WPF Binding problem

Question

I have a textbox which I need to bind a string to.

<TextBox Name="txtDoc" Margin="5" Text ="{Binding Source={x:Static local:DocumentViewModel.FileText}, Path=FileText}">

The FileText property is changed on a different class:

DocumentViewModel.GetInstance().FileText = File.ReadAllText(document.Path);

The DocumentViewModel is a class with Singleton:

public class DocumentViewModel : INotifyPropertyChanged
{
    private static string fileText;

    public string FileText
    {
        get { return fileText; }
        set
        {
            fileText = value; // Call OnPropertyChanged whenever the property is updated
            OnPropertyChanged("FileText");
        }
    }

   private void OnPropertyChanged(string filetext)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(filetext));
        }
    }


    public event PropertyChangedEventHandler PropertyChanged = delegate { };

    private static DocumentViewModel instance = new DocumentViewModel();

    private DocumentViewModel() { }

    public static DocumentViewModel GetInstance()
    {
        return instance;
    }
}

I need to be able to change the value of the FileText property and reflect this change in the textbox. It's not working. I tried using TextBox as a static property but then the Onp

Ben · Accepted Answer · 2011-05-29 10:43:54Z

2

Try to set the source to your viewmodel instead of the property itself, and set the instance property to public? {Binding Source={x:Static local:DocumentViewModel.instance}, Path=FileText}

Edit: Included a complete example, that working for me:

Xaml:

<Window x:Class="Test.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:Test"
    Title="MainWindow" Height="350" Width="525"
    Loaded="Window_Loaded">
  <TextBox Name="txtDoc" Margin="5"
           Text="{Binding Source={x:Static local:DocumentViewModel.Instance}, Path=FileText}" />
</Window>

Code-behind:

public partial class MainWindow : Window
{
  public MainWindow()
  {
    InitializeComponent();
  }

  private void Window_Loaded(object sender, RoutedEventArgs e)
  {
    DocumentViewModel.Instance.FileText = "Hello world!";      
  }
}

public class DocumentViewModel : INotifyPropertyChanged
{
  #region Singleton implementation

  // Static constructor to create the singleton instance.
  static DocumentViewModel()
  {
    DocumentViewModel.Instance = new DocumentViewModel();
  }

  public static DocumentViewModel Instance { get; private set; }

  #endregion

  private static string fileText;
  public string FileText
  {
    get { return fileText; }
    set
    {
      if (fileText != value)
      {
        fileText = value;
        OnPropertyChanged("FileText");
      }
    }
  }

  #region INotifyPropertyChanged

  private void OnPropertyChanged(string filetext)
  {
    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler != null)
    {
      handler(this, new PropertyChangedEventArgs(filetext));
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;

  #endregion
}

edited May 29, 2011 at 10:43

answered May 29, 2011 at 9:31

Ben

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6 Comments

Gil Over a year ago

"I get an error: 'local:DocumentViewModel' member is not valid because it does not have a qualifying type name.

brunnerh Over a year ago

@Gil: The instance needs to be exposed as a public property, right now it's a private field.

Gil Over a year ago

Not working... I get no errors but the textbox doesn't show the text.

Gil Over a year ago

I tried testing the binding: I assigned a string value directly to the FileText : FileText = "Gil" and it did appear on the text box. Then I tried assigning the FileText property from another class: DocumentViewModel.FileText = "Gil"; this one didn't change the textbox. so the problem is not with the binding, it's with teh updating.

Ben Over a year ago

@Gil Included a complete example, that working for me. I changed your class to my taste, but the essence is the same.

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