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POHow to prevent a second textchanged event from occurring in Visual Basic
 

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  1. POHow to prevent a second textchanged event from occurring in Visual Basic
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    <p>I am writing a Visual Basic program in Visual Studio 2012, and I have ran into a problem that I just cannot fix on my own. I am using two text boxes with two combo boxes. There are no buttons in the application. I am using the textchanged event to trigger the calculation as you type in numbers. It will work using one text box, but when it displays the answer in the other text box, it is triggering the text boxes textchanged event. Therefore, not giving me the correct answer. By the way, this is a unit converter that is converting length such as meter to millimeter, meter to foot, meter to inch, etc...</p> <pre><code>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 </code></pre>
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    1. USPlutonix
    1. USZack
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    1. COput the event code into called functions perhaps passing the textbox values as params and return a value (the answer) then when you go to post the answer, set an Ignore flag so that you are not responding to your own changes. WHen the flag is true, dont call the new procs. (Basically need to isolate the calcs from the events so you can break the cycle). Might be easier to just add a Calc button.
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      1. POHow to prevent a second textchanged event from occurring in Visual Basic
      1. USPlutonix
    2. COCould you give me some example code of this Ignore Flag? Thanks in advance.
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      1. POHow to prevent a second textchanged event from occurring in Visual Basic
      1. USZack
    3. COYou have recursive events here, the txtUnit1 event handler modifies txtUnit2. Which will trigger the event for txtUnit2 which modifies txtUnit1 again. This is normally a fatal mishap that crashes your program but it should in fact work here. Since the conversion back should produce the exact same text as is already in the textbox so the event should not fire. Use a debugger to find out why the text doesn't match. Pretty good debugging learning exercise btw, the point of this assignment presumably :)
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      1. POHow to prevent a second textchanged event from occurring in Visual Basic
      1. USHans Passant
 

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