Concept of "UpdateSourceTrigger" Property, How to use it in WPF?

I have a TextBlock, binded with an Object and when i update property of object its not refleting on UI, Why ?

Code:

In Windows1.xaml

<TextBlock Name="txtName" Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" Width="100" Height="20" Margin="12,23,166,218" />

and In Windows.xaml.cs

public partial class Window1 : Window
{
    Employee obj ;
    public Window1()
    {            
        InitializeComponent();
        obj = new Employee();
        obj.Name = "First";
        txtName.DataContext = obj;
    }

    private void btnUpdate_Click(object sender, RoutedEventArgs e)
    {开发者_StackOverflow
        obj.Name = "changed";            
    }
}
public class Employee : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private string _name;
    public string Name
    {
        set 
        {
            this._name = value;
            OnPropertyChanged(Name);
        }
        get { return this._name; }
    }

    protected void OnPropertyChanged(string name)
    {

        PropertyChangedEventHandler handler = PropertyChanged;

        if (handler != null)
        {

            handler(this, new PropertyChangedEventArgs(name));

        }

    }        
}

OnPropertyChanged(Name);

should be:

OnPropertyChanged("Name");

otherwise if the name is set to "Kent", you're raising a property changed event saying that the "Kent" property has changed, which obviously doesn't exist.

As for UpdateSourceTrigger, that only applies to the source. The property you've bound is the target, not the source. And it doesn't make sense for a TextBlock to update its source, because there's no way for the user to modify the TextBlock text. A TextBox, on the other hand, would make sense. In that case, UpdateSourceTrigger determines the point at which the text in the TextBox is pushed back to the source property (e.g. as the user types each character, or when they move away from the TextBox).

Pass the name of the property as string, instead of the property value, like so:

OnPropertyChanged("Name");

UpdateSourceTrigger is for binding with the source property i.e normal .net property so to it requires to set on options like property change with mode twoway for dynamic change ex.text of textbox being change and the which updtaes a label to change. Where as if you want the change event to fire at the end i.e lost focus or click use explicit option with updatesourcetrigger.