实现DataGridView单元格小数输入：点自动转逗号+限制重复分隔符

需求说明 #

• 让指定DataGridView单元格支持小数输入，用户输入.作为分隔符时自动替换为,
• 限制不能输入多个分隔符（.或,），仅允许数字、单个逗号及退格键输入，直接禁止无效输入，不做事后提示

预期输入流程 #

1. 用户输入4，单元格显示4
2. 输入5，显示45
3. 输入.，自动转为,，显示45,
4. 再次输入.或,，无任何输入，仍显示45,
5. 输入6，最终显示45,6

已尝试方案 #

通过EditingControlShowing事件获取单元格的TextBox控件，绑定KeyPress和KeyDown事件尝试将.转为,并限制输入，但未达到预期效果；试过CellValidating、TextChanged等事件也未成功，不想用Double.TryParse做事后提示，希望直接拦截无效输入。

现有代码 #

Private Sub dgv_EditingControlShowing(sender As Object, e As DataGridViewEditingControlShowingEventArgs) Handles dgv.EditingControlShowing
    If TypeOf e.Control Is TextBox AndAlso dgv.CurrentCell.ColumnIndex = 3 Then
        Dim textBox As TextBox = DirectCast(e.Control, TextBox)
        AddHandler textBox.KeyPress, AddressOf DataGridViewTextBox_KeyPress
        AddHandler textBox.KeyDown, AddressOf DataGridViewCell_KeyDown
    End If
End Sub

Private Sub DataGridViewTextBox_KeyPress(sender As Object, e As KeyPressEventArgs)
    If e.KeyChar = "."c Then
        e.KeyChar = ","c
    End If
End Sub

Private Sub DataGridViewCell_KeyDown(sender As Object, e As KeyEventArgs)
    Dim nonNumberEntered As Boolean = False

    ' Checking keys to write decimal numbers: numbers, comma and delete key for corrections...
    If e.KeyCode < Keys.D0 OrElse e.KeyCode > Keys.D9 Then
        If e.KeyCode < Keys.NumPad0 OrElse e.KeyCode > Keys.NumPad9 Then
            If e.KeyCode <> Keys.Back Then
                If e.KeyCode <> Keys.Oemcomma Then
                    nonNumberEntered = True
                End If
            End If
        End If
    End If

    Dim currentTextBox As TextBox = CType(sender, TextBox)
    Dim currentText As String = currentTextBox.Text

    ' Check if the entered text matches the regular expression
    Dim inputRegex As New Regex("^[0-9]+([,][0-9]+)?$")
    Dim isValidInput As Boolean = inputRegex.IsMatch(currentText)

    If Not isValidInput Then
        nonNumberEntered = True
    End If

    If Control.ModifierKeys = Keys.Shift Then
        nonNumberEntered = True
    End If
End Sub

修正后的解决方案 #

原代码未主动抑制无效按键，也未处理文本中已存在逗号的场景，以下是调整后的代码：

1. 优化事件绑定（避免重复触发） #

每次进入编辑模式时先移除旧的事件处理器，再添加新的，防止重复绑定导致的异常：

Private Sub dgv_EditingControlShowing(sender As Object, e As DataGridViewEditingControlShowingEventArgs) Handles dgv.EditingControlShowing
    If TypeOf e.Control Is TextBox AndAlso dgv.CurrentCell.ColumnIndex = 3 Then
        Dim textBox As TextBox = DirectCast(e.Control, TextBox)
        ' 移除旧处理器
        RemoveHandler textBox.KeyPress, AddressOf DataGridViewTextBox_KeyPress
        RemoveHandler textBox.KeyDown, AddressOf DataGridViewCell_KeyDown
        ' 添加新处理器
        AddHandler textBox.KeyPress, AddressOf DataGridViewTextBox_KeyPress
        AddHandler textBox.KeyDown, AddressOf DataGridViewCell_KeyDown
    End If
End Sub

2. 完善KeyPress事件处理 #

负责字符转换和重复逗号拦截，直接禁止无效输入：

Private Sub DataGridViewTextBox_KeyPress(sender As Object, e As KeyPressEventArgs)
    Dim textBox As TextBox = DirectCast(sender, TextBox)
    
    ' 将点转换为逗号
    If e.KeyChar = "."c Then
        e.KeyChar = ","c
    End If

    ' 只允许数字、逗号、退格键
    If Not Char.IsDigit(e.KeyChar) AndAlso e.KeyChar <> ","c AndAlso e.KeyChar <> ControlChars.Back Then
        e.Handled = True
        Return
    End If

    ' 文本中已存在逗号时，禁止再次输入逗号（选中包含逗号的文本替换除外）
    If e.KeyChar = ","c AndAlso textBox.Text.Contains(",") Then
        If Not textBox.SelectedText.Contains(",") Then
            e.Handled = True
        End If
    End If
End Sub

3. 简化KeyDown事件，拦截无效组合键 #

通过SuppressKeyPress阻止无效按键生效：

Private Sub DataGridViewCell_KeyDown(sender As Object, e As KeyEventArgs)
    Dim textBox As TextBox = DirectCast(sender, TextBox)
    
    ' 禁止Shift+数字键输入符号（如!@#等）
    If e.Shift AndAlso (e.KeyCode >= Keys.D0 AndAlso e.KeyCode <= Keys.D9) Then
        e.SuppressKeyPress = True
        Return
    End If

    ' 定义允许的按键列表
    Dim allowedKeys = {Keys.D0, Keys.D1, Keys.D2, Keys.D3, Keys.D4, Keys.D5, Keys.D6, Keys.D7, Keys.D8, Keys.D9,
                       Keys.NumPad0, Keys.NumPad1, Keys.NumPad2, Keys.NumPad3, Keys.NumPad4, Keys.NumPad5, Keys.NumPad6, Keys.NumPad7, Keys.NumPad8, Keys.NumPad9,
                       Keys.Back, Keys.Oemcomma}
    
    ' 拦截不在允许列表中的按键
    If Not allowedKeys.Contains(e.KeyCode) Then
        e.SuppressKeyPress = True
    End If
End Sub

方案说明 #

• KeyPress事件处理字符级别的验证和转换，通过e.Handled = True直接禁止无效输入
• KeyDown事件拦截功能键和组合键，通过e.SuppressKeyPress = True阻止无效按键生效
• 处理了选中文本替换的场景，避免选中包含逗号的文本时无法输入新逗号的问题
• 移除重复事件绑定，防止多次触发导致的异常

内容的提问来源于stack exchange，提问作者Jaime