UIViewAnimation从dispatch_after阻塞UIViewAnimation完成块

Question

我有以下设想：

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

和

-(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方法类似于：

+ (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);
 }

因此，发出，每当从dispatch_after_delta调用animation方法时，animation方法never gets its completion block。

什么是可能的解决办法？

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

而不是因为你提交了块

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

对于主队列，并且主队列是一个串行队列，所以动画完成块要到上面的块返回时才会执行。

要解决这个问题，您可以：

1. 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);
2. 在主队列中执行动画： dispatch_async(dispatch_get_main_queue()，^{ UIView动画:持续时间动画：^ view.center =CGPointMake(view.cent.x，view.cent.y+ length)；}完成：^(BOOL已完成){ //如果我从dispatch_after调用此方法，则永远不会发生这种情况。已完成=否；}； })；

在我看来，最好不要在分派块中显式地使用NSThread和NSRunLoop。