ios - 如何在 Swift 中枚举 ALAssetsGroup

Question

我尽力了，但我被困在这里。我想导入 iPhone 相册中的所有照片。所以我想出了这个 ALAssestsLibrary API。

 photoLibrary.enumerateGroupsWithTypes(ALAssetsGroupType(ALAssetsGroupSavedPhotos), usingBlock: { group  in
        if group != nil

        {

        }

        }, failureBlock: { error in println("\(error)")})

如何添加这行代码。

group enumerateAssetsUsingBlock:groupEnumerAtion

我尝试添加它，但它没有显示任何 enumerateAssetsUsingBlock 属性。？

这是实际的代码。 !!在 Objective-C 中

    dispatch_async(dispatch_get_main_queue(), ^
        {
            @autoreleasepool
            {
                ALAssetsLibraryAccessFailureBlock failureblock = ^(NSError *myerror)
                    {
                        NSLog(@"error occour =%@", [myerror localizedDescription]);
                };

                ALAssetsGroupEnumerationResultsBlock groupEnumerAtion = ^(ALAsset *result, NSUInteger index, BOOL *stop)
                    {
                        if (result!=NULL)
                        {
                            if ([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto])
                            {
                                [self.g_imageArray addObject:result];
                            }
                        }
                };

                ALAssetsLibraryGroupsEnumerationResultsBlock
                libraryGroupsEnumeration = ^(ALAssetsGroup* group, BOOL* stop)
                    {
                        if (group == nil)
                        {
                            return;
                        }

                        if (group!=nil) {
                            [group enumerateAssetsUsingBlock:groupEnumerAtion];
                        }
                        [self updatephotoList];
                };

                self.library = [[ALAssetsLibrary alloc] init];
                [self.library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos
                usingBlock:libraryGroupsEnumeration 
                failureBlock:failureblock];
            }
        });

Answer 1

你的 enumerationBlock和 failureBlock没有正确的类型。比如枚举 block 定义为

typealias ALAssetsLibraryGroupsEnumerationResultsBlock = (ALAssetsGroup!, UnsafeMutablePointer<ObjCBool>) -> Void

这意味着参数是一个采用 (ALAssetsGroup!, UnsafeMutablePointer<ObjCBool>) 的闭包作为参数并返回 Void :

{
     (group: ALAssetsGroup!, stop: UnsafeMutablePointer<ObjCBool>) -> Void in
     // ...
}

所以你的代码应该是这样的:

photoLibrary.enumerateGroupsWithTypes(ALAssetsGroupType(ALAssetsGroupSavedPhotos),
    usingBlock: {
        (group: ALAssetsGroup!, stop: UnsafeMutablePointer<ObjCBool>) -> Void in
        if group != nil {
            group.enumerateAssetsUsingBlock({
                (asset: ALAsset!, index: Int, stop: UnsafeMutablePointer<ObjCBool>) -> Void in
                    // ...
                })
        }
    },
    failureBlock: {
        (myerror: NSError!) -> Void in
        println("error occurred: \(myerror.localizedDescription)")
    })

由于 Swift 的“自动类型推断”特性，你也可以这样写作为

photoLibrary.enumerateGroupsWithTypes(ALAssetsGroupType(ALAssetsGroupSavedPhotos),
    usingBlock: {
        group, stop in
        if group != nil {
            group.enumerateAssetsUsingBlock({
                asset, index, stop in
                // ...
                })
        }
    },
    failureBlock: {
        myerror in
        println("error occurred: \(myerror.localizedDescription)")
    })

但在这种情况下，第一个版本可能更容易理解。