WPF Combobox event does not fire (using MVVM and Expression.Blend)-CodePudding

I am really fairly new to WPF and have just wrapped my head around MVVM / Expression.Blend.

I am trying to use the Combobox "SelectedIndexChanged" event with InvokeCommandAction, binding to a command specified in the ViewModel.

However, the code in the command is never executed (the value myvalue is never updated).

What am I doing wrong here?

XAML:

<UserControl x:Class="GDX.UI.Views.AnalyseView"
             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:i1="http://schemas.microsoft.com/xaml/behaviors" 
             xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
             xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
             xmlns:local="clr-namespace:GDX.UI.Views"
             mc:Ignorable="d" 
             Height="720" Width="1210">
    <Control.Resources>
        <ResourceDictionary Source="pack://application:,,,/GDX.UI;component/ResourceDictionary/ResourceDictionary.xaml"/>
    </Control.Resources>
<materialDesign:Card Margin="15,15,15,15" Grid.Column ="0" Grid.Row="0" Grid.RowSpan="6" Grid.ColumnSpan="2">
            <ScrollViewer Grid.Row="0" Grid.RowSpan="5" Grid.Column="0" Grid.ColumnSpan="2" VerticalScrollBarVisibility="Hidden">
                <ItemsControl ItemsSource="{Binding buildingComponents}">
                    <ItemsControl.ItemTemplate>
                        <DataTemplate>
                            <StackPanel Orientation="Vertical" Margin="10">
                                <TextBlock Margin="10" Text="{Binding Path=UIName}" FontWeight="Bold"/>
                                <ComboBox 
                                    ItemsSource="{Binding Path=ConstructionOptions}"
                                    SelectedItem="{Binding Path=Construction}"
                                    HorizontalAlignment="Center"
                                    Style="{StaticResource MaterialDesignOutlinedComboBox}"
                                    Width="256"
                                    Height="50"
                                    BorderBrush="Red"
                                    materialDesign:HintAssist.Hint="Baukonstruktion">
                                    <i:Interaction.Triggers>
                                        <i:EventTrigger EventName="SelectedIndexChanged">
                                            <i:InvokeCommandAction Command="{Binding SetBuildingComponentConstruction}"/>
                                        </i:EventTrigger>
                                    </i:Interaction.Triggers>
                                </ComboBox>
                            </StackPanel>
                        </DataTemplate>
                    </ItemsControl.ItemTemplate>
                </ItemsControl>
            </ScrollViewer>
        </materialDesign:Card>

ViewModel:

using GDX.IO.Schemas;
using GDX.IO.Statics;
using GDX.MVVM;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace GDX.ViewModel.ViewModels
{
    public class AnalyseViewModel : BaseViewModel
    {
        public ObservableCollection<BuildingComponent> buildingComponents { get; set; }
        public double myvalue { get; set; }
        public ICommand SetBuildingComponentConstruction { get; set; }

        public AnalyseViewModel()
        {
            this.buildingComponents = new ObservableCollection<BuildingComponent>();
            if (Building.BuildingComponents.Count != 0) //if contains elements
            {
                foreach (BuildingComponent bcomp in Building.BuildingComponents)
                {
                    this.buildingComponents.Add(bcomp);
                }
            }
            

            this.SetBuildingComponentConstruction = new RelayCommand(this.setBuildingComponentConstruction);
            this.myvalue = 0;
        }

        public void setBuildingComponentConstruction()
        {
         myvalue  = 1;
        }

    }
}

CodePudding user response：

Looks like the SetBuildingComponentConstruction method is defined on AnalyseViewModel, but where you are binding in the itemstemplate the datacontext would be a BuildingComponent. You may have to "walk" up to the datacontext of your UserControl.

How do I use WPF bindings with RelativeSource?

Looking at the XAML Binding Failures tab in VS while debugging may also provide you with some direction.

Try

Command="{Binding DataContext.SetBuildingComponentConstruction,
          RelativeSource={RelativeSource AncestorType=ComboBox}}"