Question

我正在Visual Studio 2012中编写一个Visual Basic程序，我遇到了一个我无法自行解决的问题。我使用两个带有两个组合框的文本框。应用程序中没有按钮。我在输入数字时使用textchanged事件来触发计算。它将使用一个文本框，但当它在另一个文本框中显示答案时，它将触发文本框textchanged事件。因此，没有给我正确的答案。顺便说一句，这是一个转换长度的单位转换器，如米到毫米，米到英尺，米到英寸等......

Public Class frmMain
' class-scope variables
Dim decUnit1 As Decimal
Dim decUnit2 As Decimal
Dim intFlag As Integer

Private Sub frmMain_Load(sender As Object, e As EventArgs) Handles Me.Load
    PopCombo()
    cboUnitType.SelectedIndex = 0
End Sub

Private Sub PopCombo()
    ' populates the comboBoxes and sets default selection

    ' populate the comboBox accordingly
    If cboUnitType.SelectedIndex = 0 Then

        ClearBox()

        With Me.cbo1.Items
            .Add("Meter")
            .Add("Milimeter")
            .Add("Foot")
            .Add("Inch")
        End With

        With Me.cbo2.Items
            .Add("Meter")
            .Add("Milimeter")
            .Add("Foot")
            .Add("Inch")
        End With

        ' set default ComboBox index selection
        cbo1.SelectedIndex = 1
        cbo2.SelectedIndex = 3

    ElseIf cboUnitType.SelectedIndex = 1 Then

        ClearBox()

        With Me.cbo1.Items
            .Add("Celsius")
            .Add("Fahrenheit")
        End With

        With Me.cbo2.Items
            .Add("Celsius")
            .Add("Fahrenheit")
        End With

        cbo1.SelectedIndex = 0
        cbo2.SelectedIndex = 1

    End If

End Sub

Private Sub ClearBox()
    ' clears the comboBox
    cbo1.Items.Clear()
    cbo2.Items.Clear()
End Sub

Private Sub cboUnitType_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboUnitType.SelectedIndexChanged
    PopCombo()
End Sub

Private Sub txtUnit1_TextChanged(sender As Object, e As EventArgs) Handles txtUnit1.TextChanged

    Decimal.TryParse(txtUnit1.Text, decUnit1)
    Decimal.TryParse(txtUnit2.Text, decUnit2)

    If cboUnitType.SelectedIndex = 0 Then
        ' converts meter to...
        If cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 0 Then
            ' meter
            txtUnit2.Text = txtUnit1.Text
        ElseIf cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 1 Then
            ' millimeter
            txtUnit2.Text = (decUnit1 * 1000).ToString
        ElseIf cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 2 Then
            ' foot
            txtUnit2.Text = (decUnit1 * 3.28084).ToString
        ElseIf cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 3 Then
            ' inch
            txtUnit2.Text = (decUnit1 * 39.3701).ToString
        End If

        ' converts millimeter to...
        If cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 0 Then
            ' meter
            txtUnit2.Text = (decUnit1 * 0.001).ToString
        ElseIf cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 1 Then
            ' millimeter
            txtUnit2.Text = txtUnit1.Text
        ElseIf cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 2 Then
            ' foot
            txtUnit2.Text = (decUnit1 * 0.00328084).ToString
        ElseIf cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 3 Then
            ' inch
            txtUnit2.Text = (decUnit1 * 0.0393701).ToString
        End If

        ' converts foot to...
        If cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 0 Then
            ' meter
            txtUnit2.Text = (decUnit1 * 0.3048).ToString
        ElseIf cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 1 Then
            ' millimeter
            txtUnit2.Text = (decUnit1 * 304.8).ToString
        ElseIf cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 2 Then
            ' foot
            txtUnit2.Text = txtUnit1.Text
        ElseIf cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 3 Then
            ' inch
            txtUnit2.Text = (decUnit1 * 12).ToString
        End If

        ' converts inch to...
        If cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 0 Then
            ' meter
            txtUnit2.Text = (decUnit1 * 0.0254).ToString
        ElseIf cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 1 Then
            ' millimeter
            txtUnit2.Text = (decUnit1 * 25.4).ToString
        ElseIf cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 2 Then
            ' foot
            txtUnit2.Text = (decUnit1 * 0.0833333).ToString
        ElseIf cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 3 Then
            ' inch
            txtUnit2.Text = txtUnit1.Text
        End If
    End If

End Sub

Private Sub txtUnit2_TextChanged(sender As Object, e As EventArgs) Handles txtUnit2.TextChanged

    Decimal.TryParse(txtUnit1.Text, decUnit1)
    Decimal.TryParse(txtUnit2.Text, decUnit2)

    If cboUnitType.SelectedIndex = 0 Then
        ' converts meter to...
        If cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 0 Then
            ' meter
            txtUnit1.Text = txtUnit2.Text
        ElseIf cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 0 Then
            ' millimeter
            txtUnit1.Text = (decUnit2 * 1000).ToString
        ElseIf cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 0 Then
            ' foot
            txtUnit1.Text = (decUnit2 * 3.28084).ToString
        ElseIf cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 0 Then
            ' inch
            txtUnit1.Text = (decUnit2 * 39.3701).ToString
        End If

        ' converts millimeter to...
        If cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 1 Then
            ' meter
            txtUnit1.Text = (decUnit2 * 0.001).ToString
        ElseIf cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 1 Then
            ' millimeter
            txtUnit1.Text = txtUnit2.Text
        ElseIf cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 1 Then
            ' foot
            txtUnit1.Text = (decUnit2 * 0.00328084).ToString
        ElseIf cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 1 Then
            ' inch
            txtUnit1.Text = (decUnit2 * 0.0393701).ToString
        End If

        ' converts foot to...
        If cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 2 Then
            ' meter
            txtUnit1.Text = (decUnit2 * 0.3048).ToString
        ElseIf cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 2 Then
            ' millimeter
            txtUnit1.Text = (decUnit2 * 304.8).ToString
        ElseIf cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 2 Then
            ' foot
            txtUnit1.Text = txtUnit2.Text
        ElseIf cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 2 Then
            ' inch
            txtUnit1.Text = (decUnit2 * 12).ToString
        End If

        ' converts inch to...
        If cbo1.SelectedIndex = 0 AndAlso cbo2.SelectedIndex = 3 Then
            ' meter
            txtUnit1.Text = (decUnit2 * 0.0254).ToString
        ElseIf cbo1.SelectedIndex = 1 AndAlso cbo2.SelectedIndex = 3 Then
            ' millimeter
            txtUnit1.Text = (decUnit2 * 25.4).ToString
        ElseIf cbo1.SelectedIndex = 2 AndAlso cbo2.SelectedIndex = 3 Then
            ' foot
            txtUnit1.Text = (decUnit2 * 0.0833333).ToString
        ElseIf cbo1.SelectedIndex = 3 AndAlso cbo2.SelectedIndex = 3 Then
            ' inch
            txtUnit1.Text = txtUnit1.Text
        End If
    End If

End Sub

End Class

Answer 1

在更新文本框的Text属性时，您需要使用布尔变量或两个来抑制文本更改事件。这是一个将度数F转换为C并返回的示例，并允许您在任一文本框中键入值：

Public Class Form4

    Dim suppressTextBox1TextChanged As Boolean = False
    Dim suppressTextBox2TextChanged As Boolean = False

    Private Sub txtDegreesF_TextChanged(sender As System.Object, e As System.EventArgs) Handles txtDegreesF.TextChanged
        'Convert to Celsius

        'Only do the calculation if we are typing the textbox
        If Not suppressTextBox1TextChanged Then
            Dim degreesF As Double
            Dim degreesC As Double
            If Double.TryParse(txtDegreesF.Text, degreesF) Then
                degreesC = (degreesF - 32) * (5 / 9)
                suppressTextBox2TextChanged = True
                txtDegreesC.Text = degreesC.ToString()
                suppressTextBox2TextChanged = False
            End If
        End If

    End Sub

    Private Sub txtDegreesC_TextChanged(sender As System.Object, e As System.EventArgs) Handles txtDegreesC.TextChanged
        'Convert to Fahrenheit

        'Only do the calculation if we are typing the textbox
        If Not suppressTextBox2TextChanged Then
            Dim degreesF As Double
            Dim degreesC As Double
            If Double.TryParse(txtDegreesC.Text, degreesC) Then
                degreesF = (degreesC * 1.8) + 32
                suppressTextBox1TextChanged = True
                txtDegreesF.Text = degreesF.ToString()
                suppressTextBox1TextChanged = False
            End If
        End If
    End Sub
End Class

如何防止在Visual Basic中发生第二个textchanged事件

1 个答案: