剪贴板侦听器事件被调用两次 [英] clipboard Listener event is being called twice

问题描述

我想将更改保存在剪贴板中。所以我注册了我的应用程序以获取剪贴板上发生的所有更改。

i want to save the changes in my clipboard. so i registered my application to get all the changes that happens to the Clipboard.

使用

    [DllImport("User32.dll")]
    protected static extern bool AddClipboardFormatListener(int hwnd);

然后

protected override void WndProc(ref Message m)
    {
switch (m.Msg)
        {
            case WM_CLIPBOARDUPDATE:
                OnClipboardChanged();
                break;
             ...
        }
     }

private void OnClipboardChanged()
{
    if (Clipboard.ContainsText())
        {
         MessageBox.Show(Clipboard.GetText().ToString());
        }
}

问题是：
复制文本时从Visual Studio或firefox之类的应用程序中，有时会调用OnClipboardChanged（）函数两次或3次。

The Problem is: When copying text from an application like visual studio or firefox, the OnClipboardChanged() function will be called twice or 3 times sometimes.

我认为这些应用程序会将数据写入剪贴板具有不同的格式，这就是为什么多次调用该函数的原因。
但是，由于多次调用OnClipboardChanged（），我又如何防止保存相同的数据？

I think that those application will write the Data to the clipboard with different formats, this is why the function is called more than once. But how would i prevent saving the same data because OnClipboardChanged() is being called more than once ?

推荐答案

因为他们多次打开/关闭剪贴板。我以前见过如此疯狂。 Excel在复制图表时曾经执行24个单独的操作。

代替此操作（伪代码）：

Because they're opening/closing the clipboard multiple times. I've seen such madness before. Excel used to perform 24 separate operations when copying a chart.
Instead of this (pseudocode):

openClipboard
for each format {
  place data on clipboard(format)
}
closeClipboard

他们可能正在这样做：

for each format {
  openClipboard
  place data on clipboard(format)
  closeClipboard
}

更新：常用的缓解策略是避免对每个更新做出反应，并且在经过合理的稳定时间之后没有对剪贴板进行任何通知之后，对LAST更新做出反应。 500ms通常绰绰有余。

Update: The usual mitigation strategy is to avoid reacting to every update, and react to the LAST update after a reasonable "settle time" has elapsed with no further clipboard notifications. 500ms will usually be more than adequate.

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