Question

我想在开始长任务之前显示进度HUD，并在任务完成后将其关闭。现在UI冻结了一段时间，然后HUD显示一秒钟然后消失。再过4-5秒后，任务结束并显示结果，但进度HUD已经消失。

- (void) addProcess:(NSString *)searchTerm
{
    dispatch_sync(dispatch_get_main_queue(), ^{
        UIApplication *app = [UIApplication sharedApplication];
        app.networkActivityIndicatorVisible = YES;
        [SVProgressHUD showWithMaskType:SVProgressHUDMaskTypeGradient];
    });

    //DO SOME VERY LONG STUFF HERE

    dispatch_sync(dispatch_get_main_queue(), ^{
        UIApplication *app = [UIApplication sharedApplication];
        app.networkActivityIndicatorVisible = NO;
        [SVProgressHUD dismiss];
    });
}

我使用SVProgressHUD进行HUD进度。我使用addProcess

调用方法dispatch_async()

如果我使用旧版+[NSThread detach...]，它可以完美运行，但我不想再使用它了。

Answer 1

有几件事：

关键观察是始终使用dispatch_async，除非您需要dispatch_sync。您不需要在此处进行同步操作，因此只需使用dispatch_async进行UI更新。
如果您从主队列运行addProcess，则无需将第一个UI更新分发回主队列。显然，如果你是从后台队列中运行它，那么你就可以了。
最初的问题是在addProcess内调度到后台队列，这对我来说更有意义（保持所有GCD内容很好地封装）。你已经更新了你的答案，说你是通过dispatch_async([self addProcess])来调用它的（我假设你的意思是全局队列，而不是主队列），我不那么疯狂了。我在下面的代码示例中解决了这两种情况。

所以，简而言之，如果你通过[self addProcess]调用它（没有将它本身发送到后台队列），我建议：

- (void) addProcess:(NSString *)searchTerm
{
    UIApplication *app = [UIApplication sharedApplication];
    app.networkActivityIndicatorVisible = YES;
    [SVProgressHUD showWithMaskType:SVProgressHUDMaskTypeGradient];

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        //DO SOME VERY LONG STUFF HERE

        dispatch_async(dispatch_get_main_queue(), ^{
            UIApplication *app = [UIApplication sharedApplication];
            app.networkActivityIndicatorVisible = NO;
            [SVProgressHUD dismiss];
        });
    });
}

或者，或者，

- (void) addProcess:(NSString *)searchTerm
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        dispatch_async(dispatch_get_main_queue(), ^{
            UIApplication *app = [UIApplication sharedApplication];
            app.networkActivityIndicatorVisible = YES;
            [SVProgressHUD showWithMaskType:SVProgressHUDMaskTypeGradient];
        });

        //DO SOME VERY LONG STUFF HERE

        dispatch_async(dispatch_get_main_queue(), ^{
            UIApplication *app = [UIApplication sharedApplication];
            app.networkActivityIndicatorVisible = NO;
            [SVProgressHUD dismiss];
        });
    });
}

如果你正在......

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [self addProcess]; 
});

那就是：

- (void) addProcess:(NSString *)searchTerm
{
    dispatch_async(dispatch_get_main_queue(), ^{
        UIApplication *app = [UIApplication sharedApplication];
        app.networkActivityIndicatorVisible = YES;
        [SVProgressHUD showWithMaskType:SVProgressHUDMaskTypeGradient];
    });

    //DO SOME VERY LONG STUFF HERE

    dispatch_async(dispatch_get_main_queue(), ^{
        UIApplication *app = [UIApplication sharedApplication];
        app.networkActivityIndicatorVisible = NO;
        [SVProgressHUD dismiss];
    });
}

在主调度队列上显示UI元素会导致元素出现然后消失

1 个答案: