为什么我的自定义相机界面中显示的预览与iOS开发中系统相机中显示的预览不一样？

Question

self.device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
self.input = [[AVCaptureDeviceInput alloc]initWithDevice:self.device error:nil];
self.videoOutPut = [[AVCaptureVideoDataOutput alloc]init];
[self.videoOutPut setSampleBufferDelegate:self queue:dispatch_get_global_queue(0, 0)];
_ImageOutPut = [[AVCapturePhotoOutput alloc]init];
self.session = [[AVCaptureSession alloc]init];
if ([self.session canSetSessionPreset:AVCaptureSessionPreset1920x1080]) {
    [self.session setSessionPreset:AVCaptureSessionPreset1920x1080];
}
if ([self.session canAddInput:self.input]) {
    [self.session addInput:self.input];
}
if ([_session canAddOutput:_ImageOutPut]) {
    [_session addOutput:_ImageOutPut];
}
if ([_session canAddOutput:self.videoOutPut]) {
    [_session addOutput:self.videoOutPut];
}
self.previewLayer = [[AVCaptureVideoPreviewLayer alloc]initWithSession:self.session];
self.previewLayer.frame = CGRectMake(0, 0, ScreenWidth, ScreenHeight - 164);
self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[self.view.layer addSublayer:self.previewLayer];
[self.session startRunning];
if ([self.device lockForConfiguration:nil]) {
    if ([self.device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeAutoWhiteBalance]) {
        [self.device setWhiteBalanceMode:AVCaptureWhiteBalanceModeAutoWhiteBalance];
    }
    [self.device unlockForConfiguration];
}

为什么我的自定义相机界面中显示的预览与iOS开发中系统相机中显示的预览不一样？ 以上是我设置的代码，我应该怎么做才能显示更多的内容在此处输入图像描述