In my C# XAML Windows 8.1 app, how do I make programmatic binding work?

Question

I'm new to Windows 8.1 development, as well as C# and XAML, so forgive me if this is a terribly rudimentary question. First, I used the following page as the inspiration for much of what I've done here:

https://msdn.microsoft.com/en-us/library/ms742863(v=vs.110).aspx

Here's the XAML of my page:

<StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Button HorizontalAlignment="Left" Content="this is my button"  Click="Button_Click" />
    <TextBox Text="This is a bound text box" x:Name="BoundTextBox" />
    <TextBlock Text="This is a bound text block" x:Name="BoundTextBlock" />
</StackPanel>

And here's my code-behind:

public sealed partial class MyPage : Page, INotifyPropertyChanged
    {

        #region Str variable
        // Create the source string.
        private string str = "Initial Value of the 'str' variable";

        public string Str
        {
            get { return str; }
            set { 
                str = value;
                NotifyPropertyChanged("Str");
            }
        }


        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }       
        #endregion

        ...

        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            // Create the binding description.
            Binding binding = new Binding(); // 'Binding' has no one-parameter constructors, so changed from MS's documentation
            binding.Mode = BindingMode.OneWay; // I tried TwoWay, as well, but that also did not work
            binding.Source = Str; 

            // Attach the binding to the target.
            BoundTextBox.SetBinding(TextBox.TextProperty, binding);
            BoundTextBlock.SetBinding(TextBlock.TextProperty, binding);
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            this.TextColorBrush = new SolidColorBrush(Colors.Red);

            if (Str == "Changed Value ONE")
            {
                Str = "SECOND Changed Value";
            }
            else
            {
                Str = "Changed Value ONE";
            }
        }
    }

What's happening is that the TextBox and TextBlock both get their Text property set to Initial Value of the 'str' variable, but when I click the button and the underlying value of str changes (which I verified is actually happening with breakpoints and step-through), the Text values of the TextBlock and TextBox do not change.

When I do the binding another way (i.e. in the XAML rather than in the code-behind), it does work. Here's all I did to make that happen:

    <Page
        x:Name="This"
        ...
    >
        <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
            <Button HorizontalAlignment="Left" Content="this is my button"  Click="Button_Click" />
            <TextBox Text="{Binding ElementName=This, Path=Str, Mode=OneWay}" x:Name="BoundTextBox" />
            <TextBlock Text="{Binding ElementName=This, Path=Str, Mode=OneWay}" x:Name="BoundTextBlock" />
        </StackPanel>
    </Page>

So my main question is "How can I get the code-behind data binding to work, like the XAML-based binding works?".

Thanks in advance for any help, advice, or tips you can offer!

nhabuiduc nhabuiduc · Accepted Answer · 2015-04-13T19:31:11

You should set binding.Source = this; binding.Path = new PropertyPath("Str")

The reason is if you set binding.Source = Str , it only gets value of Str, and no way to detect change.Therefore the source should be class implementing INotifyPropertyChanged and also give it a Path in order to Binding class observeres the changes of that propery

In my C# XAML Windows 8.1 app, how do I make programmatic binding work?

1 Answers