關於iOS調用攝像機來獲取照片，通常我們都會調用UIImagePickerController來調用系統提供的相機來拍照，這個控件非常好用。但是有時UIImagePickerController控件無法滿足我們的需求，例如我們需要更加復雜的OverlayerView，這時候我們就要自己構造一個攝像機控件了。

這需要使用AVFoundation.framework這個framework裡面的組件了，所以我們先要導入這個頭文件，另外還需要的組件官方文檔是這麼說的：

● 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

這裡我只構造了一個具有拍照功能的照相機，至於錄影和錄音功能這裡就不加說明了。

總結下來，我們需要以下的對象：

@property (nonatomic, strong)       AVCaptureSession            * session;
//AVCaptureSession對象來執行輸入設備和輸出設備之間的數據傳遞
@property (nonatomic, strong)       AVCaptureDeviceInput        * videoInput;
//AVCaptureDeviceInput對象是輸入流
@property (nonatomic, strong)       AVCaptureStillImageOutput   * stillImageOutput;
//照片輸出流對象，當然我的照相機只有拍照功能，所以只需要這個對象就夠了
@property (nonatomic, strong)       AVCaptureVideoPreviewLayer  * previewLayer;
//預覽圖層，來顯示照相機拍攝到的畫面
@property (nonatomic, strong)       UIBarButtonItem             * toggleButton;
//切換前後鏡頭的按鈕
@property (nonatomic, strong)       UIButton                    * shutterButton;
//拍照按鈕
@property (nonatomic, strong)       UIView                      * cameraShowView;
//放置預覽圖層的View 

我的習慣是在init方法執行的時候創建這些對象，然後在viewWillAppear方法裡加載預覽圖層。現在就讓我們看一下代碼就清楚了。

- (void) initialSession
{
    //這個方法的執行我放在init方法裡了
    self.session = [[AVCaptureSession alloc] init];
    self.videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:[self frontCamera] error:nil];
    //[self fronCamera]方法會返回一個AVCaptureDevice對象，因為我初始化時是采用前攝像頭，所以這麼寫，具體的實現方法後面會介紹
    self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
    NSDictionary * outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG,AVVideoCodecKey, nil];
    //這是輸出流的設置參數AVVideoCodecJPEG參數表示以JPEG的圖片格式輸出圖片
    [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];
    }
    
}

這是獲取前後攝像頭對象的方法

- (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];
}

接下來在viewWillAppear方法裡執行加載預覽圖層的方法

- (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方法中啟動和關閉session

- (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];
    }
}

接著我們就來實現切換前後鏡頭的按鈕，按鈕的創建我就不多說了

- (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);
        }
    }
}

這是切換鏡頭的按鈕方法

- (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));
    }];
}

這是拍照按鈕的方法

這樣自定義照相機的簡單功能就完成了，如果你想要再添加其他復雜的功能，可以參考一下下面這篇文章，希望對你們有所幫助。

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