当应用程序进入前台时，如何重新启动基于块的动画？答案

【问题标题】：How can I restart my block-based animation when the application comes to the foreground?当应用程序进入前台时，如何重新启动基于块的动画？
【发布时间】：2011-10-06 03:21:55
【问题描述】：

我有以下基于块的动画：

[UIView animateWithDuration:0.5f delay:0.0f 
                    options:UIViewAnimationOptionRepeat|UIViewAnimationOptionAutoreverse|UIViewAnimationOptionAllowUserInteraction|UIViewAnimationOptionCurveEaseInOut
                    animations:^{
                [view.layer setTransform:CATransform3DMakeScale(1.3f, 1.3f, 1.0f)];
                NSLog(@"animating");
                    }completion:^(BOOL finished){
                        NSLog(@"Completed");
                    }];

当应用从后台返回时，将调用完成块，并且我的动画不会重新启动。我尝试使用以下委托方法重新启动动画：

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    /*
     Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
     */
    [[self viewController] animate];
    ......
}

但这并不能恢复动画。

同样，我尝试了这些问题的答案中列出的方法：

但是那里的建议都没有对我有用。当应用程序从后台返回时，还有其他方法可以恢复基于块的 UIView 动画吗？

【问题讨论】：

标签： ios cocoa-touch uiview core-animation

【解决方案1】：

朋友发现问题，需要在视图从后台返回时启用动画

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    /*
     Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
     */
    [UIView enableAnimations:YES];
    [[self viewController] animate];
    ......
}

那么在block动画之前需要removeAllAnimations并设置layer.transform为Identity

hasStarted = YES;
    for(UIButton * button in goldenBreakOutButtons){
        for (UIView* view in button.subviews) {
            if (wasStarted) {
                [view.layer removeAllAnimations];
                view.layer.transform = CATransform3DIdentity;
            }
            if ([view isKindOfClass:[UIImageView class]]) {
                [UIView animateWithDuration:0.5f delay:0.0f 
                        options:UIViewAnimationOptionAutoreverse|UIViewAnimationOptionAllowUserInteraction|UIViewAnimationOptionCurveEaseInOut|UIViewAnimationOptionRepeat
                        animations:^ {
                            [view.layer setTransform:CATransform3DMakeScale(1.3f, 1.3f, 1.0f)];
                            NSLog(@"animating");
                        }
                        completion:^(BOOL finished){
                            if (finished) {
                                NSLog(@"Completed");
                            }

                        }];
            }
        }
    }

【讨论】：

你到底在哪里找到[UIView enableAnimations:YES]？我在任何地方都没有看到这种方法:(
有点晚了，但是试试 [UIView setAnimationsEnabled:YES];

【解决方案2】：

请尝试在 ViewController 中订阅/取消订阅
标准（UIApplicationWillEnterForegroundNotification）通知
来自NSNotificationCenter：

 

    -(void) loadView
    {
    .....
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(restartAnimation)    
                                                 name:UIApplicationWillEnterForegroundNotification 
                                               object:nil];      
    ....
    }
    
    - (void) viewDidUnload
    {
    ...
      [[NSNotificationCenter defaultCenter] removeObserver:self 
                                                      name:UIApplicationWillEnterForegroundNotification 
                                                    object:nil];
    ....
    }
    
    -(void) dealloc
    {
      [[NSNotificationCenter defaultCenter] removeObserver:self];
      [super dealloc];
    }
    
    - (void) restartAnimation
    {
        if(self.logoImageView)
        {
            [logoImageView.layer removeAllAnimations];
            
            CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
    
            animation.fromValue       = [NSNumber numberWithFloat:1.0];
            animation.toValue         = [NSNumber numberWithFloat:0.6];
            animation.duration        = 1.5f;
            animation.timingFunction  = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
            animation.autoreverses    = YES;
            animation.repeatCount     = HUGE_VALF;
            
            [[logoImageView layer] addAnimation:animation forKey:@"hidden"];
        }
    }

【讨论】：

默认情况下它已经订阅，因为 UIApplicationWillEnterForegroundNotification 在应用程序返回前台之前被调用。