Question

public partial class Form1 : Form
{
    MyClass myClass = new MyClass("one", "two");

    public Form1()
    {
        InitializeComponent();
        textBox1.DataBindings.Add("Text", myClass, "Text1", false, DataSourceUpdateMode.Never);
        textBox2.DataBindings.Add("Text", myClass, "Text2", false, DataSourceUpdateMode.Never);
    }

    private void saveButton_Click(object sender, EventArgs e)
    {
        myClass.Text1 = textBox1.Text;
        myClass.Text2 = textBox2.Text;
        //textBox1.DataBindings["Text"].WriteValue();
        //textBox2.DataBindings["Text"].WriteValue();
    }
}

public class MyClass : INotifyPropertyChanged
{
    private string _Text1;
    private string _Text2;

    public event PropertyChangedEventHandler PropertyChanged;

    public string Text1
    {
        get { return _Text1; }
        set { _Text1 = value; OnPropertyChanged(new PropertyChangedEventArgs("Text1")); }
    }

    public string Text2
    {
        get { return _Text2; }
        set { _Text2 = value; OnPropertyChanged(new PropertyChangedEventArgs("Text2")); }
    }

    public MyClass(string text1, string text2)
    {
        Text1 = text1;
        Text2 = text2;
    }

    protected void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        if (PropertyChanged != null) PropertyChanged(this, e);
    }
}

I think is pretty clear what I’m trying to achieve. I want my form to save the changes made in my two TextBoxes to myClass. But whenever I press the save button after editing both text boxes, and saveButton_Click is invoked, the second textBox2‘s Text goes back to the original text (“two”). I tried using Binding‘s WriteValue function but the same thing happens. Using .net 4.0.

Edit Thanks for your answers, but I don’t need workarounds. I can find them myself. I just need to understand a little bit better how binding works. I would like to understand why is this happening?

Answer 1

Apparently, updating any value on the data source will cause all bindings to be updated. This explains the behavior (setting myClass.Text1 causes textBox2 to be updated with the current value of myClass.Text2). Unfortunately, the few posts I was able to find pretty much just said, “that’s how it works”.

One way to handle this is to create a BindingSource, set BindingSource.DataSource = myClass, and then bind your TextBoxes to the BindingSource.

BindingSource raises ListChanged events if the underlying data source is a list and items are added, removed, etc., or if the DataSource properties change. You can suppress these events by setting BindingSource.RaiseListChangedEvents to false, which would let you set multiple properties on myClass without data-binding updating the bound controls.

public partial class Form1 : Form
{
    MyClass myClass = new MyClass("one", "two");
    BindingSource bindingSource = new BindingSource();

    public Form1()
    {
        InitializeComponent();

        bindingSource.DataSource = myClass;

        textBox1.DataBindings.Add("Text", bindingSource, "Text1", true, DataSourceUpdateMode.Never);
        textBox2.DataBindings.Add("Text", bindingSource, "Text2", true, DataSourceUpdateMode.Never);                
    }

    private void button1_Click(object sender, EventArgs e)
    {
        bindingSource.RaiseListChangedEvents = false;
        myClass.Text1 = textBox1.Text;
        myClass.Text2 = textBox2.Text;
        bindingSource.RaiseListChangedEvents = true;
    }
}

HTH