Restricting a WPF Textbox to integers by swallowing an exception

Question

I've written the following to restrict a WPF textbox to only accept integers and also only accept a number less than or equal to 35:

In my WindowLoaded event I create a handler for 'OnPaste':

DataObject.AddPastingHandler(textBoxWorkflowCount, OnPaste);

OnPaste consists of the following:

private void OnPaste(object sender, DataObjectPastingEventArgs e)
{
    if (!IsNumeric(e.Source.ToString(), NumberStyles.Integer)) e.Handled = true;
}

and our function to force numerics only is as follows:

public bool IsNumeric(string val, NumberStyles numberStyle)
{
    double result;
    return double.TryParse(val, numberStyle, CultureInfo.CurrentCulture, out result);
}

The specific textbox that is having the error should also be limited to a number <=35. To do this I've added the following TextChanged event:

private void TextBoxWorkflowCountTextChanged(object sender, TextChangedEventArgs e)
        {
            try
            {
                if (textBoxWorkflowCount == null || textBoxWorkflowCount.Text == string.Empty || Convert.ToInt32(textBoxWorkflowCount.Text) <= 35) return;
                MessageBox.Show("Number of workflow errors on one submission cannot be greater then 35.", "Workflow Count too high", MessageBoxButton.OK, MessageBoxImage.Warning);
                textBoxWorkflowCount.Text = "";
            }
            catch(Exception)
            {
                // todo: Oh the horror! SPAGHETTI! Must fix. Temporarily here to stop 'pasting of varchar' bug
                if (textBoxWorkflowCount != null) textBoxWorkflowCount.Text = "";
            }

        }

Although this does the job and works it's very nasty/hackish and I would love to know how it could be done better for sake of improving myself... Especially so without having to swallow an exception.

See http://stackoverflow.com/questions/382676/good-numericupdown-equivalent-in-wpf — Chris Shain, Aug 14 '12 at 03:30
@ChrisShain Doesn't seem relevant to my case? Could you explain how you see the two as being related, I'm missing it? — Michael A, Aug 14 '12 at 03:35
@codesparkle I do - but wasn't sure if this was a better home for it? Is it better if I move it over there? — Michael A, Aug 14 '12 at 03:40
I reckon it would fit there really well. If the moderators agree, they will migrate it, you needn't take any action. — Adam, Aug 14 '12 at 03:42

score 1 · Accepted Answer · answered Aug 14 '12 at 03:54

Does this work for you? Replace the content of TextBoxWorkflowCountTextChanged with this:

if (textBoxWorkflowCount == null || textBoxWorkflowCount.Text == string.Empty) return;
int workflowcount = 36;
if (int.TryParse(textBoxWorkflowCount.Text, out workflowcount) && workflowcount > 35) {
    MessageBox.Show("Number of workflow errors on one submission cannot be greater then 35.", "Workflow Count too high", MessageBoxButton.OK, MessageBoxImage.Warning);
    textBoxWorkflowCount.Text = "";
}
else if (workflowcount == 36) {
    textBoxWorkflowCount.Text = "";
}

Michael A · Answer 2 · 2012-08-14T04:45:43.370

1

Based on of QtotheC's, answer I arrived at the following after a bit more refactoring. Adding here for future visitors :)

    private void TextBoxWorkflowCountTextChanged(object sender, TextChangedEventArgs e)
    {
        if (string.IsNullOrEmpty(textBoxWorkflowCount.Text))
            return;

        int workflowCount;

        if (!int.TryParse(textBoxWorkflowCount.Text, out workflowCount) || workflowCount <= 35) return;
        MessageBox.Show("Number of workflow errors on one submission cannot be greater then 35.", "Workflow Count too high",
                        MessageBoxButton.OK, MessageBoxImage.Warning);
        textBoxWorkflowCount.Text = "35";
    }

edited Aug 14 '12 at 04:45

answered Aug 14 '12 at 04:07

Michael A

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you *could* combine the two conditions with || (that would reduce nesting). – Adam Aug 14 '12 at 04:33
@codesparkle Don't you mean && for the second if statement? Will edit / update with thatn ow. – Michael A Aug 14 '12 at 04:43
It's ok, just to be cheeky I inverted so I could use || :) – Michael A Aug 14 '12 at 04:45
You'd have a `NullPointerException` at `string.IsNullOrEmpty(textBoxWorkflowCount.Text)` if `textBoxWorkflowCount` is ever null. Not that it will matter much--this event should never fire if the textbox is null. – Qi Chen Aug 14 '12 at 16:04

Restricting a WPF Textbox to integers by swallowing an exception

2 Answers2