iOS 7 UIImagePicker preview black screen

问题:

When i try to load camera from my code, camera preview is black. If I wait for 10-20 seconds it will show real camera preview. I found several questions and some of them suggest that running some other code in background should be the reason for this. However I don't have any code running in background. How should I fix this?

This is my code where I run camera

UIImagePickerController *photoPicker = [[UIImagePickerController alloc] init];

photoPicker.delegate = self;
photoPicker.sourceType = UIImagePickerControllerSourceTypeCamera;
[self presentViewController:photoPicker animated:YES completion:NULL];

回答1:

About 5 months ago my team discovered a memory leak with UIImageViewController in iOS7. Each instantiation slowed down the app exponentially (i.e. first alloc-init had a 1 second delay, second had a 2 second delay, third had a 5 second delay). Eventually, we were having 30-60 delays (similar to what you're experiencing).

We resolved the issue by subclassing UIImagePickerController and making it a Singleton. That way it was only ever initialized once. Now our delay is minimal and we avoid the leak. If subclassing isn't an option, try a class property in your viewController and just lazy load it like so.

-(UIImagePickerController *)imagePicker{
    if(!_imagePicker){
        _imagePicker = [[UIImagePickerController alloc]init];
        _imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
    }
    return _imagePicker;
}

Then you can just call it later like:

[self presentViewController:self.imagePicker animated:YES completion:nil];

回答2:

Had this myself - it happens if something is running on the main dispatch thread - are you resizing images by any chance?

It puts the preview onto the main thread and if something is using it, you get a black screen. It's a bug and the workaround is to either take over the main thread or to disable the photo picker until the queue is free

回答3:

This Should work for you:

    - (void)cameraViewPickerController:(UIImagePickerController *)picker
{
    [self startCameraControllerFromViewController: picker
                                    usingDelegate: self];
}


- (BOOL) startCameraControllerFromViewController: (UIViewController*) controller
                                   usingDelegate: (id <UIImagePickerControllerDelegate,
                                                   UINavigationControllerDelegate>) delegate {

    if (([UIImagePickerController isSourceTypeAvailable:
          UIImagePickerControllerSourceTypeCamera] == NO)
        || (delegate == nil)
        || (controller == nil))
        return NO;


    UIImagePickerController *cameraUI = [[UIImagePickerController alloc] init];
    cameraUI.sourceType = UIImagePickerControllerSourceTypeCamera;

    // Displays a control that allows the user to choose movie capture
    cameraUI.mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeImage, (NSString *) kUTTypeMovie,nil];

    // Hides the controls for moving & scaling pictures, or for
    // trimming movies. To instead show the controls, use YES.
    cameraUI.allowsEditing = NO;

    cameraUI.delegate = delegate;

    [controller presentViewController:cameraUI animated:YES completion:nil];
    return YES;
}