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问题：如何提高判断力 如何判断一个异步操作循环完全结束了呢？
描述:
解决方案1:
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) {
}];
}解决方案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 ui
NSLog(@"%@", 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);
}];