I found the answer for this problem. The problem is my ALAssetsLibrary I used got null by ARC. The solution is, add this static method instead of ALAssets Library..
+ (ALAssetsLibrary *)defaultAssetsLibrary {
static dispatch_once_t pred = 0;
static ALAssetsLibrary *library = nil;
dispatch_once(&pred, ^{
library = [[ALAssetsLibrary alloc] init];
});
return library;
}