wpf - mvvm - listbox - IsEnabled

Question

Hi
I have a listbox which I want to set its property IsEnabled while clicking on button. 
I tried to bind the button command  to a method on the ViewModel which supposed to changh a boolean parameter to TRUE \ FALSE, and the listbox is bind to a property which get and set this parameter. it doesnt work.

here is my code:
in xaml:
<Button Canvas.Left="743.213" Canvas.Top="58" Height="114" Width="113.625" Template="{DynamicResource ButtonControlTemplate2}" Command="{Binding NewListRecord}" >make list </Button> 

<ListBox ScrollViewer.VerticalScrollBarVisibility="Disabled" FontFamily="Ariel" Foreground="OrangeRed" Margin="0.5,0,1,0" Grid.Column="1" IsEnabled="{Binding isProductListEnabled}"></ListBox>

ViewModel:

private

 

bool productListEnabledDisabled;

 

public ICommand NewListRecord
{
      get
      {
           if (newListRecord == null)
          {
                  newListRecord = new DelegateCommand(RecordNewList);
          }
          return newListRecord;
     }
}

 

private void RecordNewList()
{
     this.isProductListEnabled = true;
}

public

 

bool isProductListEnabled
{
       get { return productListEnabledDisabled; }
       set { this.productListEnabledDisabled = value;}
}



can anyone help me with this?

Answer 1

Hi Yehuda,

to make this work, you'll have to notify the View that the isProductListEnabled property has changed. To do so, implement INotifyPropertyChanged in your ViewModel. Here's a sample that shows how to work this out; I didn't follow MVVM here for the sake of simplicity:

<Window x:Class="WpfTests.ListBoxIsEnabled"
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   Title="ListBoxIsEnabled" Height="300" Width="300"
   DataContext="{Binding RelativeSource={RelativeSource Self}}"
   >

   <Grid>
      <Grid.RowDefinitions>
         <RowDefinition Height="Auto"/>
         <RowDefinition Height="*"/>
         <RowDefinition Height="Auto"/>
      </Grid.RowDefinitions>
      <Button Grid.Row="0" Content="Toggle ListBox'es IsEnabled-prop" Click="Button_Click" Margin="5" Padding="5"/>
      <ListBox Grid.Row="1" Foreground="OrangeRed" IsEnabled="{Binding IsListBoxEnabled}" Margin="5" SelectedIndex="0">
         <ListBoxItem Content="Item1"/>
         <ListBoxItem Content="Item2"/>
      </ListBox>
      <CheckBox Grid.Row="2" Content="ListBox is enabled" IsChecked="{Binding IsListBoxEnabled}" Margin="5"/>
   </Grid>
</Window>

And the code-behind:

using System;
using System.Collections.Generic;
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;
using System.ComponentModel;

namespace WpfTests
{
   /// <summary>
   /// Interaction logic for ListBoxIsEnabled.xaml
   /// </summary>
   public partial class ListBoxIsEnabled : Window, INotifyPropertyChanged
   {

      private bool _fIsListBoxEnabled = true;
      public bool IsListBoxEnabled
      {
         get { return _fIsListBoxEnabled; }
         set
         {
            _fIsListBoxEnabled = value;
            OnPropertyChanged("IsListBoxEnabled");
         }
      }

      private void Button_Click(object sender, RoutedEventArgs e)
      {
         IsListBoxEnabled = !IsListBoxEnabled;
      }

      public ListBoxIsEnabled()
      {
         InitializeComponent();
      }


      #region INotifyPropertyChanged Members

      public event PropertyChangedEventHandler PropertyChanged;
      private void OnPropertyChanged(string prop)
      {
         if (PropertyChanged != null)
         {
            PropertyChanged(this, new PropertyChangedEventArgs(prop));
         }
      }

      #endregion

   }
}

---

Cheers,
Olaf

Answer 2

Olaf
Thank you very much
It's working!

Apparently I was only missing this line:
OnPropertyChanged("IsListBoxEnabled");
 (in the 'set' of  IsListBoxEnabled property...)

b.t.w. just for general knowledge,
could I use for the same scenario with DependencyProperty?

Again,
Thanks - Yehuda

Answer 3

Hi Yehuda,

yes, that'd be an alternative approach. Just replace the code-behind of my previous sample with this one here:

using System;
using System.Collections.Generic;
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 WpfTests
{
   /// <summary>
   /// Interaction logic for ListBoxIsEnabled.xaml
   /// </summary>
   public partial class ListBoxIsEnabled : Window
   {
      public static DependencyProperty IsListBoxEnabledProperty =
         DependencyProperty.Register(
               "IsListBoxEnabled",
               typeof(bool),
               typeof(ListBoxIsEnabled)
            );

      public bool IsListBoxEnabled
      {
         get { return (bool)GetValue(IsListBoxEnabledProperty); }
         set { SetValue(IsListBoxEnabledProperty, value); }
      }

      private void Button_Click(object sender, RoutedEventArgs e)
      {
         IsListBoxEnabled = !IsListBoxEnabled;
      }

      public ListBoxIsEnabled()
      {
         InitializeComponent();
      }
   }
}

---

Cheers,
Olaf