WPF MVVM and Observablecollect - wpf

Question

I have a wpf application and I want to update my listview when I change the value through the UI using Observablecollect. But I don't get what I expect. When I change the value I won't update my list view.
View Code(Xaml)
<UserControl x:Class="DataWatch.View.CompareData"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:ViewModels="clr-namespace:DataWatch.ViewModel"
mc:Ignorable="d"
d:DesignHeight="340" d:DesignWidth="600">
<UserControl.DataContext>
<ViewModels:CompareViewModel/>
</UserControl.DataContext>
<Grid>
<ListView HorizontalAlignment="Left" Name="comparelistview" VerticalAlignment="Top" Width="600" Height="340" ItemsSource="{Binding DisplayData}">
<ListView.View>
<GridView>
<GridViewColumn Width="150" Header="Key"
DisplayMemberBinding="{Binding Path=Key}" />
<GridViewColumn Width="150" Header="Project Data"
DisplayMemberBinding="{Binding Path=ProjectData}" />
<GridViewColumn Width="150" Header="Import Data"
DisplayMemberBinding="{Binding Path=ImportData}"/>
<GridViewColumn Width="150" Header="State"
DisplayMemberBinding="{Binding Path=State}"/>
</GridView>
</ListView.View>
</ListView>
</Grid>
ViewModel
namespace DataWatch.ViewModel
{
public class CompareViewModel
{
private ObservableCollection<CompareDiplayData> _displayData;
public CompareViewModel()
{
_displayData = new ObservableCollection<CompareDiplayData>();
}
public ObservableCollection<CompareDiplayData> DisplayData
{
get { return _displayData; }
}
}
Model:
namespace DataWatch.Model
{
public class CompareDiplayData : INotifyPropertyChanged
{
private string _key;
public string Key
{
set
{
_key = value;
this.Changed("Key");
}
get
{
return _key;
}
}
private string _projectData;
public string ProjectData
{
set
{
_projectData = value;
this.Changed("ProjectData");
}
get
{
return _projectData;
}
}
private string _importData;
public string ImportData
{
set
{
_importData = value;
this.Changed("ImportData");
}
get
{
return _importData;
}
}
private string _state;
public string State
{
set
{
_state = value;
this.Changed("State");
}
get
{
return _state;
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void Changed(string PropertyName)
{
if (this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
}
}
}
When I change the value in displayData ,but Listview won't update the data.
combobox view control
<UserControl x:Class="DataWatch.View.SelectPanel"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:ViewModels="clr-namespace:DataWatch.ViewModel"
xmlns:AttachProperty="clr-namespace:DataWatch.AttachedProperty"
mc:Ignorable="d"
d:DesignHeight="30" d:DesignWidth="600">
<UserControl.DataContext>
<ViewModels:CompareViewModel/>
</UserControl.DataContext>
<Grid Name="good">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="150">
</ColumnDefinition>
<ColumnDefinition Width="300">
</ColumnDefinition>
<ColumnDefinition Width="150">
</ColumnDefinition>
</Grid.ColumnDefinitions>
<ComboBox Height="23" HorizontalAlignment="Left" Grid.Column="0" Grid.Row="0" Margin="15,4,6,4" x:Name="KeyComboBox" VerticalAlignment="Top" Width="120" Text="Choose Key" AttachProperty:SelectionBehavior.SelectionChanged="{Binding SelectKeyCmd}" SelectedItem="{Binding SelectedKey, Mode=TwoWay}" ItemsSource="{Binding KeyComboboxItem}"
IsEditable="true" IsReadOnly="true"
IsDropDownOpen="True" StaysOpenOnEdit="True"/>
<ComboBox Height="23" HorizontalAlignment="Left" Grid.Column="1" Grid.Row="0" Margin="90,4,6,4" Name="compareitemcomBox" VerticalAlignment="Top" Width="120" Text="Compare Item" AttachProperty:SelectionBehavior.SelectionChanged="{Binding SelectKeyCmd}" SelectedItem="{Binding SelectedComparedData, Mode=TwoWay}" ItemsSource="{Binding CompareComboboxItem}"
IsEditable="true" IsReadOnly="true"
IsDropDownOpen="True" StaysOpenOnEdit="True"/>
<ComboBox Height="23" HorizontalAlignment="Left" Grid.Column="2" Grid.Row="0" Margin="15,4,6,4" Name="display" VerticalAlignment="Top" Width="120" Text="Choose State"
IsEditable="true" IsReadOnly="true"
IsDropDownOpen="True" StaysOpenOnEdit="True"/>
</Grid>
Attach property
public class SelectionBehavior
{
public static DependencyProperty SelectionChangedProperty =
DependencyProperty.RegisterAttached("SelectionChanged",
typeof(ICommand),
typeof(SelectionBehavior),
new UIPropertyMetadata(SelectionBehavior.SelectedItemChanged));
public static void SetSelectionChanged(DependencyObject target, ICommand value)
{
target.SetValue(SelectionBehavior.SelectionChangedProperty, value);
}
private static void SelectedItemChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
{
Selector element = target as Selector;
if (element == null) throw new InvalidOperationException("This behavior can be attached to Selector item only.");
if ((e.NewValue != null) && (e.OldValue == null))
{
element.SelectionChanged += SelectionChanged;
}
else if ((e.NewValue == null) && (e.OldValue != null))
{
element.SelectionChanged -= SelectionChanged;
}
}
private static void SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
{
UIElement element = (UIElement)sender;
ICommand command = (ICommand)element.GetValue(SelectionBehavior.SelectionChangedProperty);
command.Execute(((Selector)sender).SelectedValue);
}
}
viewmodel
public class CompareViewModel
{
private readonly ICommand _selectKeyCmd;
private List<string> _pro_Property;
private List<string> _imp_Property;
private string selectedKey;
private ObservableCollection<string> compareComboboxItem;
private DataTable _dt;
private CompareDiplayData domObject;
private ObservableCollection<CompareDiplayData> _displayData;
public CompareViewModel()
{
_displayData = new ObservableCollection<CompareDiplayData>();
_selectKeyCmd = new RelayCommand(ComboboxChanged, ComboboxIsChanged);
}
private void ReslutData()
{_displayData =null;
if (SelectedKey != null && SelectedComparedData != null)
{
foreach (DataRow pdr in _projectDt.Rows)
{
CompareDiplayData cdd = new CompareDiplayData();
foreach (DataRow idr in _importDt.Rows)
{
if (pdr[SelectedKey].ToString() == idr[SelectedKey].ToString())
{
cdd.Key = pdr[SelectedKey].ToString();
cdd.ProjectData = pdr[SelectedComparedData].ToString();
cdd.ImportData = idr[SelectedComparedData].ToString();
if (pdr[SelectedComparedData].ToString() == idr[SelectedComparedData].ToString())
cdd.State = "Match";
else
cdd.State = "Mismatch";
_displayData.Add(cdd);
}
}
}
}
}
public ObservableCollection<CompareDiplayData> DisplayData
{
get { return _displayData; }
}
public ICommand SelectKeyCmd
{
get { return _selectKeyCmd; }
}
private void ComboboxChanged(object obj)
{
ReslutData();
}
private bool ComboboxIsChanged(object obj)
{
return true;
}`}`

Answer 1

You are updating the reference of the Observablecollection here so that needs to be notified as the PropertyChange. In order to fix this, you will have to implement the INotifyPropertyChanged on your ViewModel also and write the setter of the DisplayData and raise property change for it.
public ObservableCollection<CompareDiplayData> DisplayData
{
get { return _displayData; }
set{_displayData = value;
this.Changed("DisplayData");
}
and in your ReslutData functin instead of update the variable _displayData, update the Property DisplayData.