使用Cocoa Touch如何訪問并修改用戶的照片庫

要訪問和修改用戶的照片庫，可以使用UIImagePickerController類和UIImagePickerDelegate協議。以下是一個簡單的示例代碼，演示如何訪問用戶的照片庫并顯示選定的圖片：

// 在視圖控制器中創建一個UIImagePickerController屬性
@property (nonatomic, strong) UIImagePickerController *imagePickerController;

// 實例化UIImagePickerController并設置代理
self.imagePickerController = [[UIImagePickerController alloc] init];
self.imagePickerController.delegate = self;

// 設置UIImagePickerController的sourceType為UIImagePickerControllerSourceTypePhotoLibrary，以訪問用戶的照片庫
self.imagePickerController.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;

// 顯示UIImagePickerController
[self presentViewController:self.imagePickerController animated:YES completion:nil];

// 實現UIImagePickerDelegate協議方法，處理用戶選擇的圖片
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info {
    UIImage *selectedImage = info[UIImagePickerControllerOriginalImage];
    
    // 在這里可以對選定的圖片進行處理或保存到本地
    
    // 關閉UIImagePickerController
    [picker dismissViewControllerAnimated:YES completion:nil];
}

// 實現UIImagePickerDelegate協議方法，處理用戶取消選擇
- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {
    // 關閉UIImagePickerController
    [picker dismissViewControllerAnimated:YES completion:nil];
}

這段代碼演示了如何訪問用戶的照片庫并顯示選定的圖片。您可以在didFinishPickingMediaWithInfo方法中對選定的圖片進行處理，例如顯示在UIImageView中，保存到本地等操作。在imagePickerControllerDidCancel方法中處理用戶取消選擇的情況。