PropertyChanged event always null

user_169058 0
Viewed 70294

I have the following (abbreviated) xaml:

<TextBlock Text="{Binding Path=statusMsg, UpdateSourceTrigger=PropertyChanged}"/>

I have a singleton class:

public class StatusMessage : INotifyPropertyChanged
{   
    private static StatusMessage instance = new StatusMessage();

    private StatusMessage() { }

    public static StatusMessage GetInstance()
    {
        return instance;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string status)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(status));
        }
    }

    private string statusMessage;
    public string statusMsg
    {
        get
        {
            return statusMessage;
        }
        set
        {
            statusMessage = value;
            OnPropertyChanged("statusMsg");
        }
    }
}

And in my main window constructor:

StatusMessage testMessage = StatusMessage.GetInstance();
testMessage.statusMsg = "This is a test msg";

I cannot get the textblock to display the test message. When I monitor the code through debug, the PropertyChanged is always null. Any ideas?

inotifypropertychanged binding wpf .net c#
11 Answers

Just in case: I had a similar problem but my mistake was that class which implemented INotifyPropertyChanged was private. Making it public resolved my case.

user_17924340

in my case this make it to work:

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;    // this row fixed everything
    }
    ****
    Some code here with properties etc
    ***
}
user_78539360

To complete the story, I also find if the bound property is static and the PropertyChanged event is not static, it will be null. A simple fix is to declare another static event so you have both as below:

public event PropertyChangedEventHandler PropertyChanged;
public static event PropertyChangedEventHandler StaticPropertyChanged;

Call PropertyChanged?.Invoke() or StaticPropertyChanged?.Invoke() according to whether the target property is static.

user_36520730

I had a similar issue, neither solutions above helped me. All I needed to do was to use the built c# Propertychanged. Beforehand I have implemented propertyChanged (by an accident) and it pointed at nothing.

user_105717970

If you follow all instructions, verifying your property name is correct, that it is correctly being assigned a new value, you are using a singleton to guarantee one instance of you view model, and you have successfully assigned your DataContext in the UI - make sure that whatever is forcing your property to update is done after the visual tree has been completed, i.e. move the refresh of your property to a button, rather than say the Loaded event of your window. I say this because I had the same issue, and found that when I refreshed my view model data property from my Infragistics NetAdvantage ribbon window's Loaded event, my PropertyChanged event was always null.

jadusty_618400
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