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Creating a document with 'protected areas'

Author:	TX Text Control Support Department
Language:	Visual Basic, Visual Basic .NET
Version:	1.1
Released:	December 09, 2002
Last modified:	January 11, 2008
Requirements:	TX Text Control .NET with Visual Basic
Download code:	protected_areas.zip [30.18 KB, ZIP]

This week, we are going to show you how to create a document that has 'protected areas'. In this case, a 'protected area' is a part of the document that is read-only. The end-user cannot edit the contents of a protected area, but can still edit the rest of the document.

We are going do realize this effect by trapping the keystrokes to TX Text Control.

Please take a look at the following screenshot. To illustrate the protected areas, we have colored their background in gray. This is just for illustrative purposes only - the actual application does not gray-out the protected area.

Visual Basic 6

Private Sub TXTextControl1_KeyPress(KeyAscii As Integer)
	If mnu_options_readonly.Checked Then
		If Not TXTextControl1.TableAtInputPos <> 0 Then
			KeyAscii = 0
		Else
			If TXTextControl1.TableRowAtInputPos = 1 Then
				KeyAscii = 0
			End If
		End If
	End If
End Sub

Visual Basic .NET

Private Sub TxTextControl1_KeyPress(ByVal sender As
Object,ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TxTextControl1.KeyPress
	If mnuOptions_ReadOnly.Checked Then
		Dim table As TXTextControl.Table = TxTextControl1.Tables.GetItem
		If IsNothing(table) Then
			e.Handled = True
		Else
			If table.Columns.GetItem.Position =
			table.Columns.GetItem(1).Position Then
				e.Handled = True
			End If
		End If
	End If
End Sub

In the above code snippets, the user is only able to insert text into tables and not into the rest of the document (See the grayed-out areas of the above screenshot.)

Additionally, the first row (table header) cannot be edited. This is realized by checking the row at the current input position. The Visual Basic .NET sample shows how to protect a specific column of the table. If the current input position is not inside a table the KeyCode is set to 0. As we trap all keystrokes, the user is not able to insert text outside of a table.

We also have to trap the KeyDown event, because the user must not be able to paste text into the protected parts of the document. On the other hand, the user should be able to move the caret in the text:

Private Sub TXTextControl1_KeyDown(KeyCode As Integer, Shift As Integer)
	If mnu_options_readonly.Checked Then
		If Not TXTextControl1.TableRowAtInputPos > 1 Then
			If KeyCode <> vbKeyLeft And KeyCode <> vbKeyRight And KeyCode <>
			vbKeyUp And KeyCode <> vbKeyDown Then
				KeyCode = 0
			End If
		End If
	End If
End Sub

This sample can be also realized with marked text fields by using the FieldAtInputPos property instead of the TableAtInputPos property.

Complete code in Visual Basic 6 and Visual Basic .NET can be downloaded here:

We would like to offer you as much assistance with TX Text Control as you require. Please post all questions directly into the TX Text Control Support Forum.

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