iOS 多張圖片保存到相冊問題（add multiple images to photo album）

　　不知道朋友們有木有作過多圖保存到系統的相冊這個需求，我在用`UIImageWriteToSavedPhotosAlbum`保存圖片時候，在代理回調方`didFinishSavingWithError`中有些圖片會出現這樣的錯誤：

　　

　　

　　緣由上面寫的很清楚，在同時保存多張圖的時候，系統資源有限，來不及處理所有圖片，容易出現寫入錯誤。若是每次保存的時候一張保存完再保存另外一張，就不會出現這個錯誤了。

　　其實管理相冊的是`ALAssetsLibrary`這個類，蘋果官方對它的描述是這樣的：An instance of ALAssetsLibrary provides access to the videos and photos that are under the control of the Photos application. `ALAssetsLibrary`中提供了保存到相冊的API：

1 // With a UIImage, the API user can use -[UIImage CGImage] to get a CGImageRef, and cast -[UIImage imageOrientation] to ALAssetOrientation.
2 - (void)writeImageToSavedPhotosAlbum:(CGImageRef)imageRef orientation:(ALAssetOrientation)orientation completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock NS_DEPRECATED_IOS(4_0, 9_0, "Use creationRequestForAssetFromImage: on PHAssetChangeRequest from the Photos framework to create a new asset instead");
3 
4 // The API user will have to specify the orientation key in the metadata dictionary to preserve the orientation of the image
5 - (void)writeImageToSavedPhotosAlbum:(CGImageRef)imageRef metadata:(NSDictionary *)metadata completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock NS_DEPRECATED_IOS(4_1, 9_0, "Use creationRequestForAssetFromImage: on PHAssetChangeRequest from the Photos framework to create a new asset instead");
6 
7 // If there is a conflict between the metadata in the image data and the metadata dictionary, the image data metadata values will be overwritten
8 - (void)writeImageDataToSavedPhotosAlbum:(NSData *)imageData metadata:(NSDictionary *)metadata completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock NS_DEPRECATED_IOS(4_1, 9_0, "Use creationRequestForAssetFromImageData: on PHAssetChangeRequest from the Photos framework to create a new asset instead");

 

後面兩個須要提供圖片的metadata, 我用的是第一個方法。下面上碼~

  

1. 初始化一個全局的`ALAssetsLibrary`

 1 ALAssetsLibrary *assetsLibrary = [[ALAssetsLibrary alloc] init]; 

 

2.封裝一個方法，把須要保存的圖片放在一個數組中，每次取第一張，調用`writeImageToSavedPhotosAlbum`保存，若是保存成功，則將其移出數組，再保存下一張，若是有錯誤，我這邊是用一個bool變量`isImagesSavedFailed`來記錄（我這邊須要圖片所有保存成功）。

 1 typedef void (^completion_t)(id result);
 2 
 3 
 4 - (void) writeImages:(NSMutableArray*)images
 5           completion:(completion_t)completionHandler {
 6     if ([images count] == 0) {
 7         if (completionHandler) {
 8             // Signal completion to the call-site. Use an appropriate result,
 9             // instead of @"finished" possibly pass an array of URLs and NSErrors
10             // generated below  in "handle URL or error".
11             completionHandler(@"images are all saved.");
12         }
13         return;
14     }
15     UIImage* image = [images firstObject];
16     [assetsLibrary writeImageToSavedPhotosAlbum:image.CGImage
17                                     orientation:ALAssetOrientationUp
18                                 completionBlock:^(NSURL *assetURL, NSError *error){
19          // Caution: check the execution context - it may be any thread,
20          // possibly use dispatch_async to dispatch to the main thread or
21          // any other queue.
22          // handle URL or error
23          if (error) {
24              NSLog(@"error = %@", [error localizedDescription]);
25              isImagesSavedFailed = true;
26              return;
27          }
28          [images removeObjectAtIndex:0];
29          // next image:
30          [self writeImages:images completion:completionHandler];
31      }];
32 }

 

3. 調用示例

 1 NSMuatableArray *saveImages;//保存到相冊的圖片
 2 [self writeImages:saveImages completion:^(id result) {
 3       NSLog(@"Result: %@", result);
 4       [hud stopLoading];
 5        if (isImagesSavedFailed) {
 6             //handle failed.
 7        }else{
 8             //handle success.
 9         }
10 }];

 

參考連接 ：http://stackoverflow.com/questions/20662908/ios-programming-using-threads-to-add-multiple-images-to-library

 

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很久木有寫博客了，有不少東西木有記錄，仍是記錄下印象深一點。