问iOS 7 UIImagePickerController相机无图像

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NSString *mediaType = AVMediaTypeVideo; // Or AVMediaTypeAudio

AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:mediaType];

// This status is normally not visible—the AVCaptureDevice class methods for discovering devices do not return devices the user is restricted from accessing.
if(authStatus == AVAuthorizationStatusRestricted){
    NSLog(@"Restricted");
}

// The user has explicitly denied permission for media capture.
else if(authStatus == AVAuthorizationStatusDenied){
    NSLog(@"Denied");
}

// The user has explicitly granted permission for media capture, or explicit user permission is not necessary for the media type in question.
else if(authStatus == AVAuthorizationStatusAuthorized){
    NSLog(@"Authorized");
}

// Explicit user permission is required for media capture, but the user has not yet granted or denied such permission.
else if(authStatus == AVAuthorizationStatusNotDetermined){

    [AVCaptureDevice requestAccessForMediaType:mediaType completionHandler:^(BOOL granted) {

        // Make sure we execute our code on the main thread so we can update the UI immediately.
        //
        // See documentation for ABAddressBookRequestAccessWithCompletion where it says
        // "The completion handler is called on an arbitrary queue."
        //
        // Though there is no similar mention for requestAccessForMediaType, it appears it does
        // the same thing.
        //
        dispatch_async(dispatch_get_main_queue(), ^{

            if(granted){
                // UI updates as needed
                NSLog(@"Granted access to %@", mediaType);
            }
            else {
                // UI updates as needed
                NSLog(@"Not granted access to %@", mediaType);
            }
        });

    }];

}

else {
    NSLog(@"Unknown authorization status");
}

AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
if (authStatus == AVAuthorizationStatusAuthorized) {
    // successful
} else {
    // failed, such as
    // AVAuthorizationStatusNotDetermined
    // AVAuthorizationStatusRestricted
    // AVAuthorizationStatusNotDetermined
}

if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0) {
    // code for AVCaptureDevice auth checking
}