WPF Textbox Binding Is Not Updating When Setting Value

Question

I have a small program to test out textbox databinding and it works when I change the value in the textbox itself, but when I try to change the value from the code-behind, the variable is updated but the Textbox is not updated. I have looked around but have not been able to find a solution, as most I have seen are for the textbox updating the variable, which is opposite of what I need. Here is the code:

XAML:

<Grid>
    <TextBox Text="{Binding FirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Height="23" Margin="127,37,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
    <TextBox Text="{Binding LastName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Height="23" Margin="127,88,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
    <TextBlock HorizontalAlignment="Left" Margin="28,40,0,0" TextWrapping="Wrap" Text="First Name" VerticalAlignment="Top"/>
    <TextBlock HorizontalAlignment="Left" Margin="28,91,0,0" TextWrapping="Wrap" Text="Last Name" VerticalAlignment="Top"/>
    <Button x:Name="Name" Content="Name!" HorizontalAlignment="Left" Margin="145,212,0,0" VerticalAlignment="Top" Width="75" Click="Name_Click"/>

</Grid>

And My Code:

namespace WpfApplication1
{
public class UIControls : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private string _firstName;
    private string _lastName;

    protected void Notify(string propertyName)
    {
        if(this.PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public string FirstName
    {
        get { return _firstName; }
        set
        {
            if (value != _firstName)
            {
                _firstName = value;
                Notify("FirstName");
            }

        }
    }
    public string LastName
    {
        get { return _lastName; }
        set
        {
            if (value != _lastName)
            {
                _lastName = value;
                Notify("LastName");
            }
        }
    }
}

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        UIControls viewModel = new UIControls();
        this.DataContext = viewModel;
    }

    private void Name_Click(object sender, RoutedEventArgs e)
    {
        UIControls ui = new UIControls();
        ui.FirstName = "Mike";
        ui.LastName = "Smith";
    }
}

}

Answer 1

Well you are creating new UIControls on every button click. New UIControls is not binded to text box. Try to create private filed that is binded to MainWindow, something like this:

public partial class MainWindow : Window
{

    private UIControls viewModel;
    public MainWindow()
    {
        InitializeComponent();
        viewModel = new UIControls();
        this.DataContext = viewModel;
    }

    private void Name_Click(object sender, RoutedEventArgs e)
    {
        viewModel.FirstName = "Mike";
        viewModel.LastName = "Smith";
    }