UIImagePikerController 浅析

原文链接：http://www.jianshu.com/p/2ac85aca4468

UIImagePickerController是iOS系统提供的和系统的相册和相机交互的一个类,可以用来获取相册的照片,也可以调用系统的相机拍摄照片或者视频。该类的继承结构是:

官方文档中对于该类的说明是:

由于该类继承自UINavgationController,所以在使用过程中一般实现UIImagePickerControllerDelegate和UINavigationControllerDelegate这两个代理，可以利用navgation的push 和pop操作自定义界面实现更复杂的交互效果。下面具体分析该类的一些方法和属性.

属性

  @property(nullable,nonatomic,weak) id <UINavigationControllerDelegate, UIImagePickerControllerDelegate> delegate;

该对象的代理需要实现UINavigationControllerDelegate和UIImagePickerControllerDelegate协议，nullable是xcode6.3之后引入的nullability annotations特性，主要用于在OC和swift之间的转换。这一特性主要包含两个新的类型注释nullable和nonnull，用于表示对象是否可以是NULL或nil(具体内容请参考Xcode特性之nullability annotayions)

@property(nonatomic)  UIImagePickerControllerSourceType     sourceType;  // default value is UIImagePickerControllerSourceTypePhotoLibrary.

sourceType用于指定要访问的系统的媒体类型。UIImagePickerControllerSourceType支持以下3种枚举类型，默认值是图片库

typedef NS_ENUM(NSInteger, UIImagePickerControllerSourceType) {

    UIImagePickerControllerSourceTypePhotoLibrary,

    UIImagePickerControllerSourceTypeCamera,

  UIImagePickerControllerSourceTypeSavedPhotosAlbum

};

PhotoLibrary代表系统照片应用对应的相薄，包含照片流和其它自定义的相册，PhotosAlbum则对应系统照片应用的照片，包含用设备拍摄的所有照片流。Camera则代表相机的摄像头。

 @property(nonatomic,copy)      NSArray<NSString *>  *mediaTypes;

mediaTypes用于设置相机支持的功能，拍照或者是视频，返回值类型可以是kUTTypeMovie,kUTTypeImage

@property(nonatomic)  BOOL  showsCameraControls NS_AVAILABLE_IOS(3_1);

@property(nonatomic)  BOOL  allowsEditing NS_AVAILABLE_IOS(3_1); // replacement for -allowsImageEditing; default value is NO.

@property(nonatomic)  BOOL  allowsImageEditing NS_DEPRECATED_IOS(2_0, 3_1);

showsCameraControls用于指定拍照时下方的工具栏是否显示，allowImageEditing在iOS3.1就已废弃，取而代之的是allowEditing,表示拍完照片或者从相册选完照片后，是否跳转到编辑模式对图片裁剪，只有在showsCameraControls为YES时才有效果。

@property(nonatomic) UIImagePickerControllerCameraCaptureMode cameraCaptureMode NS_AVAILABLE_IOS(4_0); // default is UIImagePickerControllerCameraCaptureModePhoto

@property(nonatomic) UIImagePickerControllerCameraDevice      cameraDevice      NS_AVAILABLE_IOS(4_0); // default is UIImagePickerControllerCameraDeviceRear

@property(nonatomic) UIImagePickerControllerCameraFlashMode   cameraFlashMode

@property(nullable, nonatomic,strong) __kindof UIView  *cameraOverlayView  NS_AVAILABLE_IOS(3_1);   // set a view to overlay the preview view.

@property(nonatomic)   CGAffineTransform    cameraViewTransform NS_AVAILABLE_IOS(3_1);   // set the transform of the preview view.

当sourceType是camera的时候，这几个属性有限，否则抛出异常。cameraCaptureMode捕捉模式指定的是相机是拍摄照片还是视频，它的枚举类型如下:

NS_ENUM(NSInteger, UIImagePickerControllerCameraCaptureMode) {

UIImagePickerControllerCameraCaptureModePhoto,//photo

UIImagePickerControllerCameraCaptureModeVideo//video

};

cameraDevice指定拍摄的摄像头位置，是使用前置摄像头还是后置摄像头,它的枚举类型有:

typedef NS_ENUM(NSInteger, UIImagePickerControllerCameraDevice) {

    UIImagePickerControllerCameraDeviceRear,

    UIImagePickerControllerCameraDeviceFront

};

cameraFlashMode用于指定闪光灯模式，它的枚举类型如下:

typedef NS_ENUM(NSInteger, UIImagePickerControllerCameraFlashMode) {

    UIImagePickerControllerCameraFlashModeOff  = -1,

    UIImagePickerControllerCameraFlashModeAuto = 0,

    UIImagePickerControllerCameraFlashModeOn   = 1

};

cameraViewTransform该结构体可以用于指定拍摄时View的一些形变属性，如旋转缩放等。
当showsCameraControls为NO，系统的工具栏隐藏时，我们可以自定义背景View赋值给cameraOverlayView添加到拍摄时的预览视图之上。

@property(nonatomic)  NSTimeInterval     videoMaximumDuration NS_AVAILABLE_IOS(3_1); // default value is 10 minutes.

@property(nonatomic)  UIImagePickerControllerQualityType    videoQuality NS_AVAILABLE_IOS(3_1);

videoMaximumDuration用于设置视频拍摄模式下最大拍摄时长，默认值是10分钟。 videoQuality表示拍摄的视频质量设置，默认是Medium即表示中等质量。 videoQuality支持的枚举类型如下:

typedef NS_ENUM(NSInteger, UIImagePickerControllerQualityType) {

    UIImagePickerControllerQualityTypeHigh = 0,       // 高清模式

    UIImagePickerControllerQualityTypeMedium = 1,     //中等质量，适于WIFI传播

    UIImagePickerControllerQualityTypeLow = 2,         //低等质量，适于蜂窝网络传输

    UIImagePickerControllerQualityType640x480 NS_ENUM_AVAILABLE_IOS(4_0) = 3,    // VGA 质量

    UIImagePickerControllerQualityTypeIFrame1280x720 NS_ENUM_AVAILABLE_IOS(5_0) = 4,//1280*720的分辨率

    UIImagePickerControllerQualityTypeIFrame960x540 NS_ENUM_AVAILABLE_IOS(5_0) = 5,//960*540分辨率

};

类方法

 @interface UIImagePickerController : UINavigationController   <NSCoding>

+ (BOOL)isSourceTypeAvailable:(UIImagePickerControllerSourceType)sourceType;                 // returns YES if source is available (i.e. camera present)

+ (nullable NSArray<NSString *> *)availableMediaTypesForSourceType:(UIImagePickerControllerSourceType)sourceType; // returns array of available media types (i.e. kUTTypeImage)

+ (BOOL)isCameraDeviceAvailable:(UIImagePickerControllerCameraDevice)cameraDevice                   NS_AVAILABLE_IOS(4_0); // returns YES if camera device is available

+ (BOOL)isFlashAvailableForCameraDevice:(UIImagePickerControllerCameraDevice)cameraDevice           NS_AVAILABLE_IOS(4_0); // returns YES if camera device supports flash and torch.

+ (nullable NSArray<NSNumber *> *)availableCaptureModesForCameraDevice:(UIImagePickerControllerCameraDevice)cameraDevice NS_AVAILABLE_IOS(4_0);

isSourceTypeAvailable用于判断当前设备是否支持指定的sourceType，可以是照片库/相册/相机.
isCameraDeviceAvailable判断当前设备是否支持前置摄像头或者后置摄像头
isFlashAvailableForCameraDevice是否支持前置摄像头闪光灯或者后置摄像头闪光灯
availableMediaTypesForSourceType方法返回所特定的媒体如相册/图片库/相机所支持的媒体类型数组,元素值可以是kUTTypeImage类型或者kUTTypeMovie类型的静态字符串，所以是NSString类型的数组
availableCaptureModesForCameraDevice返回特定的摄像头(前置摄像头/后置摄像头)所支持的拍摄模式数值数组，元素值可以是UIImagePickerControllerCameraCaptureMode枚举里面的video或者photo,所以是NSNumber类型的数组

对象方法

- (void)takePicture NS_AVAILABLE_IOS(3_1);

- (BOOL)startVideoCapture NS_AVAILABLE_IOS(4_0);

- (void)stopVideoCapture  NS_AVAILABLE_IOS(4_0);

takePicture可以用来实现照片的连续拍摄，需要自己自定义拍摄的背景视图来赋值给cameraOverlayView ，结合自定义overlayView实现多张照片的采集，在收到代理的didFinishPickingMediaWithInfo方法之后可以启动额外的捕捉。
startVideoCapture用来判断当前是否可以开始录制视频，当视频正在拍摄中，设备不支持视频拍摄，磁盘空间不足等情况，该方法会返回NO.该方法结合自定义overlayView可以拍摄多部视频
stopVideoCapture当你调用此方法停止视频拍摄时，它会调用代理的imagePickerController：didFinishPickingMediaWithInfo：方法

代理方法

@protocol  UIImagePickerControllerDelegate<NSObject>

@optional

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(nullable NSDictionary<NSString *,id> *)editingInfo NS_DEPRECATED_IOS(2_0, 3_0);

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info;

- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker;

@end

imagePickerController:didFinishPickingImage:editingInfo:在iOS3.0中已废弃，不再使用。当用户取消选取的内容时会调用DidCancel方法，默认实现销毁弹出的视图。当完成内容的选取时会调用didFinishPickingMediaWithInfo方法，默认info字典的key值可以是以下类型:

UIKIT_EXTERN NSString *const UIImagePickerControllerMediaType;      //指定用户选择的媒体类型

UIKIT_EXTERN NSString *const UIImagePickerControllerOriginalImage;  // 原始图片

UIKIT_EXTERN NSString *const UIImagePickerControllerEditedImage;    // 修改后的图片

UIKIT_EXTERN NSString *const UIImagePickerControllerCropRect;       // 裁剪尺寸

UIKIT_EXTERN NSString *const UIImagePickerControllerMediaURL;       // 媒体的URL

UIKIT_EXTERN NSString *const UIImagePickerControllerReferenceURL        NS_AVAILABLE_IOS(4_1);  // 原件的URL

UIKIT_EXTERN NSString *const UIImagePickerControllerMediaMetadata //当数据来源是相机的时候获取到的静态图像元数据，可以使用phtoho框架进行处理

C函数(保存照片或视频)
```
UIKIT_EXTERN void UIImageWriteToSavedPhotosAlbum(UIImage *image, __nullable id completionTarget, __nullable SEL completionSelector, void * __nullable contextInfo);

UIKIT_EXTERN BOOL UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(NSString *videoPath) NS_AVAILABLE_IOS(3_1);

UIKIT_EXTERN void UISaveVideoAtPathToSavedPhotosAlbum(NSString *videoPath, __nullable id completionTarget, __nullable SEL completionSelector, void * __nullable contextInfo) NS_AVAILABLE_IOS(3_1);
```
UIImageWriteToSavedPhotosAlbum用来保存照片到相册，seletor应该设置为- (void)image:(UIImage )image didFinishSavingWithError:(NSError )error contextInfo:(void )contextInfo;当照片保存到相册完成时，会调用该方法通知你。
UIVideoAtPathIsCompatibleWithSavedPhotosAlbum会返回布尔类型的值判断该路径下的视频能否保存到相册，视频需要先存储到沙盒文件再保存到相册，而照片是可以直接从代理完成的回调info字典里面获取到。
UISaveVideoAtPathToSavedPhotosAlbum用来保存视频到相册，seletor应该设置为- (void)video:(NSString )videoPath didFinishSavingWithError:(NSError )error contextInfo:(void )contextInfo;当视频保存到相册或出错时会调用该方法通知你。
这三个方法一般是在代理的完成方法didFinishPickingMediaWithInfo里面配合使用。

关于编辑照片界面的英文，可以在info.plist设置Localized resources can be mixed 的值为YES就可以转换为你当前系统的语言。更多关于info.plist的详解请参考iOS系统配置info.plist下面是关于使用UIImagePickerConreoller来上传头像,照片多选以及拍摄视频的一个Demo

iOS3