我如何使用 NSTimer（或其他）使事件在 Cocoa 中的特定时间之后发生？

Question

我正在使用 Xcode 创建一个用 Objective-C 编写的 Mac OSX Cocoa 应用程序。

这是我的代码：

-(IBAction)clickToLaunchAppButtonClicked:(id)sender; {
//I want to hide the click to load app button
[clickToLoadButton setEnabled:NO];
[clickToLoadButton setHidden:YES];

//***I want to make the app wait for 1 second (This is where I'm stuck!)***

//I want to show the loading label
[loadingLabel setEnabled:YES];
[loadingLabel setHidden:NO];

//I want to show the loading progress bar and initialize it
[loadingProgressBar setHidden:NO];
[loadingProgressBar startAnimation:self];

//***I want to make the app wait for 3 seconds (Again, I don't know how to do this!)***

//I want to stop the loading progress bar animation
[loadingProgressBar stopAnimation:self];

//I want to hide the loading progress bar and loading label
[loadingLabel setHidden:YES];
[loadingLabel setEnabled:NO];
[loadingLabel setHidden:YES];
}

如何让应用程序等待/暂停几秒钟？我尝试了 wait()、delay() 或 pause() 函数，但它们冻结了应用程序，这不是我想要的。我应该使用 NSTimer 吗？如果是这样，请给我一个简单的实现方法。

Answer 1

我建议改用新的 Grand Central Dispatch API。

例如：

-(IBAction)clickToLaunchAppButtonClicked:(id)sender {
  //I want to hide the click to load app button
  [clickToLoadButton setEnabled:NO];
  [clickToLoadButton setHidden:YES];

  // wait one second
  dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC);
  dispatch_after(popTime, dispatch_get_main_queue(), ^{

    //I want to show the loading label
    [loadingLabel setEnabled:YES];
    [loadingLabel setHidden:NO];

    //I want to show the loading progress bar and initialize it
    [loadingProgressBar setHidden:NO];
    [loadingProgressBar startAnimation:self];

    // execute the rest after 3 seconds
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 3.0 * NSEC_PER_SEC);
    dispatch_after(popTime, dispatch_get_main_queue(), ^{

      //I want to stop the loading progress bar animation
      [loadingProgressBar stopAnimation:self];

      //I want to hide the loading progress bar and loading label
      [loadingLabel setHidden:YES];
      [loadingLabel setEnabled:NO];
      [loadingLabel setHidden:YES];
    });
  });
}

有三个优点：

• 代码更少，更干净。您无需定义额外的方法，所有代码都位于一处。
• GCD api 的速度快得令人难以置信，尽管在您的示例中它可能并不重要，有时这很重要，尤其是在 iPhone 上，其中“快速”也意味着“更长的电池寿命”
• 要执行的代码与代码共享范围这就是所谓的。外部代码中的任何变量都可以在稍后执行的代码中使用

Answer 2

您可以将要在 3 秒延迟上运行的代码放在另一个方法 (delayedLoad) 中，并使用 performSelector: withObject: afterDelay:

[self performSelector:@selector(delayedLoad) withObject:nil afterDelay:3.0];

编辑 - 详细拼写以响应您的评论

以创建另一个方法，将此代码包含在同一个 .m 文件（AppDelegate.m 或类似文件）中

-(void)delayedLoad
{

//I want to stop the loading progress bar animation
[loadingProgressBar stopAnimation:self];

//I want to hide the loading progress bar and loading label
[loadingLabel setHidden:YES];
[loadingLabel setEnabled:NO];
[loadingLabel setHidden:YES];
}

，并且您现有的方法将变为

-(IBAction)clickToLaunchAppButtonClicked:(id)sender; {
//I want to hide the click to load app button
[clickToLoadButton setEnabled:NO];
[clickToLoadButton setHidden:YES];

//***I want to make the app wait for 1 second (This is where I'm stuck!)***

//I want to show the loading label
[loadingLabel setEnabled:YES];
[loadingLabel setHidden:NO];

//I want to show the loading progress bar and initialize it
[loadingProgressBar setHidden:NO];
[loadingProgressBar startAnimation:self];
[self performSelector:@selector(delayedLoad) withObject:nil afterDelay:3.0];
}

这就是您实现 3 秒延迟的方式。希望你可以扩展它以实现 1 秒延迟