C＃-TextBox_TextChanged事件-恢復為先前的值

Question

我將在TextBox_TextChanged事件上發布一個確認對話框。 如果用戶單擊“否”，則我想以某種方式將文本框還原為其舊值（即在更改之前），但是在觸發事件時，TextBox.Text已經是更改后的值...是有沒有辦法保存或獲得舊的價值？

贊賞任何想法或方法。 謝謝！

這是我的代碼：

private void txtFCServerURL_TextChanged(object sender, EventArgs e)
    {
            DialogResult clearGrid = MessageBox.Show("Changing the text will clear the grid. Are you sure?", "Confirmation", MessageBoxButtons.YesNo);
            if (clearGrid == DialogResult.Yes)
            {
                for (int i = 0; i < dgvGrid.Rows.Count; i++)
                {
                    dgvGrid.Rows.RemoveAt(0);
                }
            }
            else txtFCServerURL.Text = [TEXT BEFORE CHANGE]
    }

Answer 1

選項1：一個文本框有一個Undo方法。 這是一個帶有代碼示例的鏈接：

http://msdn.microsoft.com/zh-cn/library/system.windows.forms.textboxbase.undo%28v=vs.110%29.aspx

為了簡化起見，這是鏈接中的示例：

private void Menu_Copy(System.Object sender, System.EventArgs e)


{
    // Ensure that text is selected in the text box.    
    if(textBox1.SelectionLength > 0)
        // Copy the selected text to the Clipboard.
        textBox1.Copy();
 }

 private void Menu_Cut(System.Object sender, System.EventArgs e)
 {   
     // Ensure that text is currently selected in the text box.    
     if(textBox1.SelectedText != "")
        // Cut the selected text in the control and paste it into the Clipboard.
        textBox1.Cut();
 }

 private void Menu_Paste(System.Object sender, System.EventArgs e)
 {
    // Determine if there is any text in the Clipboard to paste into the text box. 
    if(Clipboard.GetDataObject().GetDataPresent(DataFormats.Text) == true)
    {
        // Determine if any text is selected in the text box. 
        if(textBox1.SelectionLength > 0)
        {
          // Ask user if they want to paste over currently selected text. 
          if(MessageBox.Show("Do you want to paste over current selection?", "Cut Example", MessageBoxButtons.YesNo) == DialogResult.No)
             // Move selection to the point after the current selection and paste.
             textBox1.SelectionStart = textBox1.SelectionStart + textBox1.SelectionLength;
        }
        // Paste current text in Clipboard into text box.
        textBox1.Paste();
    }
 }


 private void Menu_Undo(System.Object sender, System.EventArgs e)
 {
    // Determine if last operation can be undone in text box.    
    if(textBox1.CanUndo == true)
    {
       // Undo the last operation.
       textBox1.Undo();
       // Clear the undo buffer to prevent last action from being redone.
       textBox1.ClearUndo();
    }
 }

選項2：如果只需要最后一個文本（意味着僅向后退一步），則可以使用文本更改事件在更改之前用當前文本更新字符串變量，然后可以在任何需要的地方使用它。

Answer 2

我會做的（不確定是否是最好的選擇）是做一個變量並在TextChanged的末尾設置其值。 這樣，下一次它將進入TextChanged時，您仍將具有先前更改的值。

 string txt = "";
    private void txtFCServerURL_TextChanged(object sender, EventArgs e)
        {
              if(txtFCServerURL.Text != txt)
               {
                 DialogResult clearGrid = MessageBox.Show("Changing the text will clear the grid. Are you sure?", "Confirmation", MessageBoxButtons.YesNo);
                 if (clearGrid == DialogResult.Yes)
                 {
                    for (int i = 0; i < dgvGrid.Rows.Count; i++)
                    {
                        dgvGrid.Rows.RemoveAt(0);
                    }
                 }
                 else txtFCServerURL.Text = txt;
               }
        }