iOS開發，呼叫相機iOS7 出現黑屏，iOS8以上正常， 以下為代碼，求大神指教

//调用相机 if (IOS8) { //先设定sourceType为相机，然后判断相机是否可用（ipod）没相机，不可用将sourceType设定为相片库 UIImagePickerControllerSourceType sourceType = UIImagePickerControllerSourceTypeCamera; if (![UIImagePickerController isSourceTypeAvailable: UIImagePickerControllerSourceTypeCamera]) { sourceType = UIImagePickerControllerSourceTypePhotoLibrary; } UIImagePickerController *picker = [[UIImagePickerController alloc] init];//初始化 picker.delegate = self; picker.allowsEditing = YES;//设置可编辑 picker.sourceType = sourceType; [self presentViewController:picker animated:YES completion:^{ }];//进入照相界面 }else { UIImagePickerControllerSourceType sourceType = UIImagePickerControllerSourceTypeCamera; if (![UIImagePickerController isSourceTypeAvailable: UIImagePickerControllerSourceTypeCamera]) { sourceType = UIImagePickerControllerSourceTypePhotoLibrary; } UIImagePickerController *picker = [[UIImagePickerController alloc] init]; picker.delegate = self; picker.allowsEditing = YES; picker.sourceType = sourceType; [self presentModalViewController:picker animated:YES]; }