Question

I have TextBox which allow insert only numeric values (filtering), But when I paste copied text it’s allow any kind of symbol. How can I prevent or filter text before pasting?

Answer 1

You could backup your text before any manual input and then when the input provided isn’t valid restore the previous text like so:

        _backupText = string.Empty;
        doNotPasteTextBox.TextInputStart += (sender, e) =>
                                                {
                                                    int textParsed;
                                                    if(int.TryParse(e.Text,out textParsed))
                                                    {
                                                        _backupText = doNotPasteTextBox.Text.Insert(doNotPasteTextBox.SelectionStart, e.Text);
                                                    }else
                                                    {
                                                        e.Handled = true;
                                                    }
                                                };

        doNotPasteTextBox.TextChanged += (sender, e) =>
                                             {
                                                 int textParsed;
                                                 int selectionStart = doNotPasteTextBox.SelectionStart;
                                                 if(!int.TryParse(doNotPasteTextBox.Text, out textParsed))
                                                 {
                                                     doNotPasteTextBox.Text = _backupText;
                                                 }
                                                 doNotPasteTextBox.SelectionStart = selectionStart;
                                             };

I wouldn’t recommend trying to capture the control keys or anything because when you’re on a mac or on linux then you’re screwed.

Adjust my sample and pour it inside a new textbox control to make it cleaner but you get the idea.