iOS：如何让 ViewController A 模态呈现 B，然后让 B 直接关闭/转换到模态呈现的 C？答案

【问题标题】：iOS: How can I have ViewController A present B modally and then have B dismiss/transition directly to a modally presented C?iOS：如何让 ViewController A 模态呈现 B，然后让 B 直接关闭/转换到模态呈现的 C？
【发布时间】：2013-06-18 05:36:20
【问题描述】：

现在我有一个 ViewController（“A”），它以模态方式呈现用户的 iPod 库（“B”）：

// This works great
- (void)selectSong { // UIBarButtonSystemItemAdd target action
    MPMediaPickerController *picker = [[MPMediaPickerController alloc] init];
    picker.delegate = self;
    [self presentViewController:picker animated:YES completion:NULL];
}

我通过委托从“A”中解散模态呈现的 VC，“B”：

- (void)mediaPicker:(MPMediaPickerController *)mediaPicker didPickMediaItems:(MPMediaItemCollection *)mediaItemCollection {
    // Do stuff with selected item...

    // Set up modal transition style and then dismiss
    [mediaPicker setModalTransitionStyle:UIModalTransitionStyleFlipHorizontal];
    [mediaPicker dismissViewControllerAnimated:YES completion:^{
        // Launch capture screen
        // DOING IT THIS WAY CLEARLY SHOWS VIEW "A" BEFORE WE SEE VIEW "C"
        // I'M LOOKING FOR A WAY I CAN DISMISS THE MODAL IPOD MUSIC PICKER
        // VIA "FLIP" DIRECTLY TO VIEW CONTROLLER "C" (WHICH DOES SOMETHING
        // WITH THE SELECTED SONG).
        [self performSegueWithIdentifier:@"captureViewController" sender:self];
    }];
}

有了这个实现，技术上一切正常。我不喜欢的是 ViewController A 呈现 B 和 C 的方式，用户可以在它解除 B 之后和呈现 C 之前看到 ViewController A。我希望 A 呈现 B 然后 B 直接解除/过渡到C. 我怎样才能做到这一点？

*更新：另请注意，如果我将手动 segue 调用放在完成块之外，那么我会收到关于同时呈现两件事的错误。如果我将动画切换为 NO，我会得到一个不同的错误。

【问题讨论】：

标签： iphone ios objective-c

【解决方案1】：

在情节提要中给captureViewController 一个标识符。

- (void)mediaPicker:(MPMediaPickerController *)mediaPicker didPickMediaItems:(MPMediaItemCollection *)mediaItemCollection {
    // Do stuff with selected item...

    // Set up modal transition style and then dismiss

    UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"STORYBOARDNAME" bundle:nil];
    UIViewController *vc = [mainStoryboard instantiateViewControllerWithIdentifier:@"captureViewController"];
    [self presentModalViewController:vc animated:NO];

    [mediaPicker setModalTransitionStyle:UIModalTransitionStyleFlipHorizontal];
    [mediaPicker dismissViewControllerAnimated:YES completion:nil];
}

【讨论】：

这看起来很有希望。我试了一下，收到以下错误消息：Warning: Attempt to present <CaptureViewController: 0x1c5affb0> on <UINavigationController: 0x1d83af60> whose view is not in the window hierarchy!

【解决方案2】：

试试这个，

- (void)selectSong { // UIBarButtonSystemItemAdd target action
    MPMediaPickerController *picker = [[MPMediaPickerController alloc] init];
    picker.delegate = self;
 [self performSegueWithIdentifier:@"captureViewController" sender:self];
    }];
    [self presentViewController:picker animated:YES completion:NULL];
}

【讨论】：

这种方法将 captureViewController 放在 iPod 歌曲选择器之前的屏幕上。用户永远没有机会选择歌曲。