objective c - Why does this array not being populated? -

even if assetsenumerator block executed in different thread still takes long time images fill array , that's why i'm trying this, better performance. thing i've begun scratching surface concerning multithreading , have lot of reading do. i've tried solve problem after reading few posts regarding , 1 of them being how store assets asynchronous enumerator in alassetslibrary? , in vain.

    void (^assetenumerator)(alasset *, nsuinteger, bool *) = ^(alasset *result, nsuinteger index, bool *stop)     {        if (result != null) {             dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, 0), ^{              alassetrepresentation *rep = [result defaultrepresentation];             cgimageref ref = [rep fullscreenimage];             uiimage *image = [uiimage imagewithcgimage:ref];             nslog(@"%@",image);  ->>> image exists                 dispatch_async(dispatch_get_main_queue(), ^ {                 nslog(@"%@ array",_albumpics);                [_albumpics addobject:image];             });           });       }    }; 

i tried obtain images without block classic iteration through assets array... . quick fix real great ! many

2013-04-05 16:31:42.256 photo_share[10276:907] ( ) array