TextBoxBase.Clear 方法

定義

將所有文字從文字方塊控制項清除。Clears all text from the text box control.

public:
 void Clear();
public void Clear ();
member this.Clear : unit -> unit
Public Sub Clear ()

範例

下列程式碼範例會使用 TextBox 衍生類別(衍生類別)來建立事件的事件處理常式 TextChangedThe following code example uses TextBox, a derived class, to create an event handler for the TextChanged event. 事件處理常式中的程式碼會將資料限制為數字。The code within the event handler restricts data to numbers. 在控制項中輸入文字後,程式碼會判斷輸入的文字是否為數字。After text has been entered in the control, the code determines if the text entered is a number. 如果文字不是數位,則程式碼會清除控制項中的文字,並 MessageBox 顯示,以警告使用者只接受數位。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. 此範例需要在 Boolean flag TextBox textBox1 這個方法之外定義名為的變數和呼叫的控制項。The example requires that a Boolean variable named flag and a TextBox control called textBox1 are defined outside of this method. 這個範例示範如何使用旗標變數來避免事件中的串聯事件 TextChangedThis example demonstrates how to use a flag variable to avoid a cascading event in the TextChanged event.

private:
   bool flag;

private:
   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( "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;
      }
   }
private bool flag;

private 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;
    }        
 }
 
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

備註

您可以使用這個方法來清除控制項的內容,而不是將 Text 空字串指派給屬性。You can use this method to clear the contents of the control instead of assigning the Text property an empty string.

適用於

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