Question

我有以下情况：

dispatch_after_delta(0.1, ^{
    [self checkForTodaysBonus];  // It contains animation methods.
});

并且

-(void) checkForTodaysBonus {
     // Prepare View and other data and then animate UIView
     [Animations moveDown:self.view andAnimationDuration:0.3 andWait:YES andLength:self.view.frame.size.height];
}

其中，moveDown方法如下：

+ (void) moveDown: (UIView *)view andAnimationDuration: (float) duration andWait:(BOOL) wait andLength:(float) length{
    __block BOOL done = wait; //wait =  YES wait to finish animation
    [UIView animateWithDuration:duration animations:^{
        view.center = CGPointMake(view.center.x, view.center.y + length);

    } completion:^(BOOL finished) {
         // This never happens if I call this method from dispatch_after. 
         done = NO;
    }];
    // wait for animation to finish
    // This loop will allow wait to complete animation
      while (done == YES) {  // Application unable to break this condition
         [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.01]];
       }
}

和

 void dispatch_after_delta(float delta, dispatch_block_t block){
       dispatch_after(dispatch_time(DISPATCH_TIME_NOW, delta * NSEC_PER_SEC), dispatch_get_main_queue(), block);
 }

所以，问题，只要从animation，dispatch_after_delta方法animation调用never gets its completion block方法。

什么是可能的解决方案？

Answer 1

我给你的建议是使用performSelector: withObject: afterDelay:。

将当前的dispatch_after替换为：

[self performSelector:@selector(checkForTodaysBonus) withObject:nil afterDelay:1.0f];

Answer 2

比因为你提交了块

^{
   [self checkForTodaysBonus];  // It contains animation methods.
});

到主队列，主队列是一个串行队列，因此动画完成块不会执行，直到上面的块返回。

要解决此问题，您可以：

将块提交到全局队列
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, delta * NSEC_PER_SEC), dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), block);

在主队列中执行动画：

dispatch_async(dispatch_get_main_queue(), ^{
[UIView animateWithDuration:duration animations:^{
    view.center = CGPointMake(view.center.x, view.center.y + length);

} completion:^(BOOL finished) {
    // This never happens if I call this method from dispatch_after.
    done = NO;
}];

}）;

在我看来，您最好不要在调度块中明确使用NSThread和NSRunLoop。

来自dispatch_after的UIViewAnimation阻止UIViewAnimation完成块

2 个答案: