Question

我有一个UITableViewController，它是RootViewController。它的XIB只有一个表格视图。我通过IB添加了一个UIActivityIndicator并创建了一个IBOutlet。我已经以编程方式向RootViewController添加了一个带有删除按钮的工具栏。当用户单击工具栏的删除按钮时，我想以屏幕为中心显示指示符。下面的方法从数据库中删除数据，这种情况发生得非常快。我想让用户知道正在发生的事情。如果我在没有sleep（）的情况下运行下面的代码，它会快速发生并且我看不到指示器。但有些人出于某种原因，我还是没有看到这个指标。我猜睡眠（）块重新粉刷？如果我拿出睡眠（）和最后两行，我会看到指示器但当然它永远不会消失。它也显示在窗口的左上角。

如何让下面的代码工作，使指示器至少显示1/2 - 1秒？

如何将指示器对准窗口中间？

[self.navigationController.view addSubview:activityIndicator];
[activityIndicator startAnimating];
[activityIndicator setNeedsDisplay];

//do something which might happen really fast

sleep(1); //create illusion
[activityIndicator stopAnimating];
[activityIndicator removeFromSuperview];

Answer 1

在您处理完事件并返回到运行循环之前，微调器不会开始旋转。解决这个问题的方法是让运行循环为你完成任务。

这是我的意思的一个例子：

- (IBAction)deleteAction:(id)sender {
    [self.navigationController.view addSubview:activityIndicator];
    [activityIndicator startAnimating];

    // Spinner won't start spinning until we finish processing this event, so
    // we're just going to schedule the rest of what we need to do.

    // doDelete: will run when the main thread gets its next event.
    [self performSelectorOnMainThread:@selector(doDelete:)
                           withObject:record
                        waitUntilDone:NO];

    // removeSpinner: will run in at least one second, but will wait if
    // another event (like the doDelete: one) is in the middle of running.
    [self performSelector:@selector(removeSpinner:)
               withObject:activityIndicator
               afterDelay:1.0];
}
- (void)doDelete:(id)record {
    [record delete];   // or whatever it is you need to do
}
- (void)removeSpinner:(UIActivityIndicator*)activityIndicator {
    [activityIndicator stopAnimating];
    [activityIndicator removeFromSuperview];
}

注意：此代码中没有任何内容可以保证在“休眠”期间阻止其处理其他触摸，因此请确保以某种方式锁定其他事件。

Answer 2

正如Adam所提到的，除非工作（在本例中为Delete操作）在后台线程中完成，否则微调器不会显示。这是我根据布伦特的初始代码开始工作的代码。我修改它来调用我在后台线程中完成工作的函数，然后在完成后使用主线程删除微调器。

- (void)removeSpinner:(id)record {
    [activityIndicator stopAnimating];
    [activityIndicator removeFromSuperview];

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Thank You" message:@"Thanks for your feedback!"
                                                                                                 delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
    [alert release];

    // return to feedings tab
  tabBarController.selectedIndex = 0;
}


- (void)doFeedback:(id)record {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    int j;
    for (int i = 0; i < 1000000000; i++) {
        j = j + i;
    }
    [self performSelectorOnMainThread:@selector(removeSpinner:) withObject:nil waitUntilDone:NO];

    [pool release];
}


- (IBAction)handleSend {        
    [self.view addSubview:activityIndicator];
    [activityIndicator startAnimating];

    // Spinner won't start spinning until we finish processing this event, so
    // we're just going to schedule the rest of what we need to do. 
    // doFeedback: will run when the main thread gets its next event.   
    [self performSelectorInBackground:@selector(doFeedback:) withObject:nil];
}

Answer 3

问题在于，当你正在做你的事情时，主运行循环没有运行。为了显示活动指示器，需要运行主运行循环，以便更新其动画。为了获得预期的行为，您需要在一个单独的线程中异步执行数据库操作。

Answer 4

[self.navigationController.view addSubview：activityIndicator]; [activityIndicator startAnimating];

[self performSelector：@selector（removeSpinner :) withObject：activityIndicator afterDelay：5.0];

显示UIActivityIndicator持续x秒

4 个答案:

显示UIActivityIndi​​cator持续x秒

4 个答案:

显示UIActivityIndicator持续x秒