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VB.NET 2010 - A way to prevent certain characters from being copy pasted inside of a textbox?

Posted on 2011-02-21
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Last Modified: 2012-05-11
I have a simple method to prevent keypresses:

        If (e.KeyChar < "0" OrElse e.KeyChar > "9") Then
            e.Handled = True
            Exit Sub
        End If


Which goes in the keypress area. This will allow only 0 to 9 to be added.  However, it seems like you can copy paste other characters inside the text box. I know I can do things such as looping through each character each time the text is changed, but this seems like it would be a not a very efficient way of handling this issue. Pretty much the goal here is to always make sure the characters 0 to 9 are allowed, while still keeping functions like PASTING in tact without having it disabled completely.

This can go for a-Z, etc. Thanks!
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Question by:Valleriani
6 Comments
 
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Expert Comment

by:Jacco
ID: 34943086
You can set the property ShortcutsEnabled to false.

The way the context menu and the keyboard shortcuts are disabled.
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Expert Comment

by:Jacco
ID: 34943094
Didn't read correctly, sorry
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LVL 70

Accepted Solution

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Éric Moreau earned 300 total points
ID: 34943168
you can handle the TextChanged event and check the Text property against a regular expression as I shown in http://www.emoreau.com/Entries/Articles/2003/03/Creating-your-own-Windows-Custom-Control.aspx
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Assisted Solution

by:Jacco
Jacco earned 100 total points
ID: 34943324
Here is something working in C#.

All keys are exepted. And the cursorpos after last keypress is continuosly stored.

The new resulting string is accepted or rejected.

When rejected the last good entry is put back and the corresponding cursor position.

(Didn't test with selected parts and pasting illegal)
string prevok = "";
        int prevstrt = 0;
        bool inevent = false;

        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            prevstrt = textBox1.SelectionStart;
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            if (inevent) return;
            inevent = true;
            try
            {
                var sb = new StringBuilder();
                foreach (var c in textBox1.Text)
                    if (c >= '0' && c <= '9')
                        sb.Append(c);
                if (textBox1.Text != sb.ToString())
                {
                    textBox1.Text = prevok;
                    textBox1.SelectionStart = prevstrt;
                }
                else
                {
                    prevstrt = textBox1.SelectionStart;
                    prevok = textBox1.Text;
                }
            }
            finally
            {
                inevent = false;
            }
        }

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LVL 85

Assisted Solution

by:Mike Tomlinson
Mike Tomlinson earned 100 total points
ID: 34944353
You can trap the WM_PASTE message and act based on the pending input:
http://www.experts-exchange.com/Programming/Languages/.NET/Visual_Studio_.NET_2005/Q_23143054.html#20841606
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Author Closing Comment

by:Valleriani
ID: 34950671
Thank you. I think the regex was the best option here so it can handle everything. I was able to kill off the coding around keypress, and just use a regEX in textchange to prevent everything, including pasting.

Thanks!
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