如何使用ALAssetLibrary获取相机胶卷中的本地照片

Question

ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];
    [library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos
                           usingBlock:libraryGroupsEnumeration 
                         failureBlock:failureblock];
ALAssetsGroupEnumerationResultsBlock groupEnumerAtion = ^(ALAsset *result, NSUInteger index, BOOL *stop){
        if (result!=NULL) {

            if ([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto]) {

                [self._dataArray addObject:result];
            }

        }
    };

ALAssetsLibraryGroupsEnumerationResultsBlock
    libraryGroupsEnumeration = ^(ALAssetsGroup* group, BOOL* stop){
        //within the group enumeration block.filter to enumerate just photos.
        [group setAssetsFilter:[ALAssetsFilter allPhotos]];
        if (group!=nil) {
            NSString *g=[NSString stringWithFormat:@"%@",group];
            NSLog(@"gg:%@",g);//gg:ALAssetsGroup - Name:Camera Roll, Type:Saved Photos, Assets count:71
            [group enumerateAssetsUsingBlock:groupEnumerAtion];
        }
        else {
            dispatch_async(dispatch_get_global_queue(0, 0), ^{
                [self saveToDB:self._dataArray];

            });
        }

    };

假设我的相机卷有100张照片，我想在上面的代码中获得前30张照片保存到我的database.but中，我必须等待100个结果fisishing.After 30写入数据库，继续获得另外30张，直到结束。因为获取100张甚至更多的照片会延迟我的UI，所以refresh.It看起来并不舒服。非常感谢!

我该写些什么呢？

Answer 1

试试这个

if (result!=NULL) {

    if ([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto])         {

          [self._dataArray addObject:result];

            if([self._dataArray count] == 30){

               dispatch_async(dispatch_get_global_queue(0, 0), ^{

                 NSArray *array = [[NSArray alloc] initWithArray:self._dataArray]; //please change the array declaration to top of this method. Because the Block will not allow to do it here.               
                 [self._dataArray removeAllObjects];
                 [self saveToDB:array];
                 //array release,if not using ARC

           });
       }
    }

}

和

if (group!=nil) {

            [group enumerateAssetsUsingBlock:groupEnumerAtion];
        }
        else if([self._dataArray count] > 0) {

              dispatch_async(dispatch_get_global_queue(0, 0), ^{

                    [self saveToDB:self._dataArray];

            });
        } 

Answer 2

您应该尝试保存到后台线程上的数据库，并让CoreData (假设您使用CoreData)通过处理NSManagedObjectContextDidSaveNotification来更新主线程上的NSManagedObjectContext。

你仍然可以在30张照片后保存，这可能会减轻一些I/O压力，但你必须测试性能。