Binding WPF DataGrid to List<Interface>

Question

Hello I have a DataGrid and I have different reports that I want to show. I'm going to change the classes so they are shorter in here but Idea is the same.

Lets say that I Have an Interface called IReports

public interface IReports
{
}

and three classes called Students, Classes, Cars

public class Students:IReports
{
    public string Name { get; set; }
}  

public class Classes : IReports
{
    public string ClassName { get; set; }
    public string StudentName { get; set; }

}   
public class Cars : IReports
{
    public int Mileage { get; set; }
    public string CarType { get; set; }
    public string StudentName { get; set; }
}

The List

private List<IReports> _reportsTable;    

public List<IReports> ReportsTable
    {
        get { return _reportsTable; }
        set { SetProperty(ref (_reportsTable), value); }
    }

the DataGrid

<DataGrid ItemsSource="{Binding ReportsList}"
          Grid.Column="1"
          Grid.Row="0"
          AutoGenerateColumns="True"
          Grid.RowSpan="6"/>

Okay, so what is important here is they all have different property names and some have more some have less. How can I bind the DataGrid to look at the different properties? This is MVVM if that makes any difference.

Update: What this will always only use one of the classes at a time.but when someone changes a combobox it will fire an event that will fill the IList<IReports>.

Answer 1

What this will always only use one of the classes at a time. but when someone changes a combobox it will fire an event that will fill the IList<IReports>.

The way I understand the above is that you never mix different elements inside the list (i.e. it contains only Classes, Students or Cars). All the other answers are assuming the list contains mixed content, but if that's the true, then DataGrid is simply not the right presenter for such content.

If the above assumption is correct, then the only problem is how to represent different lists with a single bindable property. As can be seen in Data Binding Overview, when dealing with collection, data binding does not really care if they are generic or not. The recognizable source types are the non generic IEnumerable, IList and IBindingList. However, the collection view implementation is using some rules to determine the element type of the collection, by seeking for generic type argument of implemented IEnumerable<T> interfaces by the actual data source class, by checking the first available item, or taking the information from ITypedList implementation etc. All the rules and their precedence can be seen in the Reference Source.

With all that in mind, one possible solution could be to change the ReportsTable property type to allow assigning List<Classes> or List<Students or List<Cars>. Any common class/interface will work (remember, data binding will check the actual type returned by GetType()) like object, IEnumerable, IList, IEnumerable<IReports> etc., so I'll choose the closest covariant type to List<IReports which is IReadOnlyList<IReports>:

private IReadOnlyList<IReports> _reportsTable;

public IReadOnlyList<IReports> ReportsTable
{
    get { return _reportsTable; }
    set { SetProperty(ref (_reportsTable), value); }
}

Now when you do this

viewModel.ReportsTable = new List<Students>
{
    new Students { Name = "A" },
    new Students { Name = "B" },
    new Students { Name = "C" },
    new Students { Name = "D" },
};

you get

while with this

viewModel.ReportsTable = new List<Classes>
{
    new Classes { ClassName = "A", StudentName = "A" },
    new Classes { ClassName = "A", StudentName ="B" },
    new Classes { ClassName = "B", StudentName = "C" },
    new Classes { ClassName = "B", StudentName = "D" },
};

it shows

and finally this

viewModel.ReportsTable = new List<Cars>
{
    new Cars { Mileage = 100, CarType = "BMW", StudentName = "A" },
    new Cars { Mileage = 200, CarType = "BMW", StudentName = "B" },
    new Cars { Mileage = 300, CarType = "BMW", StudentName = "C" },
    new Cars { Mileage = 400, CarType = "BMW", StudentName = "D" },
};

results in

UPDATE: The above requires modifying the model to return concrete List<T> instances. If you want to keep the model as it is (i.e. returning List<IReports>), then you'll need a different solution, this time utilizing the ITypedList. In order to do that, we'll create a simple list wrapper using the System.Collections.ObjectModel.Collection<T> base class:

public class ReportsList : Collection<IReports>, ITypedList
{
    public ReportsList(IList<IReports> source) : base(source) { }
    public PropertyDescriptorCollection GetItemProperties(PropertyDescriptor[] listAccessors)
    {
        return TypeDescriptor.GetProperties(Count > 0 ? this[0].GetType() : typeof(IReports));
    }
    public string GetListName(PropertyDescriptor[] listAccessors) { return null; }
}

then change the bindable property to

private IList<IReports> _reportsTable;
public IList<IReports> ReportsTable
{
    get { return _reportsTable; }
    set { SetProperty(ref _reportsTable, value as ReportsList ?? new ReportsList(value)); }
}

and you are done.

Answer 2

Instead of a converter option to display a given string value, why not add a getter to the base interface. Then, each class just returns its own, almost like every object can override its "ToString()" method Since you would create a list such as for display, or picking, the value would be read-only anyhow, Make it just a getter...

public interface IReports
{
    string ShowValue {get;}
}

public class Students:IReports
{
    public string Name { get; set; }
    public string ShowValue { get { return Name; } }
}  

public class Classes : IReports
{
    public string ClassName { get; set; }
    public string StudentName { get; set; }
    public string ShowValue { get { return ClassName + " - " + StudentName ; } }
}   
public class Cars : IReports
{
    public int Mileage { get; set; }
    public string CarType { get; set; }
    public string StudentName { get; set; }
    public string ShowValue { get { return CarType + "(" + Mileage + ") - " + StudentName; } }
}

Then in your view model manager...

public class YourMVVMClass
{
        public YourMVVMClass()
        {
           SelectedRptRow = null;
           ReportsTable = new List<IReports>() 
           {
               new Students() { Name = "Student 1" },
               new Students() { Name = "Student 2" },
               new Classes() { ClassName="CS 101", StudentName = "Student 3" },
               new Cars() { CarType = "Truck", Mileage=12345, StudentName = "Student 4" }
           };
        }


        // This get/set for binding your data grid to
        public List<IReports> ReportsTable { get; set; }
        // This for the Selected Row the data grid binds to
        public IReports SelectedRptRow { get; set; }

        // This for a user double-clicking to select an entry from
        private void Control_OnMouseDoubleClick(object sender, MouseButtonEventArgs e)
        {
            // Now, you can look directly at the SelectedRptRow
            // as in the data-grid binding declaration.
            if (SelectedRptRow is Classes)
                MessageBox.Show("User selected a class item");
            else if( SelectedRptRow is Cars)
                MessageBox.Show("User selected a car item");
            else if( SelectedRptRow is Students)
                MessageBox.Show("User selected a student item");
            else
                MessageBox.Show("No entry selected");
        }
}

Finally in your form/view

    <DataGrid Grid.Row="0" Grid.Column="0"
        ItemsSource="{Binding ReportsTable}"
        SelectedItem="{Binding SelectedRptRow}" 
        MouseDoubleClick="Control_OnMouseDoubleClick"
        AutoGenerateColumns="False" 
        Width="200" Height ="140" 
        HorizontalAlignment="Left"
        VerticalAlignment="Top">

        <DataGrid.Columns>
            <DataGridTextColumn 
                Header="Report Item" 
                Width="180"
                IsReadOnly="True"
                CanUserSort="False"
                Binding="{Binding Path=ShowValue}" />
        </DataGrid.Columns>
    </DataGrid>

The other answers using the converters are just another path, but this avenue to me is easier as you can change each individual class and expand / adjust as needed. The exposed "ShowValue" getter is common to all instances of the "IReports", so the binding is direct without going through the converter. If you remove a class, or extend in the future, your underlying is all self-contained.

Now don't get me wrong, I do use converters and typically do with Boolean type fields to respectively show, hide, collapse controls as needed. This is nice as I have different boolean converters such as

BoolToVisibleHidden = if True, make visible vs Hidden
BoolToHiddenVisible = if True, make Hidden vs Visible
BoolToVisibleCollapse = if True, make visible vs Collapsed
BoolToCollapseVisible = if True, make Collapsed vs visible.

So, with one boolean property on my MVVM, I can both show AND hide different controls... maybe such as an admin vs standard user option.

I've also used converters dealing with dates for alternate formatting purposes.

Answer 3

As I understand it, you want a datagrid to show the various columns of various classes that implement an interface. If you hook the DataGrid's LoadingRow event, you can see what types of objects you are dealing with at runtime. You can use reflection to get the properties off the row's datacontext and then check the datagrid to see if there is a column for that property. If not, add it.

An issue will be if there are different types in the list and a type doesn't have a property that is in another type (like Cars doesn't have a Name property and both Students and Cars are in the list). If you edit a column for a property that doesn't exist on the object, you'll throw an exception. To get around this, you'll need a converter and style that applies it to the datagridcells. For fun, I also added a datatrigger that changes the background of the cell to Silver if it is disabled. One issue will be if you need to change the cell's style then you have to do it in the code (or change the style in the code to be based on your style).

XAML:

<DataGrid ItemsSource="{Binding ReportsTable}" AutoGenerateColumns="True" LoadingRow="DataGrid_LoadingRow" />

CS

private void DataGrid_LoadingRow(object sender, DataGridRowEventArgs e)
{
    var dg = sender as DataGrid;
    var pis = e.Row.DataContext.GetType().GetProperties();
    foreach (var pi in pis)
    {
        // Check if this property already has a column in the datagrid
        string name = pi.Name;
        var q = dg.Columns.Where(_ => _.SortMemberPath == name);
        if (!q.Any())
        {
            // No column matches, so add one
            DataGridTextColumn c = new DataGridTextColumn();
            c.Header = name;
            c.SortMemberPath = name;
            System.Windows.Data.Binding b = new Binding(name);
            c.Binding = b;

            // All columns don't apply to all items in the list
            // So, we need to disable the cells that aren't applicable
            // We'll use a converter on the IsEnabled property of the cell
            b = new Binding();
            b.Converter = new ReadOnlyConverter();
            b.ConverterParameter = name;

            // Can't apply it directly, so we have to make a style that applies it
            Style s = new Style(typeof(DataGridCell));
            s.Setters.Add(new Setter(DataGridCell.IsEnabledProperty, b));
            // Add a trigger to the style to color the background when disabled
            var dt = new DataTrigger() { Binding = b, Value = false };
            dt.Setters.Add(new Setter(DataGridCell.BackgroundProperty, Brushes.Silver));
            s.Triggers.Add(dt);
            c.CellStyle = s;

            // Add the column to the datagrid
            dg.Columns.Add(c);
        }
    }
}

CS for the converter:

public class ReadOnlyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value != null)
        {
            var prop = value.GetType().GetProperty(parameter as string);
            if (prop != null)
                return true;
        }
        return false;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

And, just to be complete, this is what I used to setup the data for the screenshot:

public List<IReports> ReportsTable { get; set; }

public MainWindow()
{
    InitializeComponent();
    ReportsTable = new List<IReports>() {
        new Students() { Name = "Student 1" },
        new Students() { Name = "Student 2" },
        new Classes() { ClassName="CS 101", StudentName = "Student 3" },
        new Cars() { CarType = "Truck", Mileage=12345, StudentName = "Student 4" }
    };
    this.DataContext = this;
}

Screenshot:

Answer 4

You could abuse IValueConverter for that. Create one for each column.
In the ValueConverter you can test for the type and return the correct property. An example of what I mean:

public class NameValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is Students)
        {
            return (value as Students).Name;
        }
        if (value is Classes)
        {
            return (value as Classes).ClassName;
        }
        if (value is Cars)
        {
            return (value as Cars).CarType;
        }
        return "";
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

To use it add it as resource to the DataGrid:

<DataGrid.Resources>
    <local:NameValueConverter x:Key="NameValueConverter"></local:NameValueConverter>
</DataGrid.Resources>

And specify it in the binding like this:

{Binding Path=., Converter={StaticResource NameValueConverter}}

This solution would only work for read-only DataGrids though (editing throws a NotImplementedException).