Datagrid binding MVVM

Question

I'm very new to MVVM and I am just trying to get my feet wet with a small testing wpf application. I have a Model call ToDoItemModel defined as below: (basically I have a class called ToDoItemModel and ToDoItemListModel which implements IList

public class ToDoItemModel
{
    private DateTime    _TodoDate;
    private string      _TodoDescription;
    private TimeSpan    _TodoTimeSpan;
    private string      _StartTime;

    public ToDoItemModel(DateTime d, string s)
    {
        _TodoDate=d;
        _TodoDescription=s;
    }

    public string StartTime
    {
        get { return      _StartTime; }
        set {      _StartTime = value; }
    }


    public TimeSpan ToDoTimeSpan
    {
        get { return _TodoTimeSpan; }
        set { _TodoTimeSpan = value; }
    }

    public string ToDoDescription
    {
        get { return _TodoDescription; }
        set { _TodoDescription = value; }
    }

    public DateTime ToDoDate
    {
        get { return _TodoDate; }
        set { _TodoDate = value; }
    }

    public override string ToString()
    {
        return string.Format("Date: {0}- Time: {1}- Duration: {2}- Description: {3}",_TodoDate.ToString("d"),_StartTime,_TodoTimeSpan,_TodoDescription);
    }       
}

public class ToDoListModel: IList<ToDoItemModel>
{
    private readonly IList<ToDoItemModel> _todoList = new List<ToDoItemModel>();

    public ToDoListModel()
    {
         //Hard code this one for testing purpose
        _todoList.Add(new ToDoItemModel(DateTime.Now,"Testing"));
    }

    public int IndexOf(ToDoItemModel item)
    {
        return _todoList.IndexOf(item);
    }

    public void Insert(int index, ToDoItemModel item)
    {
        _todoList.Insert(index,item);
    }

    public void RemoveAt(int index)
    {
        _todoList.RemoveAt(index);
    }

    public ToDoItemModel this[int index]
    {
        get
        {
            return _todoList[index];
        }
        set
        {
            _todoList[index]=value;
        }
    }

    public void Add(ToDoItemModel item)
    {
        _todoList.Add(item);
    }

    public void Clear()
    {
        _todoList.Clear();
    }

    public bool Contains(ToDoItemModel item)
    {
        return _todoList.Contains(item);
    }

    public void CopyTo(ToDoItemModel[] array, int arrayIndex)
    {
        _todoList.CopyTo(array,arrayIndex);
    }

    public int Count
    {
        get { return _todoList.Count; }
    }

    public bool IsReadOnly
    {
        get { return _todoList.IsReadOnly; }
    }

    public bool Remove(ToDoItemModel item)
    {
        return _todoList.Remove(item);
    }

    public IEnumerator<ToDoItemModel> GetEnumerator()
    {
        return _todoList.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

I would like to display on my view a datagrid that is going to bind to ToDoListModel through ToDoListModelView which inherits from ObservableObject. ObservableObject implements INotifyPropertyChanged

public class ToDoListModelView:ObservableObject
{
    ToDoListModel _myModel = new ToDoListModel();
    ...
}

My view is defined by xaml code below: Basically, I would like to bind that datagrid to my ToDoListModel.

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:TestWPF" x:Class="TestWPF.MainWindow"
        Title="MainWindow" Height="350" Width="525">
    <Grid Margin="1,0,-1,0">
        <DataGrid x:Name="ExistingToDoList" 
          HorizontalAlignment="Left" 
          Margin="33,201,0,0" 
          VerticalAlignment="Top" 
          Height="94" Width="464" 
          Background="#FFF1E6E6" 
          GridLinesVisibility="Horizontal" 
          ItemsSource="{Binding ToDoListModelView}" 
          Style="{DynamicResource ToDoEntry}">
            <DataGrid.DataContext>
                <local:ToDoListModel/>
            </DataGrid.DataContext>
        </DataGrid>
    </Grid>
</Window>

However, after hitting F5, the program ran but I do not see content bound to the data although I do have at least 1 item in the list. What have I done incorrectly? I know it is far from being complete but at the very least, I should see the ToDoItem in the list from the datagrid? What have I missed? Please help. Thanks!

---- My Update ----------------------------------------------

ToDoListModel inherits from List with property ToDoList that return the underlying data

public class ToDoListModel: List<ToDoItemModel>
{
    private  List<ToDoItemModel> _todoList = new List<ToDoItemModel>();
    public List<ToDoItemModel> TodoList
    {
        get { return _todoList; }
    }

    public ToDoListModel()
    {
        _todoList.Add(new ToDoItemModel(DateTime.Now,"Testing"));
    }

I have also corrected the datagrid to bind to ToDoList and set autoGeneratecolumn to true for simplicity and illustration sake.

<Grid Margin="1,0,-1,0" d:DataContext="{d:DesignData /SampleData/ToDoListModelSampleData.xaml}">
    <DataGrid x:Name="ExistingToDoList" 
        HorizontalAlignment="Left" 
        Margin="33,201,0,0" 
        VerticalAlignment="Top" 
        Height="94" Width="464" 
        Background="#FFF1E6E6" 
        GridLinesVisibility="Horizontal" 
        ItemsSource="{Binding TodoList}" 
        Style="{DynamicResource ToDoEntry}" 
        AutoGenerateColumns="True"
        DataContext="{Binding Mode=OneWay}">
        <DataGrid.ItemBindingGroup>
            <BindingGroup/>
        </DataGrid.ItemBindingGroup>
    </DataGrid>

Answer 1

You set your DataContext property to the "Model" class (something you should never do, always set to a ViewModel class) which does not have a property called "ToDoListModelView", so the binding is failing (you should see this as a System.Data exception in the output window).

Writing ItemsSource="{Binding ToDoListModelView}" says "Look for a property called 'ToDoListModelView' on my DataContext and use it as my ItemsSource". What you probably intended to do was:

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:TestWPF" x:Class="TestWPF.MainWindow"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
       <local:ToDoListModelView/>
    </Window.DataContext>
    <Grid Margin="1,0,-1,0">
        <DataGrid x:Name="ExistingToDoList" 
          ItemsSource="{Binding MyModelProperty}" 
        </DataGrid>
    </Grid>
</Window>

Note that I set the DataContext to a ViewModel object (not a Model) and I set it for the window. This is purely stylistic, but you normally don't set specific control's DataContext property (though there are times when it is necessary). I then bind to a (imaginary) property that would probably be an instance of ToDoListModel.

A few other asides:

1. If you are inheriting IList you are probably doing it wrong! What's wrong with ObservableCollection or one of the other existing implemenations?
2. Its "ViewModel" not "ModelView", just as a naming convention

Similar, but not a duplicate (the answer could help you: Setting DataContext in XAML in WPF)