1、首先声明以下对象

#import //捕获设备，通常是前置摄像头，后置摄像头，麦克风（音频输入）@property (nonatomic, strong) AVCaptureDevice *device;//AVCaptureDeviceInput 代表输入设备，他使用AVCaptureDevice 来初始化@property (nonatomic, strong) AVCaptureDeviceInput *input;//输出图片@property (nonatomic ,strong) AVCaptureStillImageOutput *imageOutput;//session：由他把输入输出结合在一起，并开始启动捕获设备（摄像头）@property (nonatomic, strong) AVCaptureSession *session;//图像预览层，实时显示捕获的图像@property (nonatomic ,strong) AVCaptureVideoPreviewLayer *previewLayer;

2、初始化各个对象

- (void)cameraDistrict{// AVCaptureDevicePositionBack 后置摄像头// AVCaptureDevicePositionFront 前置摄像头 self.device = [self cameraWithPosition:AVCaptureDevicePositionFront]; self.input = [[AVCaptureDeviceInput alloc] initWithDevice:self.device error:nil]; self.imageOutput = [[AVCaptureStillImageOutput alloc] init]; self.session = [[AVCaptureSession alloc] init]; //  拿到的图像的大小可以自行设定 // AVCaptureSessionPreset320x240 // AVCaptureSessionPreset352x288 // AVCaptureSessionPreset640x480 // AVCaptureSessionPreset960x540 // AVCaptureSessionPreset1280x720 // AVCaptureSessionPreset1920x1080 // AVCaptureSessionPreset3840x2160 self.session.sessionPreset = AVCaptureSessionPreset640x480; //输入输出设备结合 if ([self.session canAddInput:self.input]) {  [self.session addInput:self.input]; } if ([self.session canAddOutput:self.imageOutput]) {  [self.session addOutput:self.imageOutput]; } //预览层的生成 self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session]; self.previewLayer.frame = CGRectMake(0, 64, SCREEN_WIDTH, SCREEN_HEIGHT-64); self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill; [self.view.layer addSublayer:self.previewLayer]; //设备取景开始 [self.session startRunning]; if ([_device lockForConfiguration:nil]) { //自动闪光灯，  if ([_device isFlashModeSupported:AVCaptureFlashModeAuto]) {   [_device setFlashMode:AVCaptureFlashModeAuto];  }  //自动白平衡,但是好像一直都进不去  if ([_device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeAutoWhiteBalance]) {   [_device setWhiteBalanceMode:AVCaptureWhiteBalanceModeAutoWhiteBalance];  }  [_device unlockForConfiguration]; }}

根据前后置位置拿到相应的摄像头：

- (AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition)position{ NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]; for ( AVCaptureDevice *device in devices )  if ( device.position == position ){   return device;  } return nil;}

3、拍照拿到相应图片：

- (void)photoBtnDidClick{ AVCaptureConnection *conntion = [self.imageOutput connectionWithMediaType:AVMediaTypeVideo];  if (!conntion) {   NSLog(@"拍照失败!");   return;   } [self.imageOutput captureStillImageAsynchronouslyFromConnection:conntion completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {  if (imageDataSampleBuffer == nil) {   return ;   }  NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];  self.image = [UIImage imageWithData:imageData];  [self.session stopRunning];  [self.view addSubview:self.cameraImageView];}

4、保存照片到相册：

#pragma - 保存至相册- (void)saveImageToPhotoAlbum:(UIImage*)savedImage{ UIImageWriteToSavedPhotosAlbum(savedImage, self, @selector(image:didFinishSavingWithError:contextInfo:), NULL);}// 指定回调方法- (void)image: (UIImage *) image didFinishSavingWithError: (NSError *) error contextInfo: (void *) contextInfo{ NSString *msg = nil ; if(error != NULL){  msg = @"保存图片失败" ; }else{  msg = @"保存图片成功" ; } UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"保存图片结果提示"           message:msg           delegate:self           cancelButtonTitle:@"确定"           otherButtonTitles:nil]; [alert show];}

5、前后置摄像头的切换

- (void)changeCamera{ NSUInteger cameraCount = [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count]; if (cameraCount > 1) {  NSError *error;  //给摄像头的切换添加翻转动画  CATransition *animation = [CATransition animation]；  animation.duration = .5f；  animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];  animation.type = @"oglFlip";  AVCaptureDevice *newCamera = nil;  AVCaptureDeviceInput *newInput = nil; //拿到另外一个摄像头位置  AVCaptureDevicePosition position = [[_input device] position];  if (position == AVCaptureDevicePositionFront){   newCamera = [self cameraWithPosition:AVCaptureDevicePositionBack];   animation.subtype = kCATransitionFromLeft;//动画翻转方向  }  else {   newCamera = [self cameraWithPosition:AVCaptureDevicePositionFront];   animation.subtype = kCATransitionFromRight;//动画翻转方向  }  //生成新的输入  newInput = [AVCaptureDeviceInput deviceInputWithDevice:newCamera error:nil];  [self.previewLayer addAnimation:animation forKey:nil];  if (newInput != nil) {   [self.session beginConfiguration];   [self.session removeInput:self.input];   if ([self.session canAddInput:newInput]) {    [self.session addInput:newInput];    self.input = newInput;   } else {    [self.session addInput:self.input];   }   [self.session commitConfiguration];  } else if (error) {   NSLog(@"toggle carema failed, error = %@", error);  } }}

6、相机的其它参数设置

//AVCaptureFlashMode 闪光灯//AVCaptureFocusMode 对焦//AVCaptureExposureMode 曝光//AVCaptureWhiteBalanceMode 白平衡//闪光灯和白平衡可以在生成相机时候设置//曝光要根据对焦点的光线状况而决定,所以和对焦一块写//point为点击的位置- (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]) {  //对焦模式和对焦点  if ([self.device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {   [self.device setFocusPointOfInterest:focusPoint];   [self.device setFocusMode:AVCaptureFocusModeAutoFocus];  }  //曝光模式和曝光点  if ([self.device isExposureModeSupported:AVCaptureExposureModeAutoExpose ]) {   [self.device setExposurePointOfInterest:focusPoint];   [self.device setExposureMode:AVCaptureExposureModeAutoExpose];  }  [self.device unlockForConfiguration];  //设置对焦动画  _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;   }];  }]; }}

7、遇到的一些坑和解决办法

1) 前后置摄像头的切换

前后值不能切换，各种尝试找了半天没找到有原因。后来发现我在设置图片尺寸的时候设置为1080P [self.session canSetSessionPreset: AVCaptureSessionPreset1920x1080] ，前置摄像头并不支持这么大的尺寸，所以就不能切换前置摄像头。我验证了下 前置摄像头最高支持720P,720P以内可自由切换。　　

当然也可以在前后置摄像头切换的时候，根据前后摄像头来设置不同的尺寸，这里不在赘述。

2）焦点位置

CGPoint focusPoint = CGPointMake( point.y /size.height ,1-point.x/size.width );setExposurePointOfInterest：focusPoint 函数后面Point取值范围是取景框左上角（0，0）到取景框右下角（1，1）之间。官方是这么写的：

　　The value of this property is a CGPoint that determines the receiver's focus point of interest, if it has one. A value of (0,0) indicates that the camera should focus on the top left corner of the image, while a value of (1,1) indicates that it should focus on the bottom right. The default value is (0.5,0.5).

我也试了按这个来但位置就是不对，只能按上面的写法才可以。前面是点击位置的y/PreviewLayer的高度，后面是1-点击位置的x/PreviewLayer的宽度

3）对焦和曝光

　　我在设置对焦是 先设置了模式setFocusMode，后设置对焦位置，就会导致很奇怪的现象，对焦位置是你上次点击的位置。所以一定要先设置位置，再设置对焦模式。　　曝光同上