VB.Net文本框MaxLength

Question

Private Sub txtCaptcha_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtCaptcha.KeyPress
    If Char.IsLower(e.KeyChar) Or Char.IsNumber(e.KeyChar) Then
        Dim pos As Integer = txtCaptcha.SelectionStart
        txtCaptcha.Text = txtCaptcha.Text & Char.ToUpper(e.KeyChar)
        txtCaptcha.SelectionStart = pos + 1
        e.Handled = True
    End If
End Sub

我在文本框maxlength中使用此事件后不起作用

如何使此代碼具有maxlength 6個字符？

Answer 1

顯然，MaxLength僅適用於用戶輸入。 這是有道理的，因為您的文本框可以從綁定的數據源中獲取數據，並且您將截斷現有數據。

如果你這樣做

textBox1.Text = "something" 

通過代碼仍然允許。

我建議您將常規更改為

    If txtCaptcha.Text.Length < txtCaptcha.MaxLength AndAlso (Char.IsLower(e.KeyChar) Or Char.IsNumber(e.KeyChar)) Then
        Dim pos As Integer = txtCaptcha.SelectionStart
        txtCaptcha.Text = txtCaptcha.Text & Char.ToUpper(e.KeyChar)
        txtCaptcha.SelectionStart = pos + 1
        e.Handled = True
    End If

如果達到MaxLength，則不會處理輸入，但是控件將攔截輸入並提供錯誤聲音，就像每個設置了MaxLength的TextBox一樣。

Answer 2

這樣嘗試

Private Sub txtCaptcha_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtCaptcha.KeyPress
    If txtCaptcha.MaLength = txtCaptcha.Text.Length Then
        e.Handled = true
        Exit Sub
    End If

    'For Ctrl+V
    If AscW(e.KeyChar) = 22 Then
        Dim strPaste As String = My.Computer.Clipboard.GetText() & txtCaptcha.Text
        If strPaste.Length > txtCaptcha.MaLength Then
            strPaste = strPaste.Substring(0, txtCaptcha.MaLength)
            txtCaptcha.Text = strPaste
            e.Handled = True
            Exit Sub
        End If
    End If

    If Char.IsLower(e.KeyChar) Or Char.IsNumber(e.KeyChar) Then
        Dim pos As Integer = txtCaptcha.SelectionStart
        txtCaptcha.Text = txtCaptcha.Text & Char.ToUpper(e.KeyChar)
        txtCaptcha.SelectionStart = pos + 1
        e.Handled = True
    End If
End Sub

Answer 3

您可以在form load初始化控件和變量，然后在form_load中為文本框設置MaxLength的代碼，如下所示

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    txtCaptcha.MaxLength = 6
End Sub