Dependency property not raising when value assinged in view model

Question

Hai

I am trying to create a custom datagrid control with a property called SelectedItem and I am trying to assign some object to this property in my viewmodel.
My codes are

Custom control

        public object SelectedItem
        {
            get => GetValue(selecteditemProperty);
            set => SetValue(selecteditemProperty, value);
        }
        public static readonly DependencyProperty selecteditemProperty = DependencyProperty.Register("SelectedItem", typeof(object), typeof(IGridListBoxColumn), new PropertyMetadata(new PropertyChangedCallback(SelectedItem_Changed)));
        private static void SelectedItem_Changed(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            IGridListBoxColumn mycontrol = sender as IGridListBoxColumn;
            mycontrol.callSelectedItem(e);
            MessageBox.Show("selected triggered");
            //not working
        }
        private void callSelectedItem(DependencyPropertyChangedEventArgs e)
        {
            MessageBox.Show("selected triggered");
        }

Mainwindow

private void Journal_Click(object sender, RoutedEventArgs e)
        {
            JournalViewModel Jvm = new JournalViewModel();
            Journal Jrn = new Journal();
            Jrn.DataContext = Jvm;
            MainFrame.Content = Jrn;
        }

Journal Page

    <Page.Resources>
        <CollectionViewSource x:Key="AcHeadList" Source="{Binding Tlb_Achead}"/>
    </Page.Resources>            

        <MyControls:IGrid.Columns>
                        <MyControls:IGridListBoxColumn Header="A/c Head" ItemsSource="{Binding Source={StaticResource AcHeadList}}" DisplayMember="Achead" SelectedItem ="{Binding **M_Tlb_Achead_Selected**, Mode=TwoWay}" Width="150"/>
                    </MyControls:IGrid.Columns>

viewmodel

Ob_JournalModel = new ObservableCollection<JournalModel>();

JournalModel Jm = new JournalModel();
Jm.**M_Tlb_Achead_Selected** = new ICMaster { Achead = value.M_Achead, CMaster_Id = value.M_CMaster_Id };

NotifyPropertyChanged("Ob_JournalModel");

Here When I assign value to M_Tlb_Achead_Selected I want to do some thing inside my dependency property.
please help me how to do this.

thanks

Answer 1

Hi, I copy your code in Window and Page and it works fine:

<Window x:Class="WpfApp1.Window40"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="Window40" Height="450" Width="800">
  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition Height="Auto"/>
      <RowDefinition Height="Auto"/>
      <RowDefinition/>
    </Grid.RowDefinitions>
    <Button Content="Show Journal" Click="Journal_Click"/>
    <Button Grid.Row="1" Content="Set item" Click="Button_Click" />
    <Frame Grid.Row="2" x:Name="MainFrame"/>
  </Grid>
</Window>

CodeBehind Main Window and ViewModel:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Windows;
using WpfApp40;

namespace WpfApp1
{
  /// <summary>
  /// Interaction logic for Window40.xaml
  /// </summary>
  public partial class Window40 : Window
  {
    public Window40()
    {
      InitializeComponent();
    }

    Window40Journal Jrn;

    private void Journal_Click(object sender, RoutedEventArgs e)
    {
      JournalViewModel Jvm = new JournalViewModel();
      Jrn = new Window40Journal();
      Jrn.DataContext = Jvm;
      MainFrame.Content = Jrn;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
      if (Jrn != null) Jrn.SelectedItem = "x";
    }
  }
}

namespace WpfApp40
{
  public class JournalViewModel
  {
    public JournalViewModel()
    {
      NameList = new ObservableCollection<MarKList>(db.MarKLists.ToList());
      Tlb_Achead = new ObservableCollection<Student>(db.StudentList.ToList());
    }
    Model db = new Model();
    public ObservableCollection<MarKList> NameList { get; set; }
    public ObservableCollection<Student> Tlb_Achead { get; set; }
  }
  public class Student
  {
    public string M_Name { get; set; }
    public int M_GenderID { get; set; }
    public string M_Mark1 { get; set; }
    public int M_Total { get; set; }
  }
  public class MarKList
  {
    public string Name { get; set; }
    public int ID { get; set; }
  }
  internal class Model
  {
    Random rnd = new Random();
    internal IEnumerable<MarKList> MarKLists
    {
      get
      {
        var l = new List<MarKList>();
        l.Add(new MarKList() { ID = 1, Name = "Male" });
        l.Add(new MarKList() { ID = 2, Name = "Female" });
        l.Add(new MarKList() { ID = 3, Name = "TransGender" });
        return l;
      }
    }
    internal IEnumerable<Student> StudentList { get { for (int i = 0; i < 10; i++) yield return new Student() { M_Name = $"Name {i}", M_GenderID = rnd.Next(1, 4), M_Mark1 = $"Mark1 {i}", M_Total = i }; } }
  }
}

Page XAML:

<Page x:Class="WpfApp40.Window40Journal"
      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:local="clr-namespace:WpfApp40"
      mc:Ignorable="d" 
      d:DesignHeight="450" d:DesignWidth="800"
      Title="Window40Journal">
  <Page.Resources>
    <CollectionViewSource x:Key="AcHeadList" Source="{Binding Tlb_Achead}"/>
  </Page.Resources>
  <DataGrid ItemsSource="{Binding Source={StaticResource AcHeadList}}"/>
</Page>

Page CodeBehind:

using System.Windows;
using System.Windows.Controls;

namespace WpfApp40
{
  public partial class Window40Journal : Page, IGridListBoxColumn
  {
    public Window40Journal()
    {
      InitializeComponent();
    }

    public object SelectedItem
    {
      get => GetValue(selecteditemProperty);
      set => SetValue(selecteditemProperty, value);
    }
    public static readonly DependencyProperty selecteditemProperty = 
      DependencyProperty.Register("SelectedItem", typeof(object), typeof(Window40Journal), 
        new PropertyMetadata(new PropertyChangedCallback(SelectedItem_Changed)));
    private static void SelectedItem_Changed(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
      IGridListBoxColumn mycontrol = sender as IGridListBoxColumn;
      mycontrol.callSelectedItem(e);
      MessageBox.Show("selected triggered");
      //not working
    }
    void IGridListBoxColumn.callSelectedItem(DependencyPropertyChangedEventArgs e)
    {
      MessageBox.Show("selected triggered");
    }
  }

  internal interface IGridListBoxColumn
  {
    void callSelectedItem(DependencyPropertyChangedEventArgs e);
  }
}