Animating and removing an NSImageView object failed?

Question

My app situation:
I am now having an app displaying a dynamic picture. And I want to capture its current image and save it to disc.

My goal:
I am working on an animated visual effect: add an image view on top, and then animates it from its origin frame into CGRecrZero. Finally, remove this image view from vie hierarchy after animation is done.

---

Now problem:
First time triggerring the action, it seems work. But when trigger it at the second time, the image view does not animate and stay atop of all subviews.

---

Codes of the view controller(with ARC):

Firstly, this is the IBAction to trigger the snapshot:

- (IBAction)actionSaveSnapshot:(id)sender
{
    ...    // Save the image file. This works everytime.

    NSThread *tempThread = [[NSThread alloc] initWithTarget:self
                                                   selector:@selector(threadSimulateScreenCapture:) 
                                                     object:nil];
    if (tempThread)
    {
        [tempThread start];
        tempThread = nil;     // Simply release it 
    }
}

And here is the thread:

- (void)threadSimulateScreenCapture:(id)arg
{@autoreleasepool {
    NSImageView __strong *subImageView;
    subImageView = [[NSImageView alloc] init];
    NSRect subRect = [_imageView frame];    // the dynamic image view which I want to snapshot with
    const CGFloat animationTime = 0.4;

    [subImageView setWantsLayer:YES];
    [subImageView setImageScaling:NSImageScaleAxesIndependently];
    [subImageView setImage:[_imageView image]];

    dispatch_async(dispatch_get_main_queue(), ^{
        [CATransaction begin];
        [self.view addSubview:subImageView];
        [subImageView setFrame:subRect];
        [subImageView setNeedsDisplay:YES];
        [CATransaction commit];
    });

    [NSThread sleepForTimeInterval:0.01];
    dispatch_async(dispatch_get_main_queue(), ^{
        [CATransaction begin];
        [CATransaction setAnimationDuration:animationTime];
        [subImageView.layer setFrame:CGRectZero];
        [CATransaction commit];
    });

    [NSThread sleepForTimeInterval:(NSTimeInterval)animationTime];    // wait for end of animation

    dispatch_async(dispatch_get_main_queue(), ^{
        [subImageView removeFromSuperview];
    });

    NSLog(@"SubView Count: %@\n%@", self.view.subviews, subImageView);  // MARK. described below
    subImageView = nil;    // release the image
}} // ENDS: thread and aotureleasepool

Every time the program runs to the "MARK" line and print the subview array, it is clear thar the subImageView is not removed from superview then. And every time the thread ends, a "deleted thread with uncommitted CATransaction ...." raised.

What wrong did I do?

Answer 1

I may solved my own problem: At the line with [subImageView setFrame:subRect];, insert another line with: [subImageView.layer setFrame:subRect];

Meanwhile, add another line before the "addSubview:" method: [self.view setWantsLayer:YES];.

It seemed work. But I do not know why. Why I should set both view and layer's frame?