MPMediaPicker不显示

Question

在我为Apple设计的示例应用程序中，无法显示MPMediaPickerController。

我已经在info.plist文件中添加了NSAppleMusicUsageDescription键，这使我的帖子与在线找到的其他答案有所不同。

我还尝试添加CoreMedia.framework。

我正在使用XCode 10 beta 4

该应用程序从不要求访问媒体库的权限，当我显示选择器时，会立即调用mediaPickerDidCancel方法。

我在做什么错了？

感谢您的帮助！

头文件：

#import <UIKit/UIKit.h>
#import <MediaPlayer/MPMediaPickerController.h>

@interface ViewController : UIViewController<MPMediaPickerControllerDelegate>

@end

obj文件：

#import "ViewController.h"
#import <MediaPlayer/MediaPlayer.h>

@interface ViewController ()

@end

@implementation ViewController {
    MPMediaPickerController *picker;
}

- (void)viewDidLoad {
    [super viewDidLoad];
}

- (IBAction)selectButtonPressed:(id)sender {

    picker = [[MPMediaPickerController alloc] initWithMediaTypes: MPMediaTypeAnyAudio];
    [picker setDelegate: self];
    [picker setAllowsPickingMultipleItems: NO];
    picker.prompt = @"Select a Song.";

    UIViewController *rootController = [UIApplication sharedApplication].keyWindow.rootViewController;

    [rootController presentViewController:picker animated:YES completion:^{
        NSLog(@"Complete!");
    }];
}

- (void) mediaPicker: (MPMediaPickerController *) mediaPicker didPickMediaItems: (MPMediaItemCollection *) collection {

    MPMediaItem *firstItem;
    for (MPMediaItem *item in collection.items) {
        firstItem = item;
        break;
    }

    MPMusicPlayerController *samplePlayer  = [MPMusicPlayerController applicationMusicPlayer];
    [samplePlayer setShuffleMode: MPMusicShuffleModeOff];
    [samplePlayer setRepeatMode: MPMusicRepeatModeOne];
    [samplePlayer beginGeneratingPlaybackNotifications];

    // self.mediaItem chosen using MPMediaPickerController
    [samplePlayer setQueueWithItemCollection:[[MPMediaItemCollection alloc] initWithItems:@[firstItem]]];
    [samplePlayer prepareToPlay];

    // Assume that song is at least 120 seconds long
    [samplePlayer play];
}

#pragma mark - delegate methods and segues

- (void) mediaPickerDidCancel: (MPMediaPickerController *) mediaPicker {
    [self dismissViewControllerAnimated:true completion:^{
    }];
}
@end