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TextBoxBase.Clear Method

Clears all text from the text box control.

[Visual Basic]
Public Sub Clear()
[C#]
public void Clear();
[C++]
public: void Clear();
[JScript]
public function Clear();

Remarks

You can use this method to clear the contents of the control instead of assigning the Text property an empty string.

Example

[Visual Basic, C#, C++] The following example uses TextBox, a derived class, to create an event handler for the TextChanged event. The code within the event handler restricts data to numbers. After text has been entered in the control, the code determines if the text entered is a number. If the text is not a number, the code clears the text from the control and a MessageBox is displayed to alert the user that only numbers are accepted. The example assumes that a Boolean variable named flag and a TextBox control called textBox1 are defined outside of this method. This example demonstrates how to use a flag variable to avoid a cascading event in the TextChanged event.

[Visual Basic] 
Private flag As Boolean    

Private Sub MyTextChangedHandler(sender As System.Object, e As System.EventArgs)
    ' Check the flag to prevent code re-entry. 
    If flag = False Then
        ' Set the flag to True to prevent re-entry of the code below.
        flag = True
        ' Determine if the text of the control is a number.
        If IsNumeric(textBox1.Text) = False Then
            ' Display a message box and clear the contents if not a number.
            MessageBox.Show("The text is not a valid number. Please re-enter")
            ' Clear the contents of the text box to allow re-entry.
            textBox1.Clear()
        End If
        ' Reset the flag so other TextChanged events are processed correctly.
        flag = False
    End If
End Sub


[C#] 
private bool flag;

public void MyTextChangedHandler(System.Object sender, System.EventArgs e)
{
    long val;    
    // Check the flag to prevent code re-entry. 
    if(flag == false)
    {
       // Set the flag to True to prevent re-entry of the code below.
       flag = true;
       // Determine if the text of the control is a number.
       try {
          // Attempt to convert to long
          val = System.Convert.ToInt64(textBox1.Text);
       }
       catch {
          // Display a message box and clear the contents if not a number.
          MessageBox.Show("The text is not a valid number. Please re-enter");
          // Clear the contents of the text box to allow re-entry.
          textBox1.Clear();
       }
       // Reset the flag so other TextChanged events are processed correctly.
       flag = false;
    }        
 }
 

[C++] 
private:
bool flag;

public:
void MyTextChangedHandler(System::Object* /*sender*/, System::EventArgs* /*e*/)
{
    Int64 val;    
    // Check the flag to prevent code re-entry. 
    if(flag == false)
    {
       // Set the flag to True to prevent re-entry of the code below.
       flag = true;
       // Determine if the text of the control is a number.
       try {
          // Attempt to convert to long
          val = System::Convert::ToInt64(textBox1->Text);
       }
       catch (Exception*) {
          // Display a message box and clear the contents if not a number.
          MessageBox::Show(S"The text is not a valid number. Please re-enter");
          // Clear the contents of the text box to allow re-entry.
          textBox1->Clear();
       }
       // Reset the flag so other TextChanged events are processed correctly.
       flag = false;
    }        
 }
 

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

TextBoxBase Class | TextBoxBase Members | System.Windows.Forms Namespace | Cut | Copy | Paste | CanUndo | ClearUndo

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