要使用.DoEvents()退出while循环，需要额外单击吗? [英] An extra click required to get out of a while loop using .DoEvents() ?

问题描述

大家好，我写了一个小API gui来通过基金会现场总线进行通信.

我使用了While循环，该循环不断从总线读取一些参数值.
在While循环的结尾，我放了

Hi folks, I wrote a small API gui to communicate over foundation fieldbus.

I''ve used a While loop that constantly reads some parameter values from the bus.
At the end of the While loop, I put

Application.DoEvents()

这样我可以使用另一个按钮停止阅读过程.一切似乎都很好，也很容易..但是有一个问题:当我运行While循环并希望停止该过程时，我必须先单击表单上的任意位置，然后才能单击任何按钮(大多是停止阅读"或重置"按钮).额外的点击使我的表单显得反应迟钝和la脚.

我想知道这是否是与DoEvents()有关的问题，还是我对Foundation现场总线的使用.

任何人都经历过这种额外点击"?

so that I can use another button to stop the reading process. It all seems good and easy.. but there''s one problem: when I get the While loop running and wish to stop the process, I have to first click somewhere on the form, anywhere, before I could click any buttons(either ''stop reading'' or ''reset'' button mostly). That extra click makes my form seem unresponsive and lame.

I wonder whether this is a problem pertaining to DoEvents() or my use of Foundation fieldbus.

Anyone experience this ''extra click'' before??

推荐答案

是的，不仅限于此.切勿将DoEvents用于此类目的.对于具有自己的线性或圆形逻辑的任何事物，以及包含阻塞调用或冗长运算的任何事物，请始终使用单独的线程.即使DoEvents可以作为一种快速而又肮脏的基于UI线程的解决方法，但它并没有那么快，但对于许多情况而言却太脏而无法正常工作.

如果将非UI线程与UI应用程序一起使用，则需要了解不能直接从此类线程调用任何UI方法或属性，需要使用我在过去的回答中详细介绍的调用机制.请参阅:
Control.Invoke()与Control.BeginInvoke() [ ^ ]，
Treeview Scanner和MD5问题 [如何获取keydown事件在vb.net中的不同线程上操作 [启用禁用+多线程后控件事件不会触发 [ ^ ].

—SA

Yes, and not just this. Never use DoEvents for such purposes. Always use a separate thread for anything which has it''s own linear or circular logic, and for anything which contains blocking calls or contain lengthy operation. Even though DoEvents can work as a quick and dirty UI thread based work-around, it''s not so quick but is too dirty for many cases to work correctly.

If you use a non-UI thread with UI applications, you need to understand that you cannot call any UI methods or properties directly from such thread, you need to use invocation mechanism I describe in detail in my past answers. Please see:
Control.Invoke() vs. Control.BeginInvoke()[^],
Problem with Treeview Scanner And MD5[^].

Please also see more references on threading based on my past answers:
How to get a keydown event to operate on a different thread in vb.net[^],
Control events not firing after enable disable + multithreading[^].

—SA

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