层移动的UIImageView XY坐标

Question

I move my UIImageView with layer around the screen. When at some point I'm trying to retrieve x and y coordinates of a moved imageView using imageView.frame.origin.x I receive original coordinates not the new ones after the move. How to get X and Y correctly?

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Here is my code:

UIImageView *imageView = [[UIImageView alloc] initWithFrame:rect];  
imageView.animationImages = [NSArray arrayWithArray:imgNameArr];    
imageView.animationDuration = 2;
    imageView.animationRepeatCount = 0;
    [imageView startAnimating];
    [self.view addSubview:imageView];   
CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
pathAnimation.duration = speed;
pathAnimation.calculationMode = kCAAnimationPaced;
pathAnimation.fillMode = kCAFillModeForwards;
pathAnimation.removedOnCompletion = NO; 
CGMutablePathRef pointPath = CGPathCreateMutable();
CGPathMoveToPoint(pointPath, NULL, rect.origin.x, rect.origin.y);
    CGPathAddLineToPoint(pointPath, NULL, x, y);
pathAnimation.path = pointPath;
CGPathRelease(pointPath);   
[imageView.layer addAnimation:pathAnimation forKey:[NSString stringWithFormat:@"pathAnimation%@",objId]];
[imageView release];

Answer 1

Per the UIView documentation for the frame property:

Warning: If the transform property is not the identity transform, the value of this property is undefined and therefore should be ignored.

The frame property also becomes undefined if you adjust that view's layer's transform or affineTransform properties (which are actually what the UIView alters when you set its transform). In Cocoa Touch transforms are applied at the time of compositing by the compositor. At present what you seem to get when a transform is applied is the original frame as though there were no transform, but as the docs say it's undefined so don't rely on that.

If you're just moving the view around with no other transformation, I recommend you use the view's center property rather than applying a transform. That will update your frame correctly. Based on empirical evidence, UIKit also seems smart enough that just adjusting the centre doesn't have any performance downside compared to applying a transform.