WPF data binding to a data model as an application resource - wpf

Question

I have have a problem with data binding. I have defined a application resource in XAML like this:
<Application.Resources>
<local:DataModel x:Key="myDataModel"/>
</Application.Resources>
I bound that model to a list, like this:
<ListView Name="ListBox"
ItemsSource="{Binding Source={StaticResource myDataModel}, Path=StatusList}"
HorizontalAlignment="Left"
HorizontalContentAlignment="Left"
VerticalContentAlignment="Top"
BorderThickness="0"
Background="#000000">
<ListView.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"></StackPanel>
</ItemsPanelTemplate>
</ListView.ItemsPanel>
<ListView.ItemTemplate>
<DataTemplate>
<Button MinWidth="20"
MinHeight="100"
Background="{Binding Converter={StaticResource StatusConverter}}"
Content="{Binding}" />
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
the problem now is that if I change the values of the application resource after binding, the list is not updated. It seems like the binding is done using a copy instead of a reference. The data of the model is updated fine, the PropertyChanged event is raised but the data inside the list never changes.
For your understanding: I have a network client who receives new data every 10 seconds that data needs to be drawn in that list. Right now whenever I receive data, I update the application resource, which as I said should be bound to the list. When I debug the code stopping right in front of the InitializeComponent() method of the XAML file containing the list and wait for a few seconds, I get the latest results of the data transferred, but thats it, it is never updated again.
Can you tell me a better way of defining a globally available instance of my model or a better way of binding it? As you see I need it in more than one part of my program.

Answer 1

public class DataModel
{
private IObservableCollection<short> this.statusList;
public IObservableCollection<short> StatusList
{
get {
return this.statusList;
}
set {
this.statusList = value;
this.RaisePropertyChanged("StatusList");
}
}
}
now you can do this one
this.StatusList = new ObservableCollection<short>();
hope this helps
EDIT
Here is an example that I am running without any problems.
<Window x:Class="WpfStackOverflowSpielWiese.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfStackOverflowSpielWiese"
Title="Window1"
Height="300"
Width="300">
<Window.Resources>
<local:DataModel x:Key="myDataModel" />
<local:StatusConverter x:Key="StatusConverter" />
</Window.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition />
</Grid.RowDefinitions>
<Button Grid.Row="0"
Content="Update"
Click="Button_Click" />
<ListView Name="ListBox"
Grid.Row="1"
ItemsSource="{Binding Source={StaticResource myDataModel}, Path=StatusList}"
HorizontalAlignment="Left"
HorizontalContentAlignment="Left"
VerticalContentAlignment="Top"
BorderThickness="0"
Background="#000000">
<ListView.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"></StackPanel>
</ItemsPanelTemplate>
</ListView.ItemsPanel>
<ListView.ItemTemplate>
<DataTemplate>
<Button MinWidth="20"
MinHeight="100"
Background="{Binding Converter={StaticResource StatusConverter}}"
Content="{Binding}"></Button>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</Grid>
</Window>
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Globalization;
using System.Windows;
using System.Windows.Data;
using System.Windows.Media;
namespace WpfStackOverflowSpielWiese
{
/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window
{
public Window1() {
this.InitializeComponent();
}
private void Button_Click(object sender, RoutedEventArgs e) {
var dataModel = this.TryFindResource("myDataModel") as DataModel;
if (dataModel != null) {
dataModel.UpdateStatusList(new[] {(short)1, (short)2, (short)3});
}
}
}
public class DataModel : INotifyPropertyChanged
{
private ObservableCollection<short> statusList;
public DataModel() {
this.StatusList = new ObservableCollection<short>();
this.UpdateStatusList(new[] {(short)1, (short)2, (short)3});
}
public void UpdateStatusList(IEnumerable<short> itemsToUpdate) {
foreach (var s in itemsToUpdate) {
this.StatusList.Add(s);
}
}
public ObservableCollection<short> StatusList {
get { return this.statusList; }
set {
this.statusList = value;
this.RaisePropertyChanged("StatusList");
}
}
private void RaisePropertyChanged(string propertyName) {
var eh = this.PropertyChanged;
if (eh != null) {
eh(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
public class StatusConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
if (value is short) {
switch ((short)value) {
case 1:
return Brushes.Red;
case 2:
return Brushes.Orange;
case 3:
return Brushes.Green;
}
}
return Brushes.White;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
return DependencyProperty.UnsetValue;
}
}
}

Answer 2

I have solved the problem. I have altered the values inside the list. But what I needed to do was create a new one and add the new values. All I needed to do was add this line:
this.StatusList = new IObservableCollection<short>()
and instead of doing it like this:
for(int i=0; i<ListSize; i++)
StatusList[i] = i;
i had to do:
for(int i=0; i<ListSize; i++)
StatusList.add( i );
You also need a little workaround from here: ListBoxItem produces "System.Windows.Data Error: 4" binding error
The surronding element needs to set the alignment properties using styles like this:
<Style TargetType="{x:Type ListBoxItem}">
<Setter Property="HorizontalContentAlignment" Value="Left" />
<Setter Property="VerticalContentAlignment" Value="Top" />
</Style>
This way you can avoid the System.Windows.Data Error 4 exceptions
again thanks to everyone who answered! :)