Question

在我的应用程序中，我有一个音乐播放器，实际上是来自iTunes的歌曲并播放预览。但是因为AVAudio播放器需要将文件写入本地文件才能播放。因此，有时单击我的播放按钮需要2-3秒，所以我想在我的按钮上显示UIActivityIndicator视图，以便用户知道它的加载。

我知道如何为其他视图加载做到这一点，但是这里一个接一个地发生在一个方法中，所以不知道怎么做。

这是我的代码：

wait = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
        UIView * temp = (UIView *)sender;
        [temp addSubview:wait];
        [wait startAnimating];
        NSError * error;
        int tag = [sender tag]-100;
        previousTag = sender;
        active = sender;
        UIButton * button = (UIButton *)sender;
        [UIView transitionWithView:button
                          duration:0.5
                           options:UIViewAnimationOptionTransitionFlipFromLeft 
                        animations:^{ 
                            [button setBackgroundImage:pauseButtonImage.image forState:UIControlStateNormal];
                        }
                        completion:NULL];
        NSIndexPath * indexPath = [NSIndexPath indexPathForRow:tag inSection:0];
        [songsResults selectRowAtIndexPath:indexPath animated:YES scrollPosition:UITableViewScrollPositionNone];

        NSString * floatPath = [NSString stringWithFormat:@"preview%d",tag];
        NSString *uniquePath = [TMP stringByAppendingPathComponent: floatPath];
            if([[NSFileManager defaultManager] fileExistsAtPath: uniquePath])
            {
                [wait stopAnimating];
                audioPlayer = [[AVAudioPlayer alloc]initWithContentsOfURL:[NSURL fileURLWithPath:uniquePath] error:&error];
            }
            else {

            NSArray * temp = [dataToDisplay objectAtIndex:tag];
            NSString * urlString = [temp objectAtIndex:3];
            NSURL *url = [NSURL URLWithString:urlString];
            NSData *soundData = [NSData dataWithContentsOfURL:url];

            [soundData writeToFile:uniquePath atomically:YES];
                [wait stopAnimating];
            audioPlayer = [[AVAudioPlayer alloc]initWithContentsOfURL:[NSURL fileURLWithPath:uniquePath] error:&error];
            }
        float duration = [audioPlayer duration];

        timer = [NSTimer scheduledTimerWithTimeInterval:duration target:self selector:@selector(stopPreview:) userInfo:nil repeats:NO];
            [audioPlayer play];
            isPlaying = YES;
    }

Answer 1

通过调用performSelectorInBackground让阻止任务在后台运行。并且为了在任务完成时得到通知，要么传递一个块，要么使用一个代表。

FileStorage.h

@protocol FileStorageDelegate <NSObject>
- (void)fileStorageDidWriteToFile;
@end

@interface FileStorage

@property (nonatomic, assign) id <FileStorageDelegate> delegate;

@end

FileStorage.m

@implementation FileStorage
@synthesize delegate = _delegate;

- (void)storeFile:(NSData *)data
{
   [self performSelectorInBackground:@selector(storeFileInBackground:) withObject:data];
}

- (void)storeFileInBackground:(NSData *)data
{
   // perfofm blocking task


   // Call delegate and pass some parameters if needed
   [self.delegate fileStorageDidWriteToFile];
}

@end

如何停止操作以执行下一个操作？

1 个答案: