presentViewController之后出现黑屏

Question

I got a UIViewController called SecondViewController which loads the photo library using UIImagePickerController. When I select a photo, it should present another view controller called PhotoViewController. To pass the image from SecondViewController to PhotoViewController I use a singleton. Here is the code:

SecondViewController:

@property (strong,nonatomic) UIImagePickerController *libraryPicker;
@property (strong,nonatomic) UIImage *chosenImage;
@property (strong,nonatomic) PhotoViewController *controller;

- (void)viewDidLoad
{
        controller = [PhotoViewController sharedInstance];
        libraryPicker = [[UIImagePickerController alloc] init];
        libraryPicker.delegate = self;
        libraryPicker.allowsEditing = NO;
        libraryPicker.navigationBarHidden = NO;
        libraryPicker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
        [self presentViewController:libraryPicker animated:YES completion:nil];
}

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    chosenImage = [info objectForKey:UIImagePickerControllerOriginalImage];
    controller.photo = chosenImage;
    [libraryPicker dismissViewControllerAnimated:NO completion:nil];
    [self presentViewController:controller animated:YES completion:nil];
}

PhotoViewController:

@property (strong,readwrite) IBOutlet UIImageView *photoView;
@property (strong,readwrite) UIImage *photo;
+ (PhotoViewController *)sharedInstance;

static PhotoViewController *_self;
+ (PhotoViewController*)sharedInstance
{
    if (_self == nil) {
        _self = [[super alloc] init];
    }
    return _self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    photoView.image = photo;
}

So when I choose a pic, the app shows a black screen without errors in debug area. What's wrong?

PS: I'm using Storyboard and ARC

Answer 1

Couple things to note:

• If PhotoViewController is designed in the storyboard, the way that you are instantiating it in sharedInstance is not correct. It is only creating a plain PhotoViewController with none of the Interface Builder objects created.
  • A better approach here, is to connected the scenes for SecondViewController and PhotoViewController with a manual, modal segue in the storyboard. Then in, SecondViewController in didFinishPickingMediaWithInfo , set the photo on PhotoViewController and manually trigger the segue.
• viewDidLoad of PhotoViewController will only be called the first time it's presented, so it's not the right place to set the photo for subsequent launches. Consider viewWillAppear
• Confirm that photoView is connected between the property and the Interface Builder element in the storyboard