Question

In my VS 2012 WPF project, I have a customized textbox class called TextBoxDX that adds an AutoSelect feature. No problem. I have another class based on TextBoxDX called IntBox which only allows integers. That’s where our story begins. Both classes are used in binding situations like so:

<local:TextBoxDX Grid.Row="0" Grid.Column="1" x:Name="txtBox_singlesName" Width="320" HorizontalAlignment="left" Text="{Binding SelectedItem.name, ElementName=listBoxSingles, Mode=OneWay}"/>
<local:IntBox x:Name="intBox_heightin" Width="60" AllowZeroValue="True" MaxLength="2" Text="{Binding SelectedItem.heightin, ElementName=listBoxSingles, Mode=OneWay}" MinVal="0" MaxVal="11"/>

Pretty sure most of that is irrelevant except for the binding. Both work fine in that they change their text corresponding to ListBox selections. But in the IntBox class, I had to add code for allowing only integers. In order to do that, I tapped into the TextChanged event in my IntBox class. The end result is this:

using System;
using System.Text.RegularExpressions;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

 namespace Herculese
{
public class IntBox : TextBoxDX
{
    //INIT PROPERTIES
    private int _MaxVal = 0;
    private int _MinVal = 0;
    private bool _AllowZeroValue = false;

    //INIT STRING TO KEEP TRACK OF TEXT BEFORE CHANGES
    private string originalText;

    public IntBox()
    {
        //ADD TO TEXTCHANGED HANDLER
        TextChanged += new TextChangedEventHandler(My_OnTextChanged);

        //STORE ORIGINAL TEXT
        originalText = this.Text;
    }

    //EVENT HANDLER WHEN TEXT IS CHANGED

    private void My_OnTextChanged(object sender, EventArgs e)
    {
        //IF THERE IS TEXT IN THE BOX,
        MessageBox.Show("yee");
        if (this.Text.Length > 0)
        {
            //REMOVE SPACES AND LEADING ZEROS FROM STRING
            if (!_AllowZeroValue)
                this.Text = this.Text.TrimStart('0');
            this.Text = Regex.Replace(this.Text, @"\s+", "");

            //IF VALUE ISN'T NUMERICAL OR NOTHING IS LEFT AFTER REMOVING ZEROS AND SPACES, CHANGE TEXT BACK TO ORIGINAL
            Regex regex = new Regex("[^0-9]+");
            if (regex.IsMatch(this.Text) || this.Text.Length < 1)
            {
                this.Text = originalText;
                System.Media.SystemSounds.Beep.Play();
            }
            //IF VALUE IS NUMERICAL,
            else
            {
                //MAKE SURE VALUE IS WITHIN ACCEPTED RANGE. IF NOT, CHANGE IT TO HIGHEST/LOWEST AVAILABLE RESPECTIVELY
                int intText;
                intText = Convert.ToInt32(this.Text);
                if (intText > _MaxVal)
                {
                    this.Text = _MaxVal.ToString();
                    System.Media.SystemSounds.Beep.Play();
                }
                else if (intText < _MinVal)
                {
                    this.Text = _MinVal.ToString();
                    System.Media.SystemSounds.Beep.Play();
                }
                //SUCCESS!  UPDATE ORIGINAL TEXT WITH NEW VALID VALUE.
                else originalText = this.Text;
            }
        }
    }

    //PROVIDE GET/SET PROPERTIES
    public int MaxVal
    {
        get { return _MaxVal; }
        set { _MaxVal = value; }
    }
    public int MinVal
    {
        get { return _MinVal; }
        set { _MinVal = value; }
    }
    public bool AllowZeroValue
    {
        get { return _AllowZeroValue; }
        set { _AllowZeroValue = value; }
    }
}
}

As you can see, I had a great time in the TextChanged of my IntBox. Wild parties, you name it. Suddenly I realized that binding for IntBox wasn’t working anymore. I could manually change the text just fine. It only accepted integers and worked like a charm. But changing the ListBox selection no longer updated the text. If I removed the code in My_OnTextChanged, the binding worked again. I figured my code was causing the problem. So I came back today with a fresh head and realized something weird.

If I remove the code in My_OnTextChanged and replace it with a MessageBox, the binding works and the message box appears. Makes perfect sense and furthers the idea that my code is causing the issue. Now for the weirdness: if I put the code back into the event after the MessageBox code, binding is broken again and the MessageBox never shows meaning the event never fires. All I can say to that is… HUUUUH?! I’ve recreated this several times just to be sure I’m not crazy. The only other thing I could think of is a conflict with the TextBoxDX that it inherits from so I made it inherit directly from TextBox and got the same results… Anybody got a clue on this one?

Answer 1

You are assigning a new value to Text which is removing the original binding as you have replaced it with a new string.

Instead of using this.Text = "Somthing" try using base.SetCurrentValue(TextProperty, value);

Example:

//IF VALUE ISN'T NUMERICAL OR NOTHING IS LEFT AFTER REMOVING ZEROS AND SPACES, CHANGE TEXT BACK TO ORIGINAL
Regex regex = new Regex("[^0-9]+");
if (regex.IsMatch(this.Text) || this.Text.Length < 1)
{
    // this.Text = originalText;

    base.SetCurrentValue(TextProperty, originalText);
    System.Media.SystemSounds.Beep.Play();
}

SetCurrentValue Sets the value of a dependency property without changing its value source.