Question

I can’t figure out why the binding changes in my large project wont work. I have simplified it down to a sample project that still doesn’t work. I would like to continue to set the datacontext the way I currently am if possible because that is how the other project does it. With the following code the text in SomeText is not showing up in the textbox. How do I fix this?

Code Behind:

public partial class MainPage : UserControl
{
    public MainPage()
    {
        InitializeComponent();
        DataContext = new ViewModel();
    }
}

Data Class:

public class ViewModel
{
    public string SomeText = "This is some text.";
}

Main User Control:

  <UserControl xmlns:ig="http://schemas.infragistics.com/xaml"          x:Class="XamGridVisibilityBindingTest.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:XamGridVisibilityBindingTest="clr-namespace:XamGridVisibilityBindingTest" mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White">
        <TextBox Text="{Binding SomeText}" BorderBrush="#FFE80F0F" Width="100" Height="50">    </TextBox>
    </Grid>
</UserControl>

Edit: I am only trying to do one-way binding.

Answer 1

You need to use a property, and make your VM inherit from INotifyPropertyChanged and raise the PropertyChanged event whenever SomeText changes:

public class ViewModel : INotifyPropertyChanged
{
    private string someText;

    public event PropertyChangedEventHandler PropertyChanged;

    public string SomeText 
    {
        get { return someText; }
        set 
        { 
            someText = value; 
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs("SomeText"));
            }
        }
    }

    public ViewModel()
    {
        SomeText = "This is some text.";
    }
}