不久前我遇到了同样的问题，我在Rick Brewster's blog中找到了解决方案，引用了this link。这个想法是在派生类ToolStripEx中覆盖'WndProc'。该解决方案的核心看起来像这样：

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);

    if (m.Msg == NativeConstants.WM_MOUSEACTIVATE &&
        m.Result == (IntPtr)NativeConstants.MA_ACTIVATEANDEAT)
    {
        m.Result = (IntPtr)NativeConstants.MA_ACTIVATE;
    }
}

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您可以创建自己的类，继承自ToolStrip，并使用自定义属性ClickThrough来打开或关闭行为：

Public Class ToolStripExtended : Inherits ToolStrip
    Private Const WM_MOUSEACTIVATE As UInteger = &H21
    Private Const MA_ACTIVATE As UInteger = 1
    Private Const MA_ACTIVATEANDEAT As UInteger = 2
    Private Const MA_NOACTIVATE As UInteger = 3
    Private Const MA_NOACTIVATEANDEAT As UInteger = 4

    Private _clickThrough As Boolean = False

    Public Sub New()
        MyBase.New()
    End Sub

    ''' <summary>
    ''' Gets or sets whether the ToolStripEx honours item clicks when its containing form does
    ''' not have input focus.
    ''' </summary>
    ''' <remarks>
    ''' Default value is false, which is the same behaviour provided by the base ToolStrip class.
    ''' </remarks>
    Public Property ClickThrough() As Boolean
        Get
            Return Me._clickThrough
        End Get

        Set(value As Boolean)
            Me._clickThrough = value
        End Set
    End Property

    Protected Overrides Sub WndProc(ByRef m As Message)
        MyBase.WndProc(m)

        If _clickThrough AndAlso m.Msg = WM_MOUSEACTIVATE AndAlso m.Result = New IntPtr(MA_ACTIVATEANDEAT) Then
            m.Result = New IntPtr(MA_ACTIVATE)
        End If
    End Sub
End Class

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我在其他开发环境（VB6）中遇到过这种情况，结果是因为第一次单击被工具栏吸收以获取焦点。或者，换句话说，工具栏不会响应单击 *，直到 * 它有焦点。要测试这一点，请尝试在单击按钮之前单击工具栏的空白部分。如果你从来没有点击两次按钮后，你已经点击了工具栏，那么这可能是问题。我想他们我解决了这个问题（这是几年前的事了，所以请原谅我的黑客行为）是在MouseOver事件中通过编程给予焦点放在工具栏上。

如果应用程序窗口没有获得焦点，则必须单击ToolStrip按钮两次。第一次单击将焦点设置为窗口，第二次单击将引发click事件。这是（不幸的是）默认行为，而且是有意为之。Microsoft Word显示相同的行为（即使.NET ToolStrip不是同一个控件）。

以下是@Doc Brown的解决方案的实现：

public class ToolStripX : ToolStrip
{
    private const int WM_MOUSEACTIVATE = 0x0021;
    private const int MA_ACTIVATEANDEAT = 2;
    private const int MA_ACTIVATE = 1;

    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);

        if (m.Msg == WM_MOUSEACTIVATE &&
            m.Result == (IntPtr)MA_ACTIVATEANDEAT)
        {
            m.Result = (IntPtr)MA_ACTIVATE;
        }
    }
}

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