在做扫码需求，往往会有放大镜头需求。

苹果提供了AVCaptureConnection中，videoScaleAndCropFactor：缩放裁剪系数,使用该属性，可以实现拉近拉远镜头。再结合手势UIPinchGestureRecognizer，就很简单实现手势拉近拉远镜头。

手势代码

///记录开始的缩放比例
@property(nonatomic,assign)CGFloat beginGestureScale;

///最后的缩放比例
@property(nonatomic,assign)CGFloat effectiveScale;

- (void)cameraInitOver
{
 if (self.isVideoZoom) {
  UIPinchGestureRecognizer *pinch = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchDetected:)];
  pinch.delegate = self;
  [self.view addGestureRecognizer:pinch];
 }
}

- (void)pinchDetected:(UIPinchGestureRecognizer*)recogniser
{
 self.effectiveScale = self.beginGestureScale * recogniser.scale;
 if (self.effectiveScale < 1.0){
  self.effectiveScale = 1.0;
 }
 [self.scanObj setVideoScale:self.effectiveScale];

}

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
{
 if ( [gestureRecognizer isKindOfClass:[UIPinchGestureRecognizer class]] ) {
  _beginGestureScale = _effectiveScale;
 }
 return YES;
}

拉近拉远镜头代码

- (void)setVideoScale:(CGFloat)scale
{
 [_input.device lockForConfiguration:nil];

 AVCaptureConnection *videoConnection = [self connectionWithMediaType:AVMediaTypeVideo fromConnections:[[self stillImageOutput] connections]];
 CGFloat maxScaleAndCropFactor = ([[self.stillImageOutput connectionWithMediaType:AVMediaTypeVideo] videoMaxScaleAndCropFactor])/16;

 if (scale > maxScaleAndCropFactor)
  scale = maxScaleAndCropFactor;

 CGFloat zoom = scale / videoConnection.videoScaleAndCropFactor;

 videoConnection.videoScaleAndCropFactor = scale;

 [_input.device unlockForConfiguration];

 CGAffineTransform transform = _videoPreView.transform;
 [CATransaction begin];
 [CATransaction setAnimationDuration:.025];

  _videoPreView.transform = CGAffineTransformScale(transform,zoom,zoom);

 [CATransaction commit];

}

有一点需要注意：the videoScaleAndCropFactor property may be set to a value in the range of 1.0 to videoMaxScaleAndCropFactor，videoScaleAndCropFactor这个属性取值范围是1.0-videoMaxScaleAndCropFactor，如果你设置超出范围会崩溃哦！

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