PhotosFramework 将资产分配给相册

Posted 2023-03-08

【中文标题】PhotosFramework 将资产分配给相册

【英文标题】：PhotosFramework assign asset to album

【发布时间】：2016-08-07 02:24:20

【问题描述】：

我查看了几个示例，但无法弄清楚这一点。我觉得我在这里遗漏了一些简单的东西。

在我的应用程序中，我想在特定相册 (ABC) 中拍摄一张图像，并将其添加到我专门为此应用程序创建的另一个相册 (XYZ) 中。这两个相册都将在 ios 的默认照片应用中可见。

如果我保存图像的另一个副本，我可以成功地将图像分配给专辑 XYZ。即，如果我现在回到相机胶卷，我将看到同一图像的两个副本。一张分配给专辑 ABC，另一张分配给 XYZ。这不是我想要的。我有数千张图片将分配给专辑 XYZ，我不希望两个副本不必要地占用空间。

这是我将图像副本保存到新相册的代码：

-(void) saveImage:(UIImage*) imageToSave toCollection:(NSString *) collectionTitle forRowNumber:(long) rowNumber

    NSLog(@"entered %s", __PRETTY_FUNCTION__);
    __block PHFetchResult *photosAsset;
    __block PHAssetCollection *collection;
    __block PHObjectPlaceholder *placeholder;

        // Find the album
    PHFetchOptions *fetchOptions = [[PHFetchOptions alloc] init];

    fetchOptions.predicate = [NSPredicate predicateWithFormat:@"title = %@", collectionTitle];
                // this is how we get a match for album Title held by 'collectionTitle'

    collection = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAny options:fetchOptions].firstObject;

        // check if album exists
    if (!collection)
    
        [[phphotoLibrary sharedPhotoLibrary] performChanges:^

            NSLog(@" Album did not exist, now creating album: %@",collectionTitle);
                // Create the album
            PHAssetCollectionChangeRequest *createAlbum = [PHAssetCollectionChangeRequest creationRequestForAssetCollectionWithTitle:collectionTitle];

            placeholder = [createAlbum placeholderForCreatedAssetCollection];

         completionHandler:^(BOOL didItSucceed, NSError *error) 
            if (didItSucceed)
            
                PHFetchResult *collectionFetchResult = [PHAssetCollection fetchAssetCollectionsWithLocalIdentifiers:@[placeholder.localIdentifier] options:nil];

                collection = collectionFetchResult.firstObject;
            
        ];
    

        // Save to the album
    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^

        PHAssetChangeRequest *assetRequest = [PHAssetChangeRequest creationRequestForAssetFromImage:imageToSave];

        placeholder = [assetRequest placeholderForCreatedAsset];
        photosAsset = [PHAsset fetchAssetsInAssetCollection:collection options:nil];

        PHAssetCollectionChangeRequest *albumChangeRequest = [PHAssetCollectionChangeRequest changeRequestForAssetCollection:collection assets:photosAsset];

        [albumChangeRequest addAssets:@[placeholder]];

     completionHandler:^(BOOL didItSucceed, NSError *error) 

        if (didItSucceed)
               // if YES


            NSLog(@" Looks like Image was saved in camera Roll as %@", placeholder.localIdentifier);
            NSLog(@"placeholder holds %@", placeholder.debugDescription );

        
        else
        
            NSLog(@"%@", error);
        

    ];

我知道使用 IOS 照片应用程序可以将图像分配给多个相册，并且不会创建多个副本。

【参考方案1】：

您正在将新图像添加到库中，因为您明确请求将新图像添加到库中：

PHAssetChangeRequest *assetRequest = [PHAssetChangeRequest creationRequestForAssetFromImage:imageToSave];

如果您有一个代表原始图像的PHAsset，您可以请求将相同的资产添加到您的第二个相册。但是由于您共享的代码以 UIImage 开头，因此您失去了与原始资产的连接。

假设您在某处拥有 PHAsset，您需要的内容如下所示：

- (void)saveAsset:(PHAsset *)asset toCollectionNamed:(NSString *) collectionTitle 

    // Find the album
    PHFetchOptions *fetchOptions = [[PHFetchOptions alloc] init];
    fetchOptions.predicate = [NSPredicate predicateWithFormat:@"title = %@", collectionTitle];
    PHAssetCollection *collection = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAny options:fetchOptions].firstObject;

    // Combine (possible) album creation and adding in one change block
    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^
        PHAssetCollectionChangeRequest *albumRequest;
        if (collection == nil) 
            // create the album if it doesn't exist
            albumRequest = [PHAssetCollectionChangeRequest creationRequestForAssetCollectionWithTitle:collectionTitle];
         else 
            // otherwise request to change the existing album
            albumRequest = [PHAssetCollectionChangeRequest changeRequestForAssetCollection:collection];
        
        // add the asset to the album
        [albumRequest addAssets:@[asset]];

     completionHandler:^(BOOL success, NSError *error) 
        if (!success) 
            NSLog(@"error creating or adding to album: %@", error);
        
    ];

请注意，您不需要两个 PHPhotoLibrary performChanges 块 — 您可以创建相册并将其添加到同一个更改请求中。

【讨论】：

完美，谢谢！！这完全符合我的需要。使用相同的执行更改请求的额外好处。