Winforms Textbox with two way DataBinding not working as it should be

Question

Winforms has two Textboxes. textBox2 is binded to a property Unit. I wish that any changes made to Unit or textBox2 will automatically update textBox2 or Unit respectively. But it does not. Here are three versions of the code for a Winform.

Version one set data binding, hope it will have two ways auto update but does not work

public partial class Receiver : Form, INotifyPropertyChanged
{         

    private int unit=0;
    public int Unit
    {
        get { return unit; }
        set
        {
            if (value != unit)
            {
                unit = value;                                          
            }
        }
    }

    public Receiver()
    {
        InitializeComponent();            
        textBox2.DataBindings.Add("Text", Unit, "Unit");
    }

    private void textBox1_TextChanged(object sender, EventArgs e)
    {   
        //textBox1 change makes Unit change, 
        //I wish the change will be displayed in textBox2 automatically
        Unit = Convert.ToInt32(textBox1.Text);
    }        
}

Version two with event handler, hard code to update textBox2 with the event handler

but change textBox2 still will not update Unit automatically

public partial class Receiver : Form, INotifyPropertyChanged
{ 
    public event PropertyChangedEventHandler PropertyChanged;

    private int unit=0;
    public int Unit
    {
        get { return unit; }
        set
        {
            if (value != unit)
            {
                unit = value;                       
                if (PropertyChanged != null)
                {
                   PropertyChanged(this, new PropertyChangedEventArgs(info));
                }  
            }
        }
    }

    public Receiver()
    {
        InitializeComponent();            
        textBox2.DataBindings.Add("Text", this.Unit, "Unit", false, 
                                                 DataSourceUpdateMode.OnPropertyChanged);
        PropertyChanged += new PropertyChangedEventHandler(OnPropertyChanged);

    }    

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        Unit = Convert.ToInt32(textBox1.Text);
    }


    private void OnPropertyChanged(object sender, EventArgs e)
    {  
        //this actually is hard coded to update textBox2, binding does no help
        textBox2.Text = Unit.ToString();
    }
}

Version three why use event handler, we can simply do this way.

public partial class Receiver : Form, INotifyPropertyChanged
{ 
    private int unit=0;
    public int Unit
    {
        get { return unit; }
        set
        {
            if (value != unit)
            {
                unit = value;   
                textBox2.text = unit.toString();                          
            }
        }
    }

    public Receiver()
    {
        InitializeComponent();            
        textBox2.DataBindings.Add("Text", Unit, "Unit");
    }

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        Unit = Convert.ToInt32(textBox1.Text);           
    }   

    private void textBox2_TextChanged(object sender, EventArgs e)
    {
        Unit = Convert.ToInt32(textBox2.Text);           
    } 
}

}

Version two and Version three have a problem, any changes to textbox1 will cause update in textbox2 . That will cause a lot of CPU cycle. The best way is when the mouse focus leaves textBox1 then do the update. So how to do it?

Answer 1

The problem in your code is at line:

textBox2.DataBindings.Add("Text", Unit, "Unit");

You should replace the data source by the instance that holds that property not the property itself, and here you should also specify the data source update mode set it to DataSourceUpdateMode.OnPropertyChanged . So:

textBox2.DataBindings.Add("Text", this, "Unit", false, DataSourceUpdateMode.OnPropertyChanged);

//test using the second or the third approach:
Unit = 15;//now the textBox2.Text equals to 15 too.

textBox2.Text = 12;//now Unit equals 12 too