尝试使用MaskedTextBox并将InsertKeyMode设置为InsertKeyMode.Overwrite。

MaskedTextBox box = ...;
box.InsertKeyMode = InsertKeyMode.Overwrite;

如果您不希望使用Masked文本框，则可以在处理KeyPress事件时执行此操作。

private void Box_KeyPress(object sender, KeyPressEventArgs e)
    {
        TextBox Box = (sender as TextBox);
        if (Box.SelectionStart < Box.TextLength && !Char.IsControl(e.KeyChar))
        {
            int CacheSelectionStart = Box.SelectionStart; //Cache SelectionStart as its reset when the Text property of the TextBox is set.
            StringBuilder sb = new StringBuilder(Box.Text); //Create a StringBuilder as Strings are immutable
            sb[Box.SelectionStart] = e.KeyChar; //Add the pressed key at the right position
            Box.Text = sb.ToString(); //SelectionStart is reset after setting the text, so restore it
            Box.SelectionStart = CacheSelectionStart + 1; //Advance to the next char
        }
    }

标准的方法是在文本框中选择现有文本，然后当用户键入时，它将自动替换现有文本

此代码似乎有一个错误。我发现你需要在Keypress事件中设置e.Handled，否则字符会被插入两次。下面是我的代码（在VB中）基于上述内容：-

Private Sub txtScreen_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtScreen.KeyPress
    If txtScreen.SelectionStart < txtScreen.TextLength AndAlso Not [Char].IsControl(e.KeyChar) Then
        Dim SaveSelectionStart As Integer = txtScreen.SelectionStart
        Dim sb As New StringBuilder(txtScreen.Text)
        sb(txtScreen.SelectionStart) = e.KeyChar
        'Add the pressed key at the right position
        txtScreen.Text = sb.ToString()
        'SelectionStart is reset after setting the text, so restore it
        'Advance to the next char
        txtScreen.SelectionStart = SaveSelectionStart + 1
        e.Handled = True
    End If
End Sub

您可以使用RichTextBox而不是TextBox。
来源：https://social.msdn.microsoft.com/Forums/en-US/966c3af9-6674-4f48-b487-7afbef05f0cb/overwrite-mode-in-a-textbox

谢谢大家！现在这是我的了参考：https://www.syncfusion.com/faq/windowsforms/textbox/how-can-i-place-a-textbox-in-overwrite-mode-instead-of-insert-mode

int surrogate = 0;
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!insertMode)
    {
        if (char.IsSurrogate(e.KeyChar))
        {
            surrogate++;
            if (surrogate % 2 != 0)
            {
                return;
            }
            surrogate = 0;
        }
        if (textBox1.Text.Length != textBox1.MaxLength && textBox1.SelectedText == ""
           && textBox1.Text != "" && textBox1.SelectionStart != textBox1.Text.Length)
        {
            textBox1.SelectionLength = 1;//對於已經輸入完成的 surrogate C#應該會正確判斷其字長度；實際測試非然也
            //for surrogate pairs input this is necessary or it will cut the pairs in wrong way above
            if (char.IsSurrogate(textBox1.SelectedText.ToCharArray()[0]))
            {
                textBox1.SelectionLength = 2;
            }
        }
    }
}

我的应用回购：https://github.com/oscarsun72/TextForCtext.git
WindowsFormsApp1/Form1.cs

不确定使用KeyPress事件是否会扰乱正常的overtype过程，或者可能是KeyPress中正在检查的特定内容，但这并不是正常的Windows文本框应该如何表现，因为当您开始键入具有高亮文本的控件时，选择应该被删除，允许您键入空的空间。当我看到If语句时，我意识到我正在寻找的行为是这样完成的：

If tb.SelectionStart < tb.TextLength AndAlso Not [Char].IsControl(e.KeyChar) Then
        tb.SelectedText = ""
    End If

我不知道为什么要保留选择，但如果需要的话，前面的代码是理想的
萨尔