Picking an Item from the Photo Library

UIImagePickerController的功能：
1.image picker功能主要有兩個：一個是捕獲picture和medias；一個是彈出一個瀏覽頁，選擇一個item

In addition to using a UIImagePickerController instance to capture new pictures and movies, you can use it to present a media browser that lets a user choose an item from their saved photo albums. The steps you take are similar to those for capturing media, as described in Taking Pictures and Movies. The differences are:

• sourceType
• take a picture or movie and save its. present a browser and display its.

Creating and Configuring a Media Browser

• 條件測試（condition test）

  • UIRequiredDeviceCapabilities info.plist

  • isSourceTypeAvailable:

• 實例化（instantiate）

  UIImagePickerController *cameraUI [[UIImagePickerController alloc] init];

• 配置（configure）

  • sourceType

    • UIImagePickerControllerSourceTypePhotoLibrary 可以訪問設(shè)備的所有相冊集，包括有攝像機的設(shè)備的相機膠卷

    • UIImagePickerControllerSourceTypeSavedPhotosAlbum 限制范圍：帶有攝像頭的設(shè)備的相機膠卷，或沒有帶有攝像頭的設(shè)備的相冊。

  • mediaType
    check which media types are available by calling the availableMediaTypesForSourceType:，給mediaType設(shè)置一個空數(shù)組會throw an exception.

  • allowsEditing
    you can custom UI, for example, specify custom cropping.

  • delegate

• 彈出（present）

  • iPhone, iPod touch full-screen present

  • iPad

    • iOS ...-9.0 UIPopoverController

    • iOS 9.0-later UIPopoverPresentationController

• 處理代理方法（conform delegate method）

  • imagePickerController:didFinishPickingMediaWithInfo: