perfomSelector: withObject: afterDelay: 我可以要求低优先级吗？
发送此消息时是否有某种方法可以指定我宁愿在所有待处理的 UI 事件（如果有）之后执行选择器？ IE。 在事件队列中给我的 aterDelay 计时器一个较低的优先级。
Is there some way when sending this message to specify that I rather have my selector performed after all pending UI events, if any? Ie. give my aterDelay timer a lower priority in the event queue.
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实际上，performSelector:withObject:afterDelay: 不一定必须发生在主线程上； 这就是为什么有一个单独的方法
performSelectorOnMainThread:withObject:waitUntilDone:。performSelector:withObject:afterDelay:的文档说如果您想在后台执行任务，您可以查看 +[NSThread detachNewThreadSelector:toTarget:withObject:]，它将启动一个新线程来执行您的任务，并使 UI 保持响应。 使用单独的线程来执行长时间运行的任务通常是一个好主意，否则可能会锁定您的 UI，但它确实会增加复杂性。 如果您不熟悉线程，您最终可能会遇到没有任何意义的错误。
在上面的评论中，您提到您认为动画可能导致您的 UI 无响应。 如果您使用内置的动画支持（Core Animation 或 Cocoa 包装器之一），动画不应导致您的 UI 无响应。 UI 无响应通常意味着您的程序在让运行循环返回服务 UI 事件之前正在主线程上执行大量工作。
Actually,
performSelector:withObject:afterDelay:doesn't necessarily have to occur on the main thread; that's why there's a separate methodperformSelectorOnMainThread:withObject:waitUntilDone:. The documentation forperformSelector:withObject:afterDelay:saysIf you want to perform a task in the background, you might look into
+[NSThread detachNewThreadSelector:toTarget:withObject:], which will launch a new thread to perform your task, and leave the UI responsive. Using a separate thread to execute a long-running task which might otherwise lock up your UI is generally a good idea, but it does add complexity. If you're not familiar with threading, you may end up with bugs that won't make any sense.In a comment above, you mentioned that you think animation may be at fault for making your UI unresponsive. If you're using the built-in support for animation (Core Animation or one of the Cocoa wrappers), animation shouldn't make your UI unresponsive. An unresponsive UI generally means that your program is doing a lot of work on the main thread before letting the run loop get back to service UI events.
不直接。 如果您使用
performSelector:withObject:afterDelay:，选择器将在主线程上执行，因此根据定义，它将在执行所有当前“待处理”UI 事件之后发生 -但这可能是在滚动或动画的中间，您可能会认为这是一个连续事件，但实际上是数百个单独的事件。但是，您可以使用
performSelectorInBackground:withObject:实现类似的效果，然后在被调用的方法中调用[NSThread setThreadPriority:0.01]。 请小心 — 您正在打开一个后台线程，因此您无法执行任何 UI 调用。 但是，这将允许您在优先级低于主 UI 线程的后台线程上执行工作。 （记住要设置一个自动释放池，因为它在自己的线程中！）Not directly. If you use
performSelector:withObject:afterDelay:the selector is performed on the main thread, so by definition it will occur after all current "pending" UI events have been performed—but this might be in the middle of a scroll or animation, which you would probably consider to be one continuous event but is actually hundreds of separate ones.However, you can achieve something similar using
performSelectorInBackground:withObject:, and then calling[NSThread setThreadPriority:0.01]in the method being called. Be careful—you're opening a background thread, so you can't do any UI calls. However, this will allow you to do the work on a background thread with lower priority than the main UI thread. (Remember to set up an autorelease pool since it's in its own thread!)