问题描述
我已经看到了对 GUI 控件进行跨线程访问的常见设置，如下所述:最短的写法对 Windows 窗体控件的线程安全访问方法
I've seen the common setup for cross threading access to a GUI control, such as discussed here: Shortest way to write a thread-safe access method to a windows forms control
我发现的所有网络点击都描述了类似的事情.
All the web hits I found describe a similar thing.
但是，为什么我们需要检查 InvokeRequired?我们不能直接调用 Invoke 吗?
However, why do we need to check InvokeRequired? Can't we just call Invoke directly?
我假设答案是否定的，所以我真正的问题是为什么"?
I assume the answer is no, so my real question is 'why'?
推荐答案
从非 UI 线程我们无法触摸 UI - 可能会发生非常糟糕的事情，因为控件具有线程关联性.因此，我们必须(至少)从非 UI 线程调用 Invoke 或 BeginInvoke.
From non-UI threads we can't touch the UI - very bad things can happen, since controls have thread affinity. So from a non-UI thread we must (at a minumum) call Invoke or BeginInvoke.
然而，对于 UI 线程 - 我们不想要调用 Invoke 很多时间；问题是，如果您已经在 UI 线程上，它仍然有向表单的泵发送消息并进行处理的不必要开销.
For UI-threads, however - we don't want to call Invoke lots of time; the issue is that if you are already on the UI thread, it still has the unnecessary overhead of sending a message to the form's pump and processing it.
实际上，在您知道的大多数线程代码中，您希望在 非-UI 线程上调用特定方法，因此在这些情况下，不需要额外的开销:只需调用 Invoke.
In reality, in most threading code you know you expect a specific method to be called on a non-UI thread, so in those cases, there is no additional overhead: just call Invoke.
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