关于iOS调用摄像机来获取照片，通常我们都会调用UIImagePickerController来调用系统提供的相机来拍照，这个控件非常好 用。但是有时UIImagePickerController控件无法满足我们的需求，例如我们需要更加复杂的OverlayerView，这时候我们就 要自己构造一个摄像机控件了。

这需要使用AVFoundation.framework这个framework里面的组件了，所以我们先要导入这个头文件，另外还需要的组件官方文档是这么说的：

● An instance of AVCaptureDevice to represent the input device, such as a camera or microphone
● An instance of a concrete subclass of AVCaptureInput to configure the ports from the input device
● An instance of a concrete subclass of AVCaptureOutput to manage the output to a movie file or still image
● An instance of AVCaptureSession to coordinate the data flow from the input to the output

这里我只构造了一个具有拍照功能的照相机，至于录影和录音功能这里就不加说明了。

总结下来，我们需要以下的对象：

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@property (nonatomic, strong)       AVCaptureSession            * session;
//AVCaptureSession对象来执行输入设备和输出设备之间的数据传递
@property (nonatomic, strong)       AVCaptureDeviceInput        * videoInput;
//AVCaptureDeviceInput对象是输入流
@property (nonatomic, strong)       AVCaptureStillImageOutput   * stillImageOutput;
//照片输出流对象，当然我的照相机只有拍照功能，所以只需要这个对象就够了
@property (nonatomic, strong)       AVCaptureVideoPreviewLayer  * previewLayer;
//预览图层，来显示照相机拍摄到的画面
@property (nonatomic, strong)       UIBarButtonItem             * toggleButton;
//切换前后镜头的按钮
@property (nonatomic, strong)       UIButton                    * shutterButton;
//拍照按钮
@property (nonatomic, strong)       UIView                      * cameraShowView;
//放置预览图层的View

我的习惯是在init方法执行的时候创建这些对象，然后在viewWillAppear方法里加载预览图层。现在就让我们看一下代码就清楚了。

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- (void) initialSession
{
    //这个方法的执行我放在init方法里了
    self.session = [[AVCaptureSession alloc] init];
    self.videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:[self frontCamera] error:nil];
    //[self fronCamera]方法会返回一个AVCaptureDevice对象，因为我初始化时是采用前摄像头，所以这么写，具体的实现方法后面会介绍
    self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
    NSDictionary * outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG,AVVideoCodecKey, nil];
    //这是输出流的设置参数AVVideoCodecJPEG参数表示以JPEG的图片格式输出图片
    [self.stillImageOutput setOutputSettings:outputSettings];
     
    if ([self.session canAddInput:self.videoInput]) {
        [self.session addInput:self.videoInput];
    }
    if ([self.session canAddOutput:self.stillImageOutput]) {
        [self.session addOutput:self.stillImageOutput];
    }
     
}

这是获取前后摄像头对象的方法

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

接下来在viewWillAppear方法里执行加载预览图层的方法

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- (void) setUpCameraLayer
{
    if (_cameraAvaible == NO) return;
     
    if (self.previewLayer == nil) {
        self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session];
        UIView * view = self.cameraShowView;
        CALayer * viewLayer = [view layer];
        [viewLayer setMasksToBounds:YES];
         
        CGRect bounds = [view bounds];
        [self.previewLayer setFrame:bounds];
        [self.previewLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
         
        [viewLayer insertSublayer:self.previewLayer below:[[viewLayer sublayers] objectAtIndex:0]];
         
    }
}

注意以下的方法，在viewDidAppear和viewDidDisappear方法中启动和关闭session

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- (void) viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    if (self.session) {
        [self.session startRunning];
    }
}
 
- (void) viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear: animated];
    if (self.session) {
        [self.session stopRunning];
    }
}

接着我们就来实现切换前后镜头的按钮，按钮的创建我就不多说了

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- (void)toggleCamera {
    NSUInteger cameraCount = [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count];
    if (cameraCount > 1) {
        NSError *error;
        AVCaptureDeviceInput *newVideoInput;
        AVCaptureDevicePosition position = [[_videoInput device] position];
         
        if (position == AVCaptureDevicePositionBack)
            newVideoInput = [[AVCaptureDeviceInput alloc] initWithDevice:[self frontCamera] error:&error];
        else if (position == AVCaptureDevicePositionFront)
            newVideoInput = [[AVCaptureDeviceInput alloc] initWithDevice:[self backCamera] error:&error];
        else
            return;
         
        if (newVideoInput != nil) {
            [self.session beginConfiguration];
            [self.session removeInput:self.videoInput];
            if ([self.session canAddInput:newVideoInput]) {
                [self.session addInput:newVideoInput];
                [self setVideoInput:newVideoInput];
            } else {
                [self.session addInput:self.videoInput];
            }
            [self.session commitConfiguration];
        } else if (error) {
            NSLog(@"toggle carema failed, error = %@", error);
        }
    }
}

这是切换镜头的按钮方法

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- (void) shutterCamera
{
    AVCaptureConnection * videoConnection = [self.stillImageOutput connectionWithMediaType:AVMediaTypeVideo];
    if (!videoConnection) {
        NSLog(@"take photo failed!");
        return;
    }
     
    [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {
        if (imageDataSampleBuffer == NULL) {
            return;
        }
        NSData * imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
        UIImage * image = [UIImage imageWithData:imageData];
        NSLog(@"image size = %@",NSStringFromCGSize(image.size));
    }];
}

这是拍照按钮的方法

这样自定义照相机的简单功能就完成了，如果你想要再添加其他复杂的功能，可以参考一下下面这篇文章，希望对你们有所帮助。

http://course.gdou.com/blog/Blog.pzs/archive/2011/12/14/10882.html

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