Ios 单击按钮时不拍照

我想用自定义按钮拍照。My

OverLayViewController

是我的控制器，上面有一个按钮，用于执行动作拍照，但它们不单击。并在该行显示警告：

从不可移植指针OverlayViewcontroller strong imagePicker.delegate=overlay分配id nullabel

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在类OverLayViewController中是否采用UIImagePickerController委托协议？在类OverLayViewController中是否采用UIImagePickerController委托协议？

- (void)takePicture
{
    imagePicker=[[UIImagePickerController alloc]init];
    imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
    imagePicker.cameraCaptureMode = UIImagePickerControllerCameraCaptureModePhoto;
    imagePicker.cameraDevice = UIImagePickerControllerCameraDeviceRear;
    imagePicker.showsCameraControls = NO;
    imagePicker.navigationBarHidden = YES;
    imagePicker.toolbarHidden = YES;
    imagePicker.wantsFullScreenLayout = YES;;

    OverLayViewController * overlay =[[OverLayViewController alloc]initWithNibName:@"OverLayViewController" bundle:nil];

    overlay.pickerrefrence = imagePicker;
    imagePicker.cameraOverlayView = overlay.view;
    imagePicker.delegate = overlay;
    [self.view bringSubviewToFront:overlay.view];

    [overlay.button addTarget:self action:@selector(takePicture) forControlEvents:UIControlEventTouchUpInside];
    [self presentViewController:imagePicker animated:YES completion:nil];            
}