How to add a numeric textbox in WP7 which can take a float value?

Question

I am developing WP7 application. I am new to the WP7. I am also new to the silverlight. I have a textbox in my application. In this textbox user enters the amount. I want to give the facility in my application so that user can enter the float amount ( for e.g. 1000.50 or 499.9999). The user should be able to enter either two digit or four digit after the '.' .My code for the textbox is as follows.

<TextBox InputScope="Number" Height="68" HorizontalAlignment="Left" Margin="-12,0,0,141" Name="AmountTextBox" Text="" VerticalAlignment="Bottom" Width="187" LostFocus="AmountTextBox_LostFocus" BorderBrush="Gray" MaxLength="10"/>

I have done the following validations for the above textbox.

public void AmountTextBox_LostFocus(object sender, RoutedEventArgs e)
        {
            foreach (char c in AmountTextBox.Text)
            {                
                if (!char.IsDigit(c))
                {
                    MessageBox.Show("Only numeric values are allowed");
                    AmountTextBox.Focus();
                    return;
                }
            }
        }

How to resolve the above issue. Can you please provide me any code or link through which I can resolve the above issue. If I am doing anything wrong then please guide me.

Answer 1

The following code is working fine for me. I have tested it in my application. In the following code by adding some validations we can treat our general textbox as a numeric textbox which can accept the float values.

public void AmountTextBox_LostFocus(object sender, RoutedEventArgs e)
        {
            foreach (char c in AmountTextBox.Text)
            {                
                if (!char.IsDigit(c) && !(c == '.'))
                {
                    if (c == '-')
                    {
                        MessageBox.Show("Only positive values are allowed");
                        AmountTextBox.Focus();
                        return;
                    }

                    MessageBox.Show("Only numeric values are allowed");
                    AmountTextBox.Focus();
                    return;
                }
            }

            string [] AmountArr = AmountTextBox.Text.Split('.');
            if (AmountArr.Count() > 2)
            {
                MessageBox.Show("Only one decimal point are allowed");
                AmountTextBox.Focus();
                return;
            }

            if (AmountArr.Count() > 1)
            {
                int Digits = AmountArr[1].Count();
                if (Digits > 2)
                {
                    MessageBox.Show("Only two digits are allowed after decimal point");
                    AmountTextBox.Focus();
                    return;
                }
            }
        }

Answer 2

Download the free book Programming Windows Phone 7 by Charles Petzold. On page 380, in section TextBox Binding Updates, under Chapter 12: Data Bindings, he has an excellent example on validating floating point input.

For limiting the user input to 2 or 4 decimal places you'll have to add some logic to TextBox's TextChanged callback. For instance, you could convert the float to a string, search for the decimal and then figure out the length of the string to the right of the decimal.

On the other hand, if you just want to round the user input to 2 or 4 digits, take a look at the Fixed-Point ("F") Format Specifier section on this page.

Answer 3

You can always use this regex [-+]?[0-9].?[0-9] to determine if its a floating number.

public void AmountTextBox_LostFocus(object sender, RoutedEventArgs e)
  {
      Regex myRange = new Regex(@"[-+]?[0-9]*\.?[0-9]");
      if (myRange.IsMatch(textBox1.Text))
        // Match do whatever
      else
        // No match do whatever
  }

Answer 4

I do the validation this way as shown in the code below.

No need for checking char by char and user culture is respected!

namespace Your_App_Namespace
{
public static class Globals
{
    public static double safeval = 0; // variable to save former value!

    public static bool isPositiveNumeric(string strval, System.Globalization.NumberStyles NumberStyle)
    // checking if string strval contains positive number in USER CULTURE NUMBER FORMAT!
    {
        double result;
        boolean test;
        if (strval.Contains("-")) test = false;
        else test = Double.TryParse(strval, NumberStyle, System.Globalization.CultureInfo.CurrentCulture, out result);
        // if (test == false) MessageBox.Show("Not positive number!");
        return test;
    }

    public static string numstr2string(string strval, string nofdec)
    // conversion from numeric string into string in USER CULTURE NUMBER FORMAT!
    // call example numstr2string("12.3456", "0.00") returns "12.34"
    {
        string retstr = "";
        if (Globals.isPositiveNumeric(strval, System.Globalization.NumberStyles.Number)) retstr = double.Parse(strval).ToString(nofdec);
        else retstr = Globals.safeval.ToString(nofdec);
        return retstr;
    }

    public static string number2string(double numval, string nofdec)
    // conversion from numeric value into string in USER CULTURE NUMBER FORMAT!
    // call example number2string(12.3456, "0.00") returns "12.34"
    {
        string retstr = "";
        if (Globals.isPositiveNumeric(numval.ToString(), System.Globalization.NumberStyles.Number)) retstr = numval.ToString(nofdec);
        else retstr = Globals.safeval.ToString(nofdec);
        return retstr;
    }
}

// Other Your_App_Namespace content

}

// This the way how to use those functions in any of your app pages

    // function to call when TextBox GotFocus

    private void textbox_clear(object sender, System.Windows.RoutedEventArgs e)
    {
        TextBox txtbox = e.OriginalSource as TextBox;
        // save original value
        Globals.safeval = double.Parse(txtbox.Text);
        txtbox.Text = "";
    }

    // function to call when TextBox LostFocus

    private void textbox_change(object sender, System.Windows.RoutedEventArgs e)
    {
        TextBox txtbox = e.OriginalSource as TextBox;
        // text from textbox into sting with checking and string format
        txtbox.Text = Globals.numstr2string(txtbox.Text, "0.00");
    }