ICommand does not fire with button in ItemTemplate - mvvm-light

Question

I am currently doing a test with ICommand and I wonder why ICommand does not fire with button in ListBox.ItemTemplate. But when used outside the template, it works.
here's the window xaml
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication1" x:Class="WpfApplication1.Window2"
Title="Window2" Height="300" Width="300">
<Window.DataContext>
<local:W2VM/>
</Window.DataContext>
<Grid>
<ListBox x:Name="listHistory" BorderThickness="0" Margin="0" Padding="0" HorizontalContentAlignment="Stretch" ItemsSource="{Binding History}">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock Text="{Binding ''}" />
<Button
Grid.Column="1"
HorizontalAlignment="Right"
x:Uid="btnDeleteHistoryItem"
x:Name="btnDeleteHistoryItem"
Content="r"
FontFamily="Marlett"
Visibility="Hidden" Command="{Binding MeClick}"
/>
</Grid>
<DataTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Visibility" TargetName="btnDeleteHistoryItem" Value="Visible" />
</Trigger>
</DataTemplate.Triggers>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Button Content=" exit " VerticalAlignment="Bottom" Command="{Binding ExitCommand}" />
</Grid>
</Window>
here's the complete ViewModel code
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
namespace WpfApplication1
{
/// <summary>
/// Interaction logic for Window2.xaml
/// </summary>
public partial class Window2 : Window
{
public Window2()
{
InitializeComponent();
}
}
public class W2VM : ViewModelBase
{
public List<string> _History = new List<string>();
public List<string> History
{
get { return this._History; }
}
public ICommand MeClick
{
get;
internal set;
}
public ICommand ExitCommand
{
get;
internal set;
}
public W2VM()
{
this.History.AddRange(new string[] {
"jayson", "hello", "world"
});
this.MeClick = new RelayCommand(Test);
this.ExitCommand = new RelayCommand(Exit);
}
void Exit()
{
Application.Current.Shutdown();
}
void Test()
{
Debug.WriteLine("hello world");
MessageBox.Show("do something incredible");
}
}
}
Test() does not fire
ok I got it working..
<Window.Resources>
<me:W2VM x:Key="local" />
</Window.Resources>
instead of
<Window.DataContext>
<local:W2VM/>
</Window.DataContext>
and my window grid
<Grid DataContext="{StaticResource local}">
<ListBox x:Name="listHistory" BorderThickness="0" Margin="0" Padding="0" HorizontalContentAlignment="Stretch" ItemsSource="{Binding History}">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock Text="{Binding ''}" />
<Button
Grid.Column="1"
HorizontalAlignment="Right"
x:Uid="btnDeleteHistoryItem"
x:Name="btnDeleteHistoryItem"
Content="r"
FontFamily="Marlett"
Visibility="Hidden" Command="{Binding MeClick, Source={StaticResource local}}" />
</Grid>
<DataTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Visibility" TargetName="btnDeleteHistoryItem" Value="Visible" />
</Trigger>
</DataTemplate.Triggers>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Button Content=" exit " VerticalAlignment="Bottom" Command="{Binding ExitCommand}" />
</Grid>
now this will raise another question.
How would I know which ListViewItem was clicked when the btnDeleteHistoryItem command was just routed?

Answer 1

Are you using the relaycommand of mvvm-light?
I use command parameters to pass information to the command method:
<Button
Grid.Column="1"
HorizontalAlignment="Right"
x:Uid="btnDeleteHistoryItem"
x:Name="btnDeleteHistoryItem"
Content="r"
FontFamily="Marlett"
Visibility="Hidden" Command="{Binding MeClick, Source=StaticResource local}}"
CommandParameter="YourUniqueIdentifyingVariable" />
and then in your view model:
public RelayCommand<string> MeClick{
get { return _MyClick; }
private set { _MyClick = value; }
}
public New()
{
MeClick = new RelayCommand<string>(MySub, MySubIsEnabled);
}
private void MySub(string sParam)
{
//do stuff here, YourUniqueIdentifyingVariable is sParam
}
private bool MySubIsEnabled(string sParam)
{
return true;
}
you can bind "YourUniqueIdentifyingVariable" to the ID of the record or some other value that you can process in your command method
Code is untested but should work