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我有一个由四个轨道组成的队列。当轨道改变时，我想改变一个 UIImage，关于那个特定的轨道（如果轨道 1 正在播放我想显示一个标题为 1.png 的图像，如果轨道 2 正在播放我想显示 2.png 等） .

我想使用 switch 语句，但我不确定在设置表达式时如何使用它。

switch(soundEmotions AVPlayerItem)
    {
        case yellowVoice:

            UIImage * yellowImage = [UIImage imageNamed:@"yellow.png"];
            [UIView transitionWithView:self.view
                              duration:1.0f
                               options:UIViewAnimationOptionTransitionCrossDissolve
                            animations:^{
                                mainImage.image = yellowImage;
                            } completion:NULL];

            break;
        case orangeVoice:

            UIImage * orangeImage = [UIImage imageNamed:@"orange.png"];
            [UIView transitionWithView:self.view
                              duration:1.0f
                               options:UIViewAnimationOptionTransitionCrossDissolve
                            animations:^{
                                mainImage.image = orangeImage;
                            } completion:NULL];

            break;
        case redVoice:

            break;
        case pinkVoice:

            break;
        default:


            break;
    }
4

1 回答 1

2

switch 语句需要一个整数。在这种情况下，您想要的整数是当前正在播放的 AVPlayerItem 的索引。

因此，请保留您将 AVPlayerItems 数组传递给 AVQueuePlayer 的数组的副本。然后在这个数组中找到当前的播放器项目，你就会得到你的索引值。

NSInteger index = [self.soundEmotions indexOfObject:self.player.currentItem];
NSString *imageName = nil;
switch (index) {
    case 0:
        imageName = @"yellow";  // You don't need the ".png" part.
        break:
    case 1:
        imageName = @"orange";
        break:
    case 2:
        imageName = @"red";
        break:
    case 3:
        imageName = @"pink";
        break:
    default:
        // Any other number or NSNotFound.
        break:
}

if (imageName) {
    [UIView transitionWithView:self.view
                      duration:1.0f
                       options:UIViewAnimationOptionTransitionCrossDissolve
                    animations:^{
                        mainImage.image = [UIImage imageNamed:imageName];
                    }
                    completion:NULL];
}

此外，您可以将枚举用于常量以获得更好的可读性。这些只是顺序整数。

typedef enum {
    MyClassPlayerVoiceYellow = 0,
    MyClassPlayerVoiceOrange,
    MyClassPlayerVoiceRed,
    MyClassPlayerVoicePink,
} MyClassPlayerVoice;

然后在交换机中使用它们：

switch (index) {
    case MyClassPlayerVoiceYellow:
        imageName = @"yellow";  // You don't need the ".png" part.
        break:
    case MyClassPlayerVoiceOrange:
        imageName = @"orange";
        break:
    case MyClassPlayerVoiceRed:
        imageName = @"red";
        break:
    case MyClassPlayerVoicePink:
        imageName = @"pink";
        break:
    default:
        break:
}
于 2013-03-11T20:36:26.133 回答