CGPointMake(50.0f, 50.0f)];
  [layer setName:imageName];

  [fileNameParts release], fileNameParts = nil;
  [ext release], ext = nil;
}

---

NSLog(@"GameView initWithCoder");
earth = [[GamePiece alloc] init];
[earth loadImage:@"earth.png"];

[[self layer] addSublayer:[earth layer]];

Clearly I’m doing something wrong here, but I just don’t know what that would be. I have read the Core Animation Programming Guide and also the iPhone Application Programming Guide, but they really don’t seem to talk about how to initialize a CALayer other than in passing.

I just need a gentle nudge in the correct direction. I have been getting a pretty good understanding about everything else I have learned when it comes to programming the iPhone. I’m just having some issues with Graphics, Layers and Animation.

Thanks in advance!

Answer 1

You don’t own the layer that you get from the layer method, so you have to take ownership. Sometime after your method returns, the layer is being deallocated and that is causing your crash. To cure this:

layer = [[CALayer layer] retain]; // now we explicitly take ownership of this layer

Also, don’t forget to release the layer since you own it now:

// in your dealloc method
[layer release];

You should review the Memory Management Programming Guide for Cocoa for more details on when you own objects and what your responsibilities are regarding memory management.