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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