DependencyPropertyBehavior

• Jun 07, 2019
• 2 minutes to read

Sometimes, some properties of a UI control are not dependency properties, for instance, the TextBox.SelectedText property. This means the WPF binding system cannot target this property and the code below is not allowed

XAML

<TextBox Text="Select some text in this box" SelectedText="{Binding SelectedText, Mode=TwoWay}"/>

DependencyPropertyBehavior can be used to overcome such issues.

XAML

<TextBox Text="Select some text in this box">
    <dxmvvm:Interaction.Behaviors>
        <dxmvvm:DependencyPropertyBehavior PropertyName="SelectedText" EventName="SelectionChanged" Binding="{Binding SelectedText, Mode=TwoWay}"/>
    </dxmvvm:Interaction.Behaviors>
</TextBox>

To use the DependencyPropertyBehavior, it is necessary to set three its properties:

• PropertyName - specifies the name of a property that should be bound.
• Binding - specifies a binding that should be applied to the specified property.
• EventName - specifies an event which the DependencyPropertyBehavior process to perform updating of the specified binding.

Example

Note

A complete sample project is available at https://github.com/DevExpress-Examples/how-to-use-dependencypropertybehavior-t122997.

MainView.xaml

<UserControl x:Class="Example.View.MainView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:ViewModel="clr-namespace:Example.ViewModel"
    xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d" d:DesignHeight="500" d:DesignWidth="600"
    DataContext="{dxmvvm:ViewModelSource Type=ViewModel:MainViewModel}">


    <Grid x:Name="LayoutRoot" Background="White">
        <StackPanel Orientation="Horizontal" VerticalAlignment="Top">
            <!--The TextBox.SelectedText property is not a dependency property-->
            <TextBox Width="200" Text="Select some text in this box">
                <dxmvvm:Interaction.Behaviors>
                    <dxmvvm:DependencyPropertyBehavior PropertyName="SelectedText" EventName="SelectionChanged" Binding="{Binding SelectedText, Mode=TwoWay}"/>
                </dxmvvm:Interaction.Behaviors>
            </TextBox>
            <TextBox Width="200" Text="{Binding SelectedText}" IsReadOnly="True"/>
        </StackPanel>
    </Grid>
</UserControl>

MainWindow.xaml.vb

Imports System.Windows

Namespace Example
    Partial Public Class MainWindow
        Inherits Window

        Public Sub New()
            InitializeComponent()
        End Sub
    End Class
End Namespace

MainViewModel.vb

Imports DevExpress.Mvvm
Imports DevExpress.Mvvm.DataAnnotations

Namespace Example.ViewModel
    <POCOViewModel> _
    Public Class MainViewModel
        Public Overridable Property SelectedText() As String
    End Class
End Namespace

MainView.xaml.vb

Imports System.Windows.Controls

Namespace Example.View
    Partial Public Class MainView
        Inherits UserControl

        Public Sub New()
            InitializeComponent()
        End Sub
    End Class
End Namespace

MainWindow.xaml

<Window x:Class="Example.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:View="clr-namespace:Example.View"
        Title="MainWindow" Height="600" Width="800">
    <Grid>
        <View:MainView/>
    </Grid>
</Window>

MainView.xaml.cs

using System.Windows.Controls;

namespace Example.View {
    public partial class MainView : UserControl {
        public MainView() {
            InitializeComponent();
        }
    }
}

MainWindow.xaml.cs

using System.Windows;

namespace Example {
    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
        }
    }
}

MainViewModel.cs

using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;

namespace Example.ViewModel {
    [POCOViewModel]
    public class MainViewModel {
        public virtual string SelectedText { get; set; }
    }
}