Simple Binding of Data from code behind to XAML

Question

Hi,
I am new to WPF concepts. I want to just display a string in a textbox. I tried the following C# code and XAML to bind a string to a TextBox.Text property. C# code:

public partial class Window1 : Window
{
    public int TmpVal;
    public string TmpStr;

     public Window1()
    {
        TmpVal = 50;
        TmpStr = "Windows Created";
        InitializeComponent();
        this.DataContext = this;
    }
    private void viewButton_Click(object sender, RoutedEventArgs args)
    {
        TmpStr = "Button clicked";
    }
}

}

XAML:

 <Window x:Class="TestWPF.Window1"
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="600" Width="800" x:Name="ThisWindow">
<Grid>
    <TextBox Name="txtTest1" Margin="200,0,200,200" HorizontalAlignment="Left" Height="50" Width="200" Text="{Binding TmpStr, ElementName=ThisWindow}" />
    <Button Name="butTest1"  Click="viewButton_Click">Test123</Button>
</Grid>
</Window>

On execution I always get blank text in my textbox (even when I invoke the click event).
I browsed through the stackoverflow site but couldn't solve the problem (though many questions were close to this one)
Can someone suggest me if anything is overlooked or missed out?

Answer 1

Databinding does not work with fields. Use Properties instead:

public int TmpVal {get; set;}
public string TmpStr {get; set;}

Also if you want the textbox to automatically pick up changes from your data you would ideally need to implement INotifyPropertyChanged or make it a dependency property or have a XXXChanged event for each XXX property (this doesn't work anymore).

<Window x:Class="WpfApplication5.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" x:Name="ThisWindow">
    <StackPanel>
        <TextBox Name="txtTest1" Text="{Binding TmpStr, ElementName=ThisWindow}" />
        <Button Name="butTest1"  Click="viewButton_Click">Test123</Button>
    </StackPanel>
</Window>

And the code behind:

public partial class Window1 : Window, INotifyPropertyChanged
{
 public Window1()
 {
  this.TmpStr = "Windows Created";
  this.InitializeComponent();
  this.DataContext = this;
 }

 public event PropertyChangedEventHandler PropertyChanged;

 public string TmpStr { get; set; }

 public int TmpVal { get; set; }

 private void viewButton_Click(object sender, RoutedEventArgs args)
 {
  this.TmpStr = "Button clicked";
  if (this.PropertyChanged != null)
  {
   this.PropertyChanged(this, new PropertyChangedEventArgs("TmpStr"));
  }
 }
}