Question

我想实现这一目标，但我的方法不起作用：

1。用户点击“DoneButton”转到下一个视图控制器。

2。等待动画出现在prepareForSegue开始它的代码之前。

第3。一旦prepareForSegue想要加载下一个视图控制器，就停止/关闭等待的动画。

我的问题： 方法[self startWaitingAnimation];确实被调用，但我想prepareForSegue中的操作会阻塞mainThread，因此我只在prepareForSegue完成时看到动画。但是我希望首先显示动画然后在prepareForSegue中运行代码，并且在下一个View控制器准备就绪后，关闭动画。

我尝试的方法，

使用信号量队列，因此在prepareForSegue内的代码完成后会关闭动画。（没用）
使用dispatch_group。

dispatch_queue_t queue = dispatch_get_global_queue（DISPATCH_QUEUE_PRIORITY_DEFAULT，0）;
dispatch_group_t group = dispatch_group_create（）;

- (void)goToNextVC{
       dispatch_group_async(group, queue, ^{
             [self startWaitingAnimation];
       });
      [self performSegueWithIdentifier:@"filtersAndEdits" sender:self];

}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{          
       if ([[segue identifier] isEqualToString:@"filtersAndEdits"]) {
            dispatch_group_async(_group, _queue, ^{

               AFBlurSegue *blurSegue = (AFBlurSegue *)segue;
               blurSegue.blurRadius = 20;
               blurSegue.tintColor = [UIColor colorWithRed:0/255 green:1/255 blue:0/255 alpha:0.1];
               blurSegue.saturationDeltaFactor = 0.5;

              //Transferring Image Data to FilterAndEdits
              NSMutableArray*finalP =[NSMutableArray arrayWithArray:_drawableView.modifiablePointsArray];

              FiltersAndEdits *FVC = [segue destinationViewController];
              [FVC getFinalPointsArray:finalP];
              [FVC getBgImage: self.image];
              FVC.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;

           });

           dispatch_group_notify(_group, _queue, ^{
              [self stopWaitingAnimation];
           });
    }else if ([[segue identifier] isEqualToString:@"HomeVC"]){
           HomeVC*homeVC = [HomeVC new];
           homeVC=segue.destinationViewController;
           [homeVC setShouldRemoveBlackScreen:YES];
           [homeVC removeBlackTempScreen];
           [self.waitingActivity stopAnimating];
    }            
}`

3.使用NSOperationQueues和NSOperation

     NSOperationQueue * queue = [[NSOperationQueue alloc] init];
     queue.maxConcurrentOperationCount =1;



- (void)goToNextVC{
        self.operationA = [NSBlockOperation blockOperationWithBlock:^{
           [self startWaitingAnimation];
        }];

}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
        self.operationB = [NSBlockOperation blockOperationWithBlock:^{

            AFBlurSegue *blurSegue = (AFBlurSegue *)segue;
            blurSegue.blurRadius = 20;
            blurSegue.tintColor = [UIColor colorWithRed:0/255 green:1/255 blue:0/255 alpha:0.1];
            blurSegue.saturationDeltaFactor = 0.5;

            //Transferring Image Data to FilterAndEdits
            NSMutableArray*finalP =[NSMutableArray arrayWithArray:_drawableView.modifiablePointsArray];

            FiltersAndEdits *FVC = [segue destinationViewController];
            [FVC getFinalPointsArray:finalP];
            [FVC getBgImage: self.image];
            FVC.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
        }];

        self.operationC = [NSBlockOperation blockOperationWithBlock:^{
                [self stopWaitingAnimation];
        }];

        [operationB addDependency:operationA]; 
        [operationC addDependency:operationB];
        [self.queue addOperation:self.operationA];
        [self.queue addOperation:operationB];
        [self.queue addOperation:operationB];
}

我该怎么办？我应该在prepareForSegue方法中使用完成处理程序吗？什么是正确的方法？感谢任何帮助。

Answer 1

使用Dispatch库的Dispatch_after函数我相信它可以解决您的问题：

- (void)goToNextVC{
 //Start the animation
 dispatch_queue_t backgroundQueue;
backgroundQueue = dispatch_queue_create("backgroundQueue", 0);

dispatch_async(backgroundQueue, ^{
    [self startWaitingAnimation];
});
dispatch_async(backgroundQueue, ^{

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int)(700 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [self performSegueWithIdentifier:@"filtersAndEdits" sender:self];
    });
});

}

Answer 2

更新感谢@NisarAhmad，主要是有效，但并非总是如此。

有时它仍然不会让动画运行。它不保证在执行块之前始终显示动画。

- (void)goToNextVC{
     //Start the animation
     [self startWaitingAnimation];

     //Showing animation for 0.7 second.
     dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int)(700 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
         [self performSegueWithIdentifier:@"filtersAndEdits" sender:self];
     });
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{

        if ([[segue identifier] isEqualToString:@"filtersAndEdits"]) {
            //Transferring Image Data to FilterAndEdits
            NSMutableArray*finalP =[NSMutableArray arrayWithArray:_drawableView.modifiablePointsArray];
            FiltersAndEdits *FVC = [segue destinationViewController];
            [FVC getFinalPointsArray:finalP];
            [FVC getBgImage: self.image];
            FVC.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
            AFBlurSegue *blurSegue = (AFBlurSegue *)segue;
            blurSegue.blurRadius = 20;
            blurSegue.tintColor = [UIColor colorWithRed:0/255 green:1/255 blue:0/255 alpha:0.1];
            blurSegue.saturationDeltaFactor = 0.5;

            //Stop the animation.
            [self stopWaitingAnimation];

        }else if ([[segue identifier] isEqualToString:@"HomeVC"]){
            //Other codes related to previous VC
        }
}

如何在prepareForSegue被调用之前执行动画并在它完成时解除？

2 个答案: