Csharp 在选项卡之间切换时，如何将焦点恢复到以前聚焦的 TabPage 控件

可能的解决方案:

Override UpdateDefaultButton() in your Form; this method is called each time a Control becomes the ActiveControl.
Of course, if you have UserControls inside TabPages, the ActiveControl is the UserControl, but you need its child Control that is currently focused.

在示例代码中，我使用GetFocus()函数获取聚焦控件的句柄，然后使用Control.FromHandle()获取带有该句柄的控件实例，如果不是null，则将该信息与当前选项卡页一起存储在字典中.

When the TabControl's Selected event is raised, check whether the Dictionary has stored the new current TabPage and, if a Control is associated with that TabPage, move the focus on it.
(I'm using BeginInvoke() because we're changing the ActiveControl in the Selected handler, which would in turn cause a call to UpdateDefaultButton())

• 注意，这里我并不是在验证聚焦控件是否是TabPage之外的其他容器的子容器:如果TabPage中有嵌套的容器，则需要一个递归方法来判断祖先之一是否是TabPage.

Private tabPagesActiveControl As New Dictionary(Of Integer, Control)

Protected Overrides Sub UpdateDefaultButton()
    MyBase.UpdateDefaultButton()
    If ActiveControl Is Nothing Then Return

    If TypeOf ActiveControl.Parent Is TabPage Then
        Dim tp = DirectCast(ActiveControl.Parent, TabPage)
        Dim tabPageIdx = DirectCast(tp.Parent, TabControl).SelectedIndex
        Dim ctl = FromHandle(GetFocus())

        If ctl IsNot Nothing Then
            If tabPagesActiveControl.Count > 0 AndAlso tabPagesActiveControl.ContainsKey(tabPageIdx) Then
                tabPagesActiveControl(tabPageIdx) = ctl
            Else
                tabPagesActiveControl.Add(tabPageIdx, ctl)
            End If
        End If
    End If
End Sub

Private Sub TabControl1_Selected(sender As Object, e As TabControlEventArgs) Handles TabControl1.Selected
    Dim ctl As Control = Nothing
    If tabPagesActiveControl.TryGetValue(e.TabPageIndex, ctl) Then
        BeginInvoke(New Action(Sub() ctl.Focus()))
    End If
End Sub

Win32函数声明:

<DllImport("user32.dll", CharSet:=CharSet.Auto)>
Friend Shared Function GetFocus() As IntPtr
End Function

C# Version:

private Dictionary<int, Control> tabPagesActiveControl = new Dictionary<int, Control>();

protected override void UpdateDefaultButton()
{
    base.UpdateDefaultButton();
    if (ActiveControl is null) return;

    if (ActiveControl.Parent is TabPage tp) {
        var tabPageIdx = (tp.Parent as TabControl).SelectedIndex;
        var ctl = FromHandle(GetFocus());
        if (ctl != null) {
            if (tabPagesActiveControl.Count > 0 && tabPagesActiveControl.ContainsKey(tabPageIdx)) {
                tabPagesActiveControl[tabPageIdx] = ctl;
            }
            else {
                tabPagesActiveControl.Add(tabPageIdx, ctl);
            }
        }
    }
}

private void tabControl1_Selected(object sender, TabControlEventArgs e)
{
    if (tabPagesActiveControl.TryGetValue(e.TabPageIndex, out Control ctl)) {
        BeginInvoke(new Action(() => ctl.Focus()));
    }
}

Win32函数声明:

[DllImport("user32.dll", CharSet = CharSet.Auto)]
internal static extern IntPtr GetFocus();

This is how it works:
Note: TabPage2 and TabPage3 contain the instance of a UserControl with 2 TextBoxes and a ListBox. TabPage1 contains a TextBox and a NumericUpDown.