【说明】 以下代码实现了当用户退出界面时，判断TextEdit中的文字是否发生改变，弹出对话框判断，让用户选择是否保存文件或取消退出界面操作。阅读下面的代码，将其补充完整。 【代码7-1】 Begin VB.Form Forml //...窗体描述(略) Begin VB.TextBox TextEditHeight = 1830Left = 180Tablndex= 0Text = "TextEdit"Top = 360Width = 3885 End //...窗体描述(略) End 【代码7-2】 Dim txtchange As Boolean Dim myval As String Private Sub Form Load () TextEdit.Text: "CIU, 中国软考联盟!" txtchange = False End Sub 【代码7-3】 Private Sub TextEdit_Change () Static notchange As Boolean (1) notchange = Tree End Sub Private Sub Form_Unload ( Cancel As Integer )Dim myval As StringIf (2) Then myval = MsgBox ( "保存文件的更改吗", vbYesNoCancel, "提示信息" ) If (3) ThenMsgBox "保存成功"End End If If (4) Then End If (5) Then Cancel = 1 End If End Sub