IPhone简单的照相机和照片库

使用图像选取器和UIImagePickerController

图像选取器是通过名为UIImagePickerController的模式控制器类执行的。首先创建此类的一个实例，指定委托，并指定其图像源，然后以模式化方式启动他。图像选取器会控制iPhone让用户从已有的图像集中选择一副图片，或者使用照相机拍摄一副新图片。用户拍摄或者选择图像之后，就可以对所选图像进行一些基本的编辑，如缩放或裁剪。如果用户没有取消按钮，那么用户拍摄的或从库中选择的图像就会传到委托。

1.UIImagePickerController的静态方法:

    /*
     typedef NS_ENUM(NSInteger, UIImagePickerControllerSourceType) {
     UIImagePickerControllerSourceTypePhotoLibrary,
     UIImagePickerControllerSourceTypeCamera,
     UIImagePickerControllerSourceTypeSavedPhotosAlbum
     };
     */

   UIImagePickerControllerSourceTypePhotoLibrary表示我们想让用户使用现有照片库之外的照片。如果所指定的源当前可用，方法isSourceTypeAvailable:将返回YES。

  UIImagePickerControllerSourceTypeCamera 指定用户将使用内置的照相机拍摄图片，并将此图片返回到委托。

  UIImagePickerControllerSourceTypeSavedPhotoAlbum 指定了用户将从现有照片库中选择图像，但选择范围仅限于最近的相册。

2.在确保运行程序的设备支持要使用的图像源之后，启动图像选取器就相对容易多了：

   UIImagePickerController *picker=[[UIImagePickerController alloc] init];
   picker.delegate=self;
   picker.sourceType=UIImagePickerControllerSourceTypePhotoLibrary;
   [self presentModalViewController:picker animated:YES];
   [picker release];

在创建并配置了UIImagePickerController之后，我们使用类从UIView中继承的presentModalViewController:animated:方法，将图像选取器呈现给用户。

3.实现图像选取器控制器委托
用户退出图像选取器界面时，你希望获取的对象需要符合UIImagePickerControllerDelegate协议，此协议定义了两个方法， 

    1)imagePickerController:didFinishPickingImage:editingInfo: 第二个参数是包含用户所选照片的UIImage实例，第三个       参数是一个NSDictionary实例，如果允许编辑，并且用户裁剪或缩放了图像，那么就会传递此参数。

      此字典存储在键UIImagePickerControllerOriginalImage下未编辑的原始图像。下面给出了检索原始图像的委托方法的一个例子：

- (void)imagePickerController:(UIImagePickerController *)picker
     didFinishPickingImage:(UIImage *)image
     editingInfo:(NSDictionary *)editingInfo {
 UIImage *selectedImage=image;
 UIImage *originalImage=[editingInfo objectForKey:UIImagePickerControllerOriginalImage];

 //do something with selectedImage and originalImage

 [picker dismissModalViewControllerAnimated:YES];
}

    通过存储在键UIImagePickerControllerCropRect下的NSValue对象，editingInfo字典也可以指示在编辑期间选择了整个图像的哪一部分。也可以将此字符串转换至CGRect：

   NSValue *cropRect=[editingInfo objectForKey:UIImagePickerControllerCropRect];
   CGRect theRect=[cropRect CGRectValue];

  完成转换之后，theRect可以指明在编辑过程中所选定的原始图像的部分。如果不需要此信息，则可以忽略。

  2)imagePickerControllerDidCancel:

    在UIImagePickerControllerDelegate协议中的两种方法都标记为可选，但实际上不是，原因是：必须通过本身解除图像选取器 这样的模式视图。因此，在用户取消图像选取器时，即使不需要采取任何应用程序特定的动作，也仍然需要解除选取器。至少，imagePickerControllerDidCancel:方法要像下面这样才能保证程序正确运行：

  - (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {
 [picker dismissModalViewControllerAnimated:YES];}

4.实际测试照相机和库

创建一个CameraViewController类 在CameraViewController.h中

@interface CameraViewController : UIViewController<UIImagePickerControllerDelegate,UINavigationControllerDelegate>
{
    __weak IBOutlet UIImageView *imageView;
    
    __weak IBOutlet UIButton *takePictureButton;
    
    __weak IBOutlet UIButton *selectFromCameraRollButton;
    
}
- (IBAction)getCameraPicture:(UIButton *)sender;
- (IBAction)selectExistingPicture:(UIButton *)sender;

@end

 在CameraViewController.m中

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
    if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
        //如果用户的设备没有照相机，则隐藏Take Picture按钮和Pick from Library按钮，只允许从照片库中选择图片
        takePictureButton.hidden = YES;
        selectFromCameraRollButton.hidden = YES;
    }
    
}


- (IBAction)getCameraPicture:(UIButton *)sender {
    UIImagePickerController *picker = [[UIImagePickerController alloc]init];
    picker.delegate = self;
    picker.allowsEditing = YES;
//    picker.sourceType = (sender == takePictureButton)?UIImagePickerControllerSourceTypeCamera:UIImagePickerControllerSourceTypeSavedPhotosAlbum;
    picker.sourceType =UIImagePickerControllerSourceTypeSavedPhotosAlbum;
    [self presentViewController:picker animated:YES completion:nil];
}

- (IBAction)selectExistingPicture:(UIButton *)sender {
    if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary]) {
        UIImagePickerController *picker = [[UIImagePickerController alloc]init];
        picker.delegate = self;
        picker.allowsEditing = YES;
        picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        [self presentViewController:picker animated:YES completion:nil];
    }else{
        UIAlertView *alertView = [[UIAlertView alloc]initWithTitle:@"找不着照片" message:nil delegate:self cancelButtonTitle:@"关闭" otherButtonTitles: nil];
        [alertView show];
    }
}

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(NSDictionary *)editingInfo
{

    [self dismissModalViewControllerAnimated:YES];
}
- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker
{
   [self dismissViewControllerAnimated:YES completion:nil];
}

5.效果图