二维码识别(相对完整，可以缩放)

不积跬步，无以至千里；不积小流，无以成江海

---

在生活中随处可见二维码，特别是支付宝支付和微信支付把二维码推向了高潮。现在在项目也要添加二维码扫描功能

初期规划的功能只是扫描墙上或者设备上的二维码，所以也只做了最简单的二维码扫描。

后来在实际使用过程中发现有其他场景，比如：在大屏幕上有个二维码，你坐在座位上扫的时候发现扫不上。这时候就需要扫描范围放大来识别二维码。

对标微信的扫一扫，可能没有那么好的性能，但是功能上可以是一致的

双击放大：

-(void)handleDoubleTap:(UITapGestureRecognizer *)recogniser {
    if (!_device)
        return;
    if (recogniser.state == UIGestureRecognizerStateBegan)
    {
        _initialPinchZoom = _device.videoZoomFactor;
    }
    NSError *error = nil;
    [_device lockForConfiguration:&error];
    if (!error) {
        CGFloat zoomFactor;
        if (_device.videoZoomFactor == 1.0f) {
            zoomFactor = _maxZoom;
        }
        else{
            zoomFactor = 1.0f;
        }
        _device.videoZoomFactor = zoomFactor;
        [_device unlockForConfiguration];
    }
}

两指缩放：

- (void)pinchDetected:(UIPinchGestureRecognizer *)recogniser {
    if (!_device)
        return;
    if (recogniser.state == UIGestureRecognizerStateBegan)
    {
        _initialPinchZoom = _device.videoZoomFactor;
    }
    
    NSError *error = nil;
    [_device lockForConfiguration:&error];
    
    if (!error) {
        CGFloat zoomFactor;
        CGFloat scale = recogniser.scale;
        zoomFactor = scale * _initialPinchZoom;
        zoomFactor = MIN(_maxZoom, zoomFactor);
        zoomFactor = MAX(1.0f, zoomFactor);
        _device.videoZoomFactor = zoomFactor;
        [_device unlockForConfiguration];
        NSLog(@"%f",_device.videoZoomFactor);
    }
}

单击屏幕对焦：

//手动对焦
- (void)focusGesture:(UITapGestureRecognizer*)gesture{
    CGPoint point = [gesture locationInView:gesture.view];
    [self focusAtPoint:point];
}
- (void)focusAtPoint:(CGPoint)point{
    CGSize size = self.view.bounds.size;
    CGPoint focusPoint = CGPointMake( point.y /size.height ,1-point.x/size.width );
    NSError *error;
    if ([self.device lockForConfiguration:&error]) {
        
        if ([self.device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
            [self.device setFocusPointOfInterest:focusPoint];
            [self.device setFocusMode:AVCaptureFocusModeAutoFocus];
        }
        
        if ([self.device isExposureModeSupported:AVCaptureExposureModeAutoExpose ]) {
            [self.device setExposurePointOfInterest:focusPoint];
            [self.device setExposureMode:AVCaptureExposureModeAutoExpose];
        }
        
        [self.device unlockForConfiguration];
        _focusView.center = point;
        _focusView.hidden = NO;
        [UIView animateWithDuration:0.3 animations:^{
            _focusView.transform = CGAffineTransformMakeScale(1.25, 1.25);
        }completion:^(BOOL finished) {
            [UIView animateWithDuration:0.5 animations:^{
                _focusView.transform = CGAffineTransformIdentity;
            } completion:^(BOOL finished) {
                _focusView.hidden = YES;
            }];
        }];
    }
}

注意：

在点击对焦后，它锁定你点击的焦点对焦，锁定当前焦距，摄像头切换到其他地方，发现变模糊了，这是因为还是之前的焦距。这时候需要监听摄像头位置改变“AVCaptureDeviceSubjectAreaDidChangeNotification”，将摄像头切换为连续对焦模式。
1.打开设备的监听

device.subjectAreaChangeMonitoringEnabled=YES;

2.添加通知

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(subjectAreaDidChange:)name:AVCaptureDeviceSubjectAreaDidChangeNotification object:self.device];

3.修改对焦模式

- (void)subjectAreaDidChange:(NSNotification *)notification
{
    if (_device.focusMode == AVCaptureFocusModeContinuousAutoFocus) {
        return;
    }
    //先进行判断是否支持控制对焦
    if (_device.isFocusPointOfInterestSupported &&[_device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
        NSError *error =nil;
        //对cameraDevice进行操作前，需要先锁定，防止其他线程访问，
        [_device lockForConfiguration:&error];
        //自动对焦
        [_device setFocusMode:AVCaptureFocusModeContinuousAutoFocus];
        [_device setFocusPointOfInterest:CGPointMake(0.5, 0.5)];
        //自动曝光
        [_device setExposureMode:(AVCaptureExposureModeContinuousAutoExposure)];
        [_device setExposurePointOfInterest:CGPointMake(0.5, 0.5)];
        //        [self focusAtPoint:CGPointMake(ScreenWidth/2, ScreenHeight/2 - 32.5*SCALE)];
        //操作完成后，记得进行unlock。
        [_device unlockForConfiguration];
    }
}

总结：

这样一个具有缩放功能的二维码扫描基本完善了。微信的扫一扫可以自动识别二维码，并放大识别，对焦后也更加流畅。这就是我们和微信的差距吧。
最后放上git地址：https://github.com/famile/QRCodeScanDemo

---

跑得慢，听到的是骂声； 跑得快，听到的就只是风声

---