DataGrid and Observable Collection in WPF

Question

I have a datagrid like below in my WPF application.

Answer 1

When creating your own UI in DataGridTemplateColumn (or a custom DataGrid.RowStyle for that matter), the DataGrid changes the UpdateSourceTrigger (i.e. when the underlying data should be updated) on all your bindings to Explicit if you didn't specify them yourself.

That "feature" is described briefly here: 5 Random Gotchas with the WPF DataGrid, and even though the author says this happens whether or not you set the UpdateSourceTrigger yourself, setting it yourself does actually work (at least in .Net 4.0).

Use LostFocus to mimic the default TextBox behavior (and PropertyChanged on CheckBox etc):

...
<TextBox Text="{Binding Column1, UpdateSourceTrigger=LostFocus}"></TextBox>
...
<TextBox Text="{Binding Column2, UpdateSourceTrigger=LostFocus}"></TextBox>
...

Answer 2

There are a couple of side notes I would like to make.
1) You dont need to have a setter on your TestSource property. You set this value once, and before the DataContext is set, so this is pointless.
2) You dont implement INotifyPropertyChanged on the Test class
3) You load the data on the UI thread. This can cause the App to freeze (become unresponsive) while the Data is being loaded.

Try updating the C# code to the below:

namespace MyApp
{
    public partial class TestWindow: Window
    {
        private ObservableCollection<Test> _testSource = new ObservableCollection<Test>();


        public TestWindow()
        {
            InitializeComponent();

            //NOTE: this blocks the UI thread. Slow DB/Network will freeze the App while we wait. 
            // This should be done on a background thread.
            string strConnString = Application.Current.Properties["connectionStr"].ToString();
            SqlConnection con = new SqlConnection(strConnString);
            SqlCommand cmd = new SqlCommand("SELECT Column1,Column2 FROM MyTable", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataTable dtTest = new DataTable();
            da.Fill(dtTest);
            foreach (DataRow row in dtTest)
            {
                Test cd = new Test();
                cd.Column1 = row["Column1"].ToString();
                cd.Column2 = row["Column2"].ToString();
                TestSource.Add(cd);
            }
            this.DataContext = this;
        }

        public ObservableCollection<Test> TestSource { get { return _testSource; } }

        private void SaveButton_Click(object sender, RoutedEventArgs e)
        {
            var rowIdx = 0;
            foreach(var t in TestSource)
            {
                string a = t.Column1;
                string b = t.Column2;

                Console.WriteLine("Row {0}, col1='{1}', col2='{2}'", rowIdx++, a, b);
            }
        }
    }

    public sealed class Test : INotifyPropertyChanged
    {
        private string _column1;
        private string _column2;

        public string Column1
        { 
            get{return _column1;}
            set
            {
                if(_column1!=value)
                {
                    _column1 = value;
                    OnPropertyChanged("Column1");
                }
            }           
        }
        public string Column2
        { 
            get{return _column2;}
            set
            {
                if(_column2!=value)
                {
                    _column2 = value;
                    OnPropertyChanged("Column2");
                }
            }           
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propName)
        {
            var handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propName));
            }
        }
    }
}

You may also want to update the Binding to twoway, however I do think this is the default.

<TextBox Text="{Binding Column1, Mode=TwoWay}" />