Question

I am trying to make ListBox which updates its content according to some changing data.
The XAML is as follows

StackPanel Orientation="Vertical">
<ListBox  x:Name="listWatch"  >
    <ListBox.ItemTemplate>
        <DataTemplate>
            <Grid ShowGridLines="True">
                <Grid Grid.Column="0" Background="{Binding Path=Color">
                    <TextBlock  Text="{ Binding Path=LTP}"  Padding="2 2 2 2"/>
                </Grid>
            </Grid>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>
<Button x:Name="btn"  Click="btn_Click" Content="Button" />

The class i used for form data strucure is as follows

 public class WatchRow : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    string _color;
    decimal _lTP;

    public WatchRow(decimal LTP,string color)
    {         
        this.LTP = LTP;          
        this.Color = color;
    }
    public string Color 
    {
        get { return _color; }
        set{
            _color = value;
            OnPropertyChanged(_color);
        }
    }       
    public decimal LTP
    {
        get { return _lTP; }
        set
        {
            _lTP = value;
            OnPropertyChanged(_lTP.ToString());
        }
    }  
    protected void OnPropertyChanged(string info)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(info));
        }
    }
}

 public class Watch:ObservableCollection<WatchRow>
    {
        public Watch():base()
        {
        }       
    }

And the code behind file is like

    Watch watch = new Watch();
private void PhoneApplicationPage_Loaded_1(object sender, RoutedEventArgs e)
{
    watch.Add(new WatchRow(132, "black"));
    watch.Add(new WatchRow(123, "red"));
    listWatch.ItemsSource = watch;  
watch[0].Color = "green";
}

private void btn_Click(object sender, RoutedEventArgs e)
{

    watch[0].Color = "green";
}

My problem is that i am not able to change the color of the list box item by setting the color property(watch[0].Color = “green”;) in btn_Click as shown in the code. But the same code works in PhoneApplicationPage_Loaded_1. I don’t know what i’m wrong. Any Ideas?

Answer 1

I believe the problem is a slight change to how you are using PropertyChanged. When you are calling OnPropertyChanged, pass through the name of the property that you are changing, rather than the value. For example:

public string Color 
    {
        get { return _color; }
        set{
            _color = value;
            OnPropertyChanged(_color);
        }
    }   

Should be:

public string Color 
    {
        get { return _color; }
        set{
            _color = value;
            OnPropertyChanged("Color");
        }
    }   

Also, I’m not sure if this is necessarily a problem, but this is how I’ve always created the OnPropertyChanged function:

Instead of:

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

Try:

private void OnPropertyChanged(String info)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(info));
            }
        }

Also, as Magnus Johansson mentioned, define a brush, and bind the Color, rather than a string. So the Color property would be (see his explanation for further details on this):

private Color _color;
public Color Color 
        {
            get { return _color; }
            set{
                _color = value;
                OnPropertyChanged("Color");
            }
        }