dispatch_group 日常使用
#1.常见书写方式
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_queue_create("com.formssi.get_product_detail", NULL);
dispatch_group_async(group,queue, ^{
<!--do work-->
});
dispatch_group_async(group,queue, ^{
<!--do work-->
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
<!--main thread-->
<!--do work-->
});
#2.如果做的事包含block任务，就需要给没个block任务添加入组与出组的操作
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_queue_create("com.baidu.detail", NULL);
dispatch_group_enter(group);
dispatch_group_async(group,queue, ^{
<!--do block work-->
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_group_async(group,queue, ^{
<!--do block work-->
dispatch_group_leave(group);
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
<!--main thread-->
<!--do work-->
});
#3.当我们使用其他的三方库做网络请求或则图片下载时，而请求的任务包含多个，需要 等待这些任务都执行完成之后，再返回结果，如下列子：
dispatch_group_t group = dispatch_group_create();
__block BOOL isSuccess = NO;
for (CellModel *cellModel in modelArray) {
<!--异步下载图片-->
dispatch_group_enter(group);
[[SDWebImageManager sharedManager] downloadImageWithURL:cellModel.url options:SDWebImageRetryFailed | SDWebImageLowPriority progress:nil completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
NSLog(@"downloadError = %@-%@",error,[NSThread currentThread]);
if (error) {
isSuccess = NO;
}else{
isSuccess = YES;
<!-- 获取图片大小-->
cellModel.cellHeight = WidthOfWindow * image.size.height / image.size.width;
}
dispatch_group_leave(group);
}];
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
<!-- more -->
if (isSuccess) {
completion(NetWorkingResultTypeSuccess,@"success");
}else{
completion(NetWorkingResultTypeNoData, @"error");
}
});
