刷新属性上的ListView项已更改

Question

I have a listView like this :

<ListView Grid.Row="1" x:Name="itemsListView" 
          BorderBrush="White" HorizontalAlignment="Stretch"
          ItemsSource="{Binding Path=Items}"
          SelectedItem="{Binding Path=ActualItem}">
    <ListView.View>
        <GridView>
            <GridViewColumn Header="{x:Static p:Resources.STATUS}">
                <GridViewColumn.CellTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                            <local:StatusElement State="{Binding Path=Status,Mode=OneWay,UpdateSourceTrigger=PropertyChanged}"
                                                Height="20"/>
                        </StackPanel>
                    </DataTemplate>
                </GridViewColumn.CellTemplate>
            </GridViewColumn>

            <GridViewColumn Header="{x:Static p:Resources.NAME}"
                            DisplayMemberBinding="{Binding Path=Name,Mode=OneWay,UpdateSourceTrigger=PropertyChanged}"/>
        </GridView>
    </ListView.View>
</ListView>

It binds a list of items named Items with many fields. A thread parse the items and update the fields when it finishes. I call method OnPropertyChanged when fields are updated. It works fine for all fields except the one using my UserControl local:StatusElement . I've try to display my STATUS like the NAME, it's refreshes correctly but with local:StatusElement there is no refresh. breakpoints on get/set for StatusElement.State are never reached.

My userControl :

<UserControl ...
             x:Name="mainControl">
    <Grid Name="LabelGrid">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Image Grid.Column="0" Name="MyImage"
               Source="{Binding Source, Source={StaticResource MyImage}}"
               Width="{Binding Height, ElementName=mainControl}"
               Height="{Binding Height, ElementName=mainControl}"/>
        <Label Grid.Column="1" Name="statusLabel"/>
    </Grid>
</UserControl>

and:

public partial class StatusElement : UserControl
{

    // Dependency property backing variables
    public static readonly DependencyProperty StateProperty = DependencyProperty.Register("State",
                 typeof(String), typeof(StatusElement), new UIPropertyMetadata(null));

    private string _state = "";
    public String State
    {
        get
        {
            return _state;
        }
        set
        {
            _state = value;
            RefreshState();
        }
    }

    private void RefreshState()
    {
        switch (State)
        {
            case "":
                MyImage.Visibility = Visibility.Hidden;
                break;
            default:
                MyImage.Visibility = Visibility.Visible;
                break;
        }
        statusLabel.Content = State;
    }

    public StatusElement()
    {
        InitializeComponent();
        RefreshState();
    }
}

Why the Content of my statusLabel doesn't refresh ?

Answer 1

Your definition of the State dependency property is wrong.

It has to look like shown below, where the CLR property wrapper must call the GetValue and SetValue methods of the DependencyObject that owns the property.

public static readonly DependencyProperty StateProperty = DependencyProperty.Register(
     "State",
     typeof(string),
     typeof(StatusElement),
     new PropertyMetadata(null, (o, e) => ((StatusElement)o).RefreshState()));

public string State
{
    get { return (string)GetValue(StateProperty); }
    set { SetValue(StateProperty, value); }
}

Note the second argument to the PropertyMetadata constructor. It is a static PropertyChangedCallback , implemented as lambda expression.

Answer 2

Your class doesnt implement the INotifyPropertyChanged event. Implement it for the update to happen.

Notifies clients that a property value has changed.

public partial class StatusElement : UserControl,INotifyPropertyChanged
{
 ....

public event PropertyChangedEventHandler PropertyChanged;

private void RefreshState([CallerMemberName]string prop = "")
{
    switch (State)
    {
        case "":
            MyImage.Visibility = Visibility.Hidden;
            break;
        default:
            MyImage.Visibility = Visibility.Visible;
            break;
    }
    statusLabel.Content = State;
    if (PropertyChanged != null)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(prop));

    }
}
}