TextBoxBase.Clear 方法

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

从文本框控件中清除所有文本。

public:
 void Clear();

public void Clear ();

member this.Clear : unit -> unit

Public Sub Clear ()

示例

下面的代码示例使用 TextBox（派生类）为 TextChanged 事件创建事件处理程序。 事件处理程序中的代码将数据限制为数字。 在 控件中输入文本后，代码将确定输入的文本是否为数字。 如果文本不是数字，则代码将清除控件中的文本，并显示 ， MessageBox 以提醒用户仅接受数字。 此示例要求 Boolean 在此方法外部定义名为 flag 的变量和 TextBox 名为 textBox1 的控件。 此示例演示如何使用标志变量来避免事件中的 TextChanged 级联事件。

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

注解

可以使用此方法清除控件的内容，而不是为 属性分配 Text 一个空字符串。

另请参阅

• Cut()
• Copy()
• Paste()
• CanUndo
• ClearUndo()