MVVM binding error?

0
votes

In the first block below I intentionally miss named one of my binding statements so I could compare to my second block. The difference is in the property not found on 'ag2.item...' line.
item is my model.

In block 2 you can see that it is pointing to my view model (ag2.viewModel.itemViewModel).

What do I need to do in my XAML or my codebehind to get it to point to my class rather than the viewmodel?

Block 1:

BindingExpression path error: 'itemModel1' property not found on 'ag2.item, ag2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. BindingExpression: Path='itemModel1' DataItem='ag2.item, ag2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; target element is 'Windows.UI.Xaml.Controls.TextBlock' (Name='null'); target property is 'Text' (type 'String')

Block 2:

BindingExpression path error:'itemModel' property not found on 'ag2.viewModel.itemViewModel, ag2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. BindingExpression: Path='itemModel' DataItem='ag2.viewModel.itemViewModel, ag2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; target element is 'Windows.UI.Xaml.Controls.TextBlock' (Name='null'); target property is 'Source' (type 'String')

Code behind to Block 2:

    itemViewModel VM = new itemViewModel((Int32)navigationParameter);
    DataContext = VM;

I should also note that in block 1 I am doing my binding to a GridView where the ItemSource="{Binding item}" is set.

In block 2 I built my UI using grids and textblocks using this: Text="{Binding Path=itemModel}"

Update: In an effort to try to gain better understanding. I'm putting my code out there: Here is the XAML, below that will be the ViewModel and below that is my Model... I'm new at MVVM so I really don't know what I'm doing incorrectly. Any help is greatly appreciated.

XAML:

<common:LayoutAwarePage
    x:Name="pageRoot"
    x:Class="autoGarage2.VehicleItemDetailPage"
    IsTabStop="false"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:common="using:autoGarage2.Common"
    xmlns:local="using:autoGarage2"
    xmlns:data="using:autoGarage2"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006">


    <!--
        This grid acts as a root panel for the page that defines two rows:
        * Row 0 contains the back button and page title
        * Row 1 contains the rest of the page layout
    -->
    <Grid Style="{StaticResource LayoutRootStyle}">

        <Grid.RowDefinitions>
            <RowDefinition Height="140"/>
            <RowDefinition Height="2*"/>
        </Grid.RowDefinitions>

        <!-- Back button and page title -->
        <Grid
         Style="{StaticResource LayoutRootStyle}" Grid.Row="0">

            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Button x:Name="backButton" Click="GoBack" IsEnabled="{Binding Frame.CanGoBack, ElementName=pageRoot}" Style="{StaticResource BackButtonStyle}"/>
            <TextBlock x:Name="pageTitle" Text="{StaticResource AppName}" Style="{StaticResource PageHeaderTextStyle}" Grid.Column="1"/>
        </Grid>



        <Grid Grid.Row="1">


            <Grid.ColumnDefinitions>
               <ColumnDefinition Width="Auto"/> 
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="3*"/>
                <RowDefinition Height="1*"/>
            </Grid.RowDefinitions>


                <StackPanel Grid.Row="0" Orientation="Horizontal" Width="auto" Margin="50,0,0,0" VerticalAlignment="Top"  >
                    <Grid HorizontalAlignment="Left" Width="250" Height="250">
                        <Border Background="White" BorderBrush="CornflowerBlue" BorderThickness="1">
                                <Image Source="{Binding Image}" Margin="50"/>
                            </Border>
                            <StackPanel VerticalAlignment="Bottom" Background="CornflowerBlue">
                                <StackPanel Orientation="Horizontal" DataContext="{Binding vehicles}">
                                <TextBlock Text="{Binding VehicleMake}" Foreground="{StaticResource ListViewItemOverlayForegroundThemeBrush}" Style="{StaticResource PageSubheaderTextStyle}" Margin="5"/>
                                <TextBlock Text="{Binding VehicleModel}" Foreground="{StaticResource ListViewItemOverlaySecondaryForegroundThemeBrush}" Style="{StaticResource PageSubheaderTextStyle}" Margin="5"/>
                                </StackPanel>
                            </StackPanel>
                        </Grid>
                </StackPanel>
                    <StackPanel Grid.Row="0" Grid.Column="1">
                        <Grid Margin="20,0,0,20">
                            <Grid.RowDefinitions>
                                <RowDefinition Height="1*"/>
                                <RowDefinition Height="1*"/>
                                <RowDefinition Height="1*"/>
                                <RowDefinition Height="1*"/>                                
                                <RowDefinition Height="1*"/>                                
                                <RowDefinition Height="1*"/>
                                <RowDefinition Height="1*"/>
                                <RowDefinition Height="1*"/>
                                <RowDefinition Height="1*"/>                                
                                <RowDefinition Height="1*"/>    
                                <RowDefinition Height="1*"/> 
                                <RowDefinition Height="1*"/> 
                                <RowDefinition/>                                
                            </Grid.RowDefinitions>

                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="1*"/>
                                <ColumnDefinition Width="1*"/>
                                <ColumnDefinition Width="2*"/>
                            </Grid.ColumnDefinitions>






                            <TextBlock Text="Vehicle Make:" Grid.Row="0" Grid.Column="0" FontSize="25" Foreground="Black" />
                            <TextBox Text="{Binding Path=VehicleMake}"  Grid.Row="0" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>

                            <TextBlock Text="Vehicle Model:" FontSize="25" Foreground="Black" Grid.Row="1" Grid.Column="0"/>
                            <TextBox Text="{Binding VehicleModel}"  Grid.Row="1" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>                            

                            <TextBlock Text="Vehicle Year:" FontSize="25" Foreground="Black" Grid.Row="2" Grid.Column="0"/>
                            <TextBox Text="{Binding VehicleYear}"  Grid.Row="2" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>

                            <TextBlock Text="License Plate:" FontSize="25" Foreground="Black" Grid.Row="3" Grid.Column="0"/>
                            <TextBox Text=""  Grid.Row="3" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/> 

                            <TextBlock Text="VIN #" FontSize="25" Foreground="Black" Grid.Row="4" Grid.Column="0"/>
                            <TextBox Text=""  Grid.Row="4" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1" />    

                            <TextBlock Text=" Current Mi/Km" FontSize="25" Foreground="Black" Grid.Row="5" Grid.Column="0"/>
                            <TextBox Text=""  Grid.Row="5" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>              

                            <TextBlock Text="" FontSize="25" Foreground="Black" Grid.Row="6" Grid.ColumnSpan="2"/>

                            <TextBlock Text="Last Oil Change" FontSize="25" Foreground="Black" Grid.Row="7" Grid.Column="0"/>
                            <TextBox Text=""  Grid.Row="7" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>              

                            <TextBlock Text="Last Oil Change Mi/Km" FontSize="25" Foreground="Black" Grid.Row="8" Grid.Column="0"/>
                            <TextBox Text=""  Grid.Row="8" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>

                            <TextBlock Text="" FontSize="25" Foreground="Black" Grid.Row="9" Grid.ColumnSpan="2"/>

                            <TextBlock Text="Reminder Mi/Km" FontSize="25" Foreground="Black" Grid.Row="10" Grid.Column="0"/>
                            <TextBox Text=""  Grid.Row="10" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>     

                            <TextBlock Text="Reminder Month(s)" FontSize="25" Foreground="Black" Grid.Row="11" Grid.Column="0"/>
                            <TextBox Text=""  Grid.Row="11" Grid.Column="1" FontSize="25" BorderBrush="CornflowerBlue" BorderThickness="1"/>                          

                        </Grid>                     
                </StackPanel>

            </Grid>

    </Grid>
</common:LayoutAwarePage>

View Model:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.ObjectModel;
using Windows.Foundation.Collections;
using System.IO;


namespace autoGarage2.viewModel
{
    class vehicleViewModel
    {
        private IList<vehicle> m_vehicles;
        private IList<vehicle> m_vehicleItem;

        public IList<vehicle> vehicles
        {
            get { return m_vehicles; }
            set { m_vehicles = value; }
        }

        public IList<vehicle> vehicleItem
        {
            get { return m_vehicleItem; }
            set { m_vehicleItem = value; }
        }

        private IList<vehicle> getVehicleDetail(Int32 vId)
        {
            var vehicleItem =
                from v in vehicles
                where v.VehicleId == vId
                select v;
            if (vId > 0)
            {
                //vehicles.Clear();
                m_vehicles = new List<vehicle>();
                foreach (var item in vehicleItem)
                {
                    m_vehicles = new List<vehicle>
                    {
                        new vehicle(item.VehicleId, item.VehicleMake.ToString(), item.VehicleModel.ToString(), item.VehicleYear, item.Image.ToString())
                    };
                    //vehicle myVehicle = new vehicle(item.VehicleId, item.VehicleMake.ToString(), item.VehicleModel.ToString(), item.VehicleYear, item.Image.ToString());
                    //m_vehicles.Add(myVehicle);
                }

            }

            return m_vehicles;
        }

        public vehicleViewModel(Int32 vId)
        {
                m_vehicles = new List<vehicle>
                {        
                new vehicle(1, "Mazda", "3", 2011, "Assets/car2.png"),
                new vehicle(2, "Chevy", "Tahoe", 2004, "Assets/jeep1.png"),
                new vehicle(3, "Honda", "Goldwing", 2007 ,"Assets/moto1.png")
                };

                if (vId > 0)
                {
                    //m_vehicles = new List<vehicle>();
                    //m_vehicles = 
                    //getVehicleDetail(vId);
                    m_vehicles = new List<vehicle>
                    {        
                    new vehicle(2, "Chevy", "Tahoe", 2004, "Assets/jeep1.png"),
                    };

                }
        }



        #region dbCode

        //string dbName = "vehicle.db";


        //var dbPath = Path.Combine(Windows.Storage.ApplicationData.Current.LocalFolder.Path, dbName);    
        //using (var db = new SQLite.SQLiteConnection(dbPath))    
        //    {
        //        var list = db.Table<vehicle>().ToList();
        //        m_vehicles = new List<vehicle>();
        //        for (Int32 i = 0; i < list.Count; i++)
        //        {
        //            //m_vehicles.Add(db.Table<vehicle>().ToList());
        //        }
        //    }




        //foreach (vehicle item in m_vehicles)
        //{
        //    AllItems.Add(item);
        //}      
        #endregion

    }
}

Model:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
//using SQLite;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Media.Imaging;

namespace autoGarage2
{
    class vehicle : autoGarage2.Common.BindableBase
    {
        public vehicle()
        { 
        }

        public vehicle(string imagePath)
        {
            this._imagePath = imagePath;
        }
        public vehicle(Int32 vId, string vMake, string vModel, Int16 vYear, string imagePath)
        {
            this.m_vehicleID = vId;
            this.m_vehicleMake = vMake;
            this.m_vehicleModel = vModel;
            this.m_vehicleYear = vYear;
            this.m_vehicleName = vMake + " " + vModel;
            this._imagePath = imagePath;
        }


        private Int32 m_vehicleID;

        private String m_vehicleMake;
        private String m_vehicleModel;
        private Int16 m_vehicleYear;
        private string m_vehicleName;


        private ImageSource _image = null;
        private String _imagePath = null;
        private static Uri _baseUri = new Uri("ms-appx:///");

        //[AutoIncrement, PrimaryKey]
        public Int32 VehicleId
        {
            get
            {
                return m_vehicleID;
            }
            set
            {
                m_vehicleID = value;
                OnPropertyChanged("VehicleId");
            }
        }

        public String VehicleMake
        {
            get
            {
                return m_vehicleMake;
            }
            set
            {
                m_vehicleMake = value;
                OnPropertyChanged("VehicleMake");
            }
        }

        public String VehicleModel
        {
            get
            {
                return m_vehicleModel;
            }
            set
            {
                m_vehicleModel = value;
                OnPropertyChanged("VehicleModel");
            }
        }
    public Int16 VehicleYear
    {
        get
        {
            return m_vehicleYear;
        }
        set
        {
            m_vehicleYear = value;
            OnPropertyChanged("VehicleYear");
        }
    }

    public string VehicleName
    {
        get
        {
            return m_vehicleName;
        }
        set
        {
            m_vehicleName = value;
            OnPropertyChanged("VehicleName");
        }
    }

    public ImageSource Image
    {
        get
        {
            if (this._image == null && this._imagePath != null)
            {
                this._image = new BitmapImage(new Uri(vehicle._baseUri, this._imagePath));
            }
            return this._image;
        }

        set
        {
            this._imagePath = null;
            this.SetProperty(ref this._image, value);
        }
    }

    public void SetImage(String path)
    {
        this._image = null;
        this._imagePath = path;
        this.OnPropertyChanged("Image");
    }
}

}

3
xamlwindows-runtimewinrt-xaml
It's a bit unclear what you are doing and what you want to achieve. What is the structure of your view model? What is the structure of your XAML? Are you trying to bind to itemModel? Where is itemModel defined? – Filip Skakun
please see updated question. I added everything. If you can help it would be GREATLY appreciated – webdad3
Please also clarify the problem you're having. The issue above seems to reference a binding error with ItemModel, however there are no bindings to ItemModel in your XAML. Which TextBox is causing the error, and what would you like it to bind to? Where is your DataContext set for the view? – Brian S

3 Answers

1
votes

It sounds like you are trying to databind your TextBlock to a different object, not to the ViewModel (which is the DataContext of your window/control). If that is correct, you'll need to set the DataContext of the TextBlock or the parent Grid to the object you want to DataBind to.

The DataContext is used in determining the path to DataBind to for a control, and it inherits down the visual tree. So if your DataContext is set to MyViewModel, and you use Text="{Binding Path=itemModel}", your binding path will be MyViewModel.itemModel.

If you don't want to include MyViewModel in the binding path, you'll need to change the DataContext of the control in question, or of a containing control. For MVVM, this is often done by having the other object exposed as a property of the ViewModel. So if your MyViewModel had a property ItemModel:

public class ItemModel
{
    public string Property1 { get; }
    public string Property2 { get; }
}

public class MyViewModel
{
    public ItemModel ItemModel { get; private set; }
}

Then your XAML could look like this (assuming MyViewModel is the DataContext of the parent window/control).

<Grid Grid.Row="1" DataContext="{Binding ItemModel}">
    <Grid.RowDefinitions>
        <RowDefinition/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <TextBlock Text="{Binding property1}"/>
    <TextBlock Text="{Binding Property2}" Grid.Row="1"/>
</Grid>

And the two textboxes would be bound to Property1 and Property2 of the ItemModel object.

1
votes

You seem to be trying to bind to a list but you are not using any ItemsControl in your XAML. You should probably use something like a ListView, bind its ItemsSource to your vehicles or vehicleItem lists, use an ItemTemplate/DataTemplate to define the look of each item in the collection, use ObservableCollection if your collection changes or raise INotifyPropertyChanged.PropertyChanged notifications if you swap out your collection, etc. Otherwise I would suggest reading something about binding ItemsControls or a general book about XAML, like Adam Nathan's WPF Unleashed. It seems like you are setting your m_vehicles only to replace it with a new one in the next statement. Also - you are setting the DataContext of the StackPanel to your list, which is allowed, but it does not work, since the DataContext of the elements of your StackPanel will still be the entire list and not its items, which is what you get by using an ItemsControl.

0
votes

I was able to get my data to show up after a weekend of not looking at it. Basically I noticed that I was getting a binding error that stated that it couldn't find the property in my autoGarage2.vehicles list. So for grins I prefaced the binding like this:

{Binding vehicles[0].vehicleModel}

Next time I ran it, the data was there. After thinking about it some more, I decided to create a single object of vehicle and instead of populating the list object I'm populating just the single vehicle property. Now I'm doing something like this:

{Binding vehicleSingle.vehicleModel}

Thanks for every ones help. I guess this is just a nuance of how MVVM works in XAML...