Binding objects defined in code-behind

Question

I have some object that is instantiated in code behind, for instance, the XAML is called window.xaml and within the window.xaml.cs

protected Dictionary<string, myClass> myDictionary;

How can I bind this object to, for example, a list view, using only XAML markups?

Update:

(This is exactly I have in my test code):

<Window x:Class="QuizBee.Host.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="{Binding windowname}" Height="300" Width="300"
    DataContext="{Binding RelativeSource={RelativeSource Self}}">
    <Grid>
    </Grid>
</Window>

And in codebehind

public partial class Window1 : Window
{
    public const string windowname = "ABCDEFG";

    public Window1()
    {
        InitializeComponent();
    }
}

Suppose the title should become "ABCDEFG" right? but it ends up showing nothing.

Answer 1

There's a much easier way of doing this. You can assign a Name to your Window or UserControl, and then binding by ElementName.

Window1.xaml

<Window x:Class="QuizBee.Host.Window1"
        x:Name="Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <ListView ItemsSource="{Binding ElementName=Window1, Path=myDictionary}" />
</Window>

Window1.xaml.cs

public partial class Window1:Window
{
    // the property must be public, and it must have a getter & setter
    public Dictionary<string, myClass> myDictionary { get; set; }

    public Window1()
    {
        // define the dictionary items in the constructor
        // do the defining BEFORE the InitializeComponent();

        myDictionary = new Dictionary<string, myClass>()
        {
            {"item 1", new myClass(1)},
            {"item 2", new myClass(2)},
            {"item 3", new myClass(3)},
            {"item 4", new myClass(4)},
            {"item 5", new myClass(5)},
        }; 

        InitializeComponent();
    }
}

Answer 2

While Guy's answer is correct (and probably fits 9 out of 10 cases), it's worth noting that if you are attempting to do this from a control that already has its DataContext set further up the stack, you'll resetting this when you set DataContext back to itself:

DataContext="{Binding RelativeSource={RelativeSource Self}}"

This will of course then break your existing bindings.

If this is the case, you should set the RelativeSource on the control you are trying to bind, rather than its parent.

i.e. for binding to a UserControl's properties:

Binding Path=PropertyName, 
        RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}

Given how difficult it can be currently to see what's going on with data binding, it's worth bearing this in mind even if you find that setting RelativeSource={RelativeSource Self} currently works :)

Answer 3

Just a little more clarification: A property without 'get','set' won't be able to be bound

I'm facing the case just like the asker's case. And I must have the following things in order for the bind to work properly:

//(1) Declare a property with 'get','set' in code behind
public partial class my_class:Window {
  public String My_Property { get; set; }
  ...

//(2) Initialise the property in constructor of code behind
public partial class my_class:Window {
  ...
  public my_class() {
     My_Property = "my-string-value";
     InitializeComponent();
  }

//(3) Set data context in window xaml and specify a binding
<Window ...
DataContext="{Binding RelativeSource={RelativeSource Self}}">
  <TextBlock Text="{Binding My_Property}"/>
</Window>

Answer 4

Make your property "windowname" a DependencyProperty and keep the remaining same.

Answer 5

Define a converter:

public class RowIndexConverter : IValueConverter
{
    public object Convert( object value, Type targetType,
                           object parameter, CultureInfo culture )
    {
        var row = (IDictionary<string, object>) value;
        var key = (string) parameter;
        return row.Keys.Contains( key ) ? row[ key ] : null;
    }

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

Bind to a custom definition of a Dictionary. There's lot of overrides that I've omitted, but the indexer is the important one, because it emits the property changed event when the value is changed. This is required for source to target binding.

public class BindableRow : INotifyPropertyChanged, IDictionary<string, object>
{
    private Dictionary<string, object> _data = new Dictionary<string, object>( );

    public object Dummy   // Provides a dummy property for the column to bind to
    {
        get
        {
            return this;
        }
        set
        {
            var o = value;
        }
    }


    public object this[ string index ]
    {
        get
        {
            return _data[ index ];
        }
        set
        {
            _data[ index ] = value;
            InvokePropertyChanged( new PropertyChangedEventArgs( "Dummy" ) ); // Trigger update
        }
    }


}

In your .xaml file use this converter. First reference it:

<UserControl.Resources>
    <ViewModelHelpers:RowIndexConverter x:Key="RowIndexConverter"/>
</UserControl.Resources>

Then, for instance, if your dictionary has an entry where the key is "Name", then to bind to it: use

<TextBlock  Text="{Binding Dummy, Converter={StaticResource RowIndexConverter}, ConverterParameter=Name}">

Answer 6

In your code behind, set the window's DataContext to the dictionary. In your XAML, you can write:

<ListView ItemsSource="{Binding}" />

This will bind the ListView to the dictionary.

For more complex scenarios, this would be a subset of techniques behind the MVVM pattern.