关于e.cancel

Question

你好！
     在Validating事件的处理函数中，如果验证失败，就将CancelEventArgs 类型的参数e的 Cancel 属性设置为 true ，则正常情况下将在 Validating 事件之后发生的所有事件均被取消。当然，你添加按钮的事件也取消了，例如这样：
         private void textBox1_Validating(object sender, CancelEventArgs e)
        {
            if (this.textBox1.Text == "aaa")
                e.Cancel = true;
        }
      希望以上解释对你有一些帮助，如果还有疑问，我们可以继续讨论啊！

---

周雪峰

按照上面的建议，运行改后的代码，仍然是在报错的同时，执行click事件，成功插入带有错误的信息，这是怎么回事？
程序执行顺序：1）先将两个文本框输入值，不分先后。2）点击按钮，执行click  事件。
麻烦帮忙看看，实在不知道是哪里的问题？
谢谢！
我改后的代码为： Private Sub TextBox1_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
        If Not Regex.IsMatch(TextBox1.Text, "^\s*\d{2}\s*$") Then
            ErrorProvider1.SetError(TextBox1, "图书类型编号应由2位数字组成！")
            TextBox1.Focus()
            Return
        Else
            ErrorProvider1.SetError(TextBox1, "")
        End If

        con.Open()
        Dim cmd1 As New SqlCommand("select * from try where typeno='" & Me.TextBox1.Text.Trim() & "'", con)
        Dim reader As SqlDataReader
        reader = cmd1.ExecuteReader()
        If (reader.Read()) Then
            ErrorProvider1.SetError(TextBox1, "此编号已存在，请重新输入！")
            TextBox1.Focus()

            e.Cancel = True

        Else
            ErrorProvider1.SetError(TextBox1, "")
        End If
        con.Close()
    End Sub

    Private Sub TextBox2_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs)
        If Not Regex.IsMatch(TextBox2.Text, "^[a-w]{2}") Then
            ErrorProvider1.SetError(TextBox2, "图书类型名称应由小写字母组成！")
            TextBox2.Focus()
            Return
        Else
            ErrorProvider1.SetError(TextBox2, "")
        End If

        con.Open()
        Dim cmd1 As New SqlCommand("select * from try where bname='" & Me.TextBox2.Text.Trim() & "'", con)
        Dim reader As SqlDataReader
        reader = cmd1.ExecuteReader()
        If (reader.Read()) Then
            ErrorProvider1.SetError(TextBox2, "此编号已存在，请重新输入！")
            TextBox2.Focus()
            e.Cancel = True
        Else
            ErrorProvider1.SetError(TextBox2, "")
            'f2 = True
        End If
        con.Close()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        con.Open()
        Dim cmd1 As New SqlCommand("insert into try values('" & TextBox1.Text & "','" & TextBox2.Text & "')", con)
        cmd1.ExecuteNonQuery()
        MsgBox("添加操作成功！", 64, "提示")
        con.Close()
        TextBox1.Text = ""
        TextBox2.Text = ""
    End Sub

Answer 1

不应该啊！我测试过，如果出错，Click事件处理函数是不会执行的！
你这里好象有问题：
        If Not Regex.IsMatch(TextBox2.Text, "^[a-w]{2}") Then
            ErrorProvider1.SetError(TextBox2, "图书类型名称应由小写字母组成！")
            TextBox2.Focus()
            Return
        Else
如果出错，直接返回了，也没有设置e.Cancel=true啊！

---

周雪峰

Answer 2

程序启动后，我的操作步骤是：先在textbox1里输入,程序判断合法后，再在textbox2里输入,然后点击“添加”按钮，程序提示“插入成功！”
我在单步执行时发现：程序对textbox1进行判断，输入合法后，会直接跳到 按钮的click事件，根本没执行textbox2的验证事件，这是为什么？再麻烦你给看看。
代码：
Private Sub TextBox1_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
        If Not Regex.IsMatch(TextBox1.Text, "^\s*\d{2}\s*$") Then
            ErrorProvider1.SetError(TextBox1, "图书类型编号应由2位数字组成！")
            TextBox1.Focus()

            e.Cancel = True

            Return
        Else
            ErrorProvider1.SetError(TextBox1, "")
        End If
        con.Open()
        Dim cmd1 As New SqlCommand("select * from try where typeno='" & Me.TextBox1.Text.Trim() & "'", con)
        Dim reader As SqlDataReader
        reader = cmd1.ExecuteReader()
        If (reader.Read()) Then
            ErrorProvider1.SetError(TextBox1, "此编号已存在，请重新输入！")
            TextBox1.Focus()

            e.Cancel = True

        Else
            ErrorProvider1.SetError(TextBox1, "")
        End If
        con.Close()
    End Sub

    Private Sub TextBox2_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs)
        If Not Regex.IsMatch(TextBox2.Text, "^[a-w]{2}") Then
            ErrorProvider1.SetError(TextBox2, "图书类型名称应由2位小写字母组成！")
            TextBox2.Focus()

            e.Cancel = True

            Return
        Else
            ErrorProvider1.SetError(TextBox2, "")
        End If

        con.Open()
        Dim cmd1 As New SqlCommand("select * from try where typename='" & Me.TextBox2.Text.Trim() & "'", con)
        Dim reader As SqlDataReader
        reader = cmd1.ExecuteReader()
        If (reader.Read()) Then
            ErrorProvider1.SetError(TextBox2, "此编号已存在，请重新输入！")
            TextBox2.Focus()

            e.Cancel = True

        Else
            ErrorProvider1.SetError(TextBox2, "")
            'f2 = True
        End If
        con.Close()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        con.Open()
        Dim cmd1 As New SqlCommand("insert into try values('" & TextBox1.Text & "','" & TextBox2.Text & "')", con)
        cmd1.ExecuteNonQuery()
        MsgBox("添加操作成功！", 64, "提示")
        con.Close()
        TextBox1.Text = ""
        TextBox2.Text = ""
    End Sub 

Answer 3

你在textBox1合法后把焦点放到textBox2上！

---

周雪峰