Set Property in Viewmodel from Code Behind

Question

I think I am overthinking this at this point, but I have a unique situation.

Using a treeviewI am displaying a table and the fields in that table:

XAML:

        <TreeView x:Name="myTreeView" PreviewMouseDoubleClick="myTreeView_MouseLeftButtonDown" SelectedValuePath="Name" ItemsSource="{Binding Fields}" ItemContainerStyle="{StaticResource TreeViewItemExpandedStyle}">
            <TreeView.ItemTemplate>
                <HierarchicalDataTemplate ItemsSource="{Binding Fields}">
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Foreground="Black" Text="{Binding Table}" />                               
                    </StackPanel>
                    <HierarchicalDataTemplate.ItemTemplate>
                        <DataTemplate>
                            <StackPanel Orientation="Horizontal">
                                <Button BorderBrush="Transparent"
                                        Background="White" 
                                        Command="">
                                    <StackPanel>
                                        <Path Margin="5" 
                                      Data="M0,5 H10 M5,5 V10Z" 
                                      Stroke="#2283B4" 
                                      StrokeThickness="1" 
                                      Height="10" 
                                      Width="10" />
                                    </StackPanel>
                                </Button>
                                <StackPanel Orientation="Horizontal">
                                    <TextBlock Text="{Binding Name}" />
                                    <TextBlock Height="0" Width="0" Visibility="Collapsed" Text="{Binding Table}"/>
                                </StackPanel>
                            </StackPanel>
                        </DataTemplate>
                    </HierarchicalDataTemplate.ItemTemplate>
                    <!--<HierarchicalDataTemplate.Triggers>
                        <DataTrigger Binding="{Binding IsExpanded}" Value="True">
                            <Setter TargetName="treeIcon"
                                    Property="Data"
                                    Value="M0,5 H10"/>
                        </DataTrigger>
                    </HierarchicalDataTemplate.Triggers>-->
                </HierarchicalDataTemplate>
            </TreeView.ItemTemplate>

        </TreeView>

Example:

These treeviews are also their own user controls. The issue I am having is I need to be able to use the selected treeview item in another viewmodel. I also have found no other way to grab the selected treeview item and parent except through the code behind. Below is my entire code behind section for this control.

SourceRowUserControl.xaml.cs:

using Alliance.FromAnywhereControl.Models;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
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.Navigation;
using System.Windows.Shapes;
using Alliance.FromAnywhereControl.ViewModels;
using System.Reflection;

namespace Alliance.FromAnywhereControl
{
    /// <summary>
    /// Interaction logic for SourceRowUserControl.xaml
    /// </summary>
    public partial class SourceRowUserControl : UserControl
    {
        public SourceRowUserControl()
        {
            InitializeComponent();
        }

        private ObservableCollection<ConversionRowUserControl> ConversionTypes = new ObservableCollection<ConversionRowUserControl>();

        public ObservableCollection<TableInformation> Fields
        {
            get { return (ObservableCollection<TableInformation>)GetValue(FieldsProperty); }
            set { SetValue(FieldsProperty, value); }
        }

        // Using a DependencyProperty as the backing store for Fields.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty FieldsProperty =
            DependencyProperty.Register("Fields", typeof(ObservableCollection<TableInformation>), typeof(SourceRowUserControl), new PropertyMetadata(TableInformation.GetAll(null, null, null, null)));


        public String FileTypeImage
        {
            get { return (String)GetValue(FileTypeImageProperty); }
            set { SetValue(FileTypeImageProperty, value); }
        }

        // Using a DependencyProperty as the backing store for FieldTypeImage.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty FileTypeImageProperty =
            DependencyProperty.Register("FileTypeImage", typeof(String), typeof(SourceRowUserControl), new PropertyMetadata("File Type Image"));

        public SolidColorBrush SpacerColor
        {
            get { return (SolidColorBrush)GetValue(SpacerColorProperty); }
            set { SetValue(SpacerColorProperty, value); }
        }

        // Using a DependencyProperty as the backing store for SpacerColor.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SpacerColorProperty =
            DependencyProperty.Register("SpacerColor", typeof(SolidColorBrush), typeof(SourceRowUserControl), new PropertyMetadata(new SolidColorBrush(Colors.Red)));


        public String MiddleLabel
        {
            get { return (String)GetValue(MiddleLabelProperty); }
            set { SetValue(MiddleLabelProperty, value); }
        }

        // Using a DependencyProperty as the backing store for MiddleLabel.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty MiddleLabelProperty =
            DependencyProperty.Register("MiddleLabel", typeof(String), typeof(SourceRowUserControl), new PropertyMetadata("Middle Label"));

        private void myTreeView_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            try
            {

                Field selectedField = new Field();

                selectedField = (Field)myTreeView.SelectedItem;

                ConversionViewModel cvm = new ConversionViewModel();

                cvm.AddConversionType(selectedField.Table, selectedField.Name);         
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

    }
}

The myTreeViewLeftButtonDown event is where is I am grabbing the selected field and table. As you see, I am then calling a method in another viewmodel, but this will not work how I want it to since it creates a new instance. I just put that there to basically show what I was wanting to do. Overview, I need to be able to use a field in my code behind in a viewmodel that is not connected to the view.

Please let me know if you need anymore information or would like to see more code. Thanks in advance!

Answer 1

Looking at your code, instead of defining new ConversionViewModel(), grab the instance of the ConversionViewModel and then set property on it.

public class ConversionViewModel()
{
    private static ConversionViewModel _this;
    public ConversionViewModel()
        {
            InitializeComponent();
            _this = this;
        }

        public static ConversionViewModel GetInstance()
        {
            return _this;
        }

      //Other prop and methods
}

private void myTreeView_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            try
            {

                Field selectedField = new Field();

                selectedField = (Field)myTreeView.SelectedItem;

               ConversionViewModel.GetInstance().AddConversionType(selectedField.Table, selectedField.Name);                       
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

Answer 2

You can give your ItemTemplate an InputBinding to the Left Button Click action.

<DataTemplate>
    <StackPanel Orientation="Horizontal">
        <StackPanel.InputBindings>
            <MouseBinding MouseAction="LeftClick"
                          Command="{Binding DataContext.SomeViewModelCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=TreeView}}"
                          CommandParameter="{Binding}"/>
        </StackPanel.InputBindings>
        ...
    </StackPanel>
</DataTemplate>

To help explain this, the MouseBinding specifies what command to execute when the LeftClick occurs on the StackPanel .

The Command is bound to the DataContext.SomeViewModelCommand from your TreeView .

The CommandParameter is the Field bound to the DataTemplate .

Now, all you need to do is declare a Command in your View Model ( SomeViewModelCommand ) where the Command Parameter will be your Field .