问题描述
需求 : 获取相册信息后获取第一张图片并为self.editImageView赋值显示.问题 : 但是我现在想在getImageForCollectionView完全结束后来为self.editImageView赋值,那么问题来了,我如何才能判断getImageForCollectionView函数已经进行完毕？
- (void)getImageForCollectionView{ _library = [[ALAssetsLibrary alloc] init]; self.photos = [NSMutableDictionary dictionary]; [_library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {if (group) { NSMutableArray *array = [NSMutableArray array]; [group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {if (result) { [array addObject:result];} }]; [self.photos setValue:array forKey:[group valueForProperty:@'ALAssetsGroupPropertyName']];} } failureBlock:^(NSError *error) { }];}
问题解答
回答1：将耗时的操作放在非主线程中，需要UI更新的放在主线程中。
__weak typeof(self) weakSelf = self;dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ // not in main block task [weakSelf getImageForCollectionView]; dispatch_async(dispatch_get_main_queue(), ^{// main block. change uiNSLog(@'%@', weakSelf.photos); });});
EDIT:
- (void)getImageForCollectionView:(void(^)(void))callback { _library = [[ALAssetsLibrary alloc] init]; self.photos = [NSMutableDictionary dictionary];dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{[_library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) { if (group) {NSMutableArray *array = [NSMutableArray array];[group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) { if (result) {[array addObject:result]; }}];[self.photos setValue:array forKey:[group valueForProperty:@'ALAssetsGroupPropertyName']]; }} failureBlock:^(NSError *error) { }];dispatch_async(dispatch_get_main_queue(), ^{ callback();}); });}
[self getImageForCollectionView:^{ // ... NSLog(@'%@', self.photos);}];
