在viewDidLoad / viewDidAppear的UIView动画？

Question

I am attempting a simple UIView animation in the viewDidLoad or viewDidAppear method but it doesn't animate.

UIImage *bluredScreenshot = [self.parentViewControllerScreenshot applyBlur];

    [UIView transitionWithView:self.screenshotView duration:3.0f options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
        self.screenshotView.image = bluredScreenshot;
    } completion:nil];

Simple cross dissolving two images. When ran from viewDidLoad or viewDidAppear the image changes but isn't animated.

But lets say I run the animation from a method after I press a button, it will animate. Why? Seem strange.

Is it possible to make it from the viewDidLoad method? How would you solve this?

Thanks.

Answer 1

when the view is loading you can't animate because there isn't anything to animate. Try in viewdidapear: and Don't use transition

[UIView animateWithDuration:3.
                      delay:0
                    options:UIViewAnimationOptionTransitionCrossDissolve
                 animations:^{
                             self.screenshotView.image = bluredScreenshot;
                 }
                 completion:nil];

Answer 2

You need to fade in the screenshot. If you're using two images, you'll need to place one image view atop the other. pop this inside viewDidAppear: after calling [super viewDidAppear:animated];

UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.screenshotView.frame];
[self.view addSubview:imageView];
    [imageView setAlpha:0.0f];
    imageView = blurredScreenshot;
    [UIView animateWithDuration:0.3f animations:^{
                [imageView setAlpha:1.0f];
            } completion:^(BOOL finished){
                self.imageView.image = blurredScreenshot;
                [imageView removeFromSuperview];
}];

Answer 3

只是提醒一下，有时你的问题可能是由于没有打电话引起的：

self.layoutIfNeeded()