INotifyPropertyChanged的PropertyChanged成员始终为null

Question

I'm trying to bind a text block to my variable slctItem . I can see it contain the necessary data I need however my window does not show the data I'm expecting. Here is the code behind for my control. This control is used by a pop up window which will display the values of the control.

When walking the code I see that handler returns null every time in the OnPropertyChanged() method. Why? I must be doing something wrong here. Again slcItem does contain the data I'm wanting to use. The OnPropertyChanged() method also fires it just contains null for handler.

public partial class MetaData : UserControl, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private string _slctItem;

    public MetaData()
    {
        InitializeComponent();
    }

    public string slctItem
    {
        get
        {
            return _slctItem;
        }
        set
        {
            _slctItem = value;
            OnPropertyChanged("slctItem");
        }
    }

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

    internal void Refresh()
    {
        try
        {
            // If DataContext is Null or a detached DataRow, disable the view
            if (DataContext != null && (DataContext is DataRow && ((DataRow)DataContext).RowState != System.Data.DataRowState.Detached))
            {

                if (DataContext is "Something Here")
                {
                    slctItem = (("Something Here")this.DataContext).NAME;
                }
            }
        }
        catch (Exception e)
        {
            throw new Exception("MetaData -> Refresh(): " + e.Message);
        }
    }

Here is the XAML code for my control. Here I'm trying to bind to slctItem

<TextBox Grid.Column="2" Grid.Row="0" Text="{Binding Path=slctItem, Mode=OneWay, Converter={StaticResource myFirstCharToUpperConverter}}" Width="150" Height="25" HorizontalAlignment="Left" />

Answer 1

You need to set the DataContext to yourself:

public MetaData()
{
    InitializeComponent();
    this.DataContext = this;
}

This will allow the binding to find the appropriate property. Right now, if you look at the Debug Output in the Output Window at runtime, you should see binding errors since the data context is unset.