How to create a Dependency Property for Binding

Question

I'm working on a "simple" case. I like to create a new custom control which implements a DependencyProperty. In the next step I like to create a binding for updating the properties in both directions. I've builded a simple sample for this case, but the binding doesn't seem to work. I've found a way for updating the DPControl's property by using the FrameworkPropertyMetadata, but I don't know whether it's also a good idea to use the OnPropertyChanged event.

HERE is my sample project:

My control contains simply a Label

<UserControl x:Class="WPF_MVVM_ListBoxMultiSelection.DPControl" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:local="clr-namespace:WPF_MVVM_ListBoxMultiSelection" mc:Ignorable="d" Height="84.062" Width="159.641"> <Grid Margin="0,0,229,268"> <Label Content="TEST" x:Name="label" Margin="0,0,-221,-102"/> </Grid> </UserControl>

and implement a custom dependency property. Currently, I have also implemented the PropertyChanged method for the FramePropertyMetadata and set in this method the label's content, but I like to get it work in both directions.

public partial class DPControl : UserControl { public DPControl() { InitializeComponent(); } public string MyCustomLabelContent { get { return (string)GetValue(MyCustomLabelContentProperty);} set { SetValue(MyCustomLabelContentProperty, value); } } private static void OnMyCustomLabelContentPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e) { DPControl control = (DPControl)source; control.label.Content = e.NewValue; } public static readonly DependencyProperty MyCustomLabelContentProperty = DependencyProperty.Register( "MyCustomLabelContent", typeof(string), typeof(DPControl), new FrameworkPropertyMetadata(null, OnMyCustomLabelContentPropertyChanged ) );

I use this control simply in a Window by:

<local:DPControl MyCustomLabelContent="{Binding MyLabelContent, Mode=TwoWay}" Margin="72,201,286,34"/>

MyLabelContent is a property in the ViewModel, which has implemented also the INotifyPropertyChanged interface.

public class ViewModel_MainWindow:NotifyPropertyChanged { private string _myLabelContent; public string MyLabelContent { get { return _myLabelContent; } set { _myLabelContent = value; RaisePropertyChanged(); } }...

So how can I get it work: Using the binding feature with my new control on custom properties.

15ee8f99-57ff-4f92-890c-b56153 · Accepted Answer · 2017-06-06 15:15:16Z

In your UserControl:

<Label Content="{Binding MyCustomLabelContent, RelativeSource={RelativeSource AncestorType=UserControl}}" x:Name="label" Margin="0,0,-221,-102"/>

And get rid of that property-changed callback. All you need is the Binding.

I like to get it work in both directions

To make the dependency property two-way by default:

public static readonly DependencyProperty MyCustomLabelContentProperty = DependencyProperty.Register( "MyCustomLabelContent", typeof(string), typeof(DPControl), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault) );

I omitted the unnecessary property change handler.

It can't usefully be two-way now, because Label.Content can't generate its own value. If you want your UserControl to set the value in its codebehind, that's easy:

MyCustomLabelContent = "Some arbitrary value";

If you did the binding like I showed you, that will update the Label in the UserControl XAML as well as the viewmodel property bound to the UserControl's dependency property.

If you want the XAML to set it, you'll need to

Lastly, this:

Margin="0,0,-221,-102"

Is not a good way to do layout. WPF layout with Grid, StackPanel, etc. is much easier and more robust.

Thanks, this works for the simple case, but now I like to implement like a wrapper-usercontrol for the listbox for getting the ItemsSelected, but it doesn't work. Any hints on this case?
@Kinimod ItemsSelected is a pain: you can't bind it. Also it's a collection, so you have to handle change notifications. That's another question.
you're right it's a pain. Any suggestion for another third party control handling lists like with a listbox, which has a SelectedItems list for binding?
@Kinimod The only third party WPF controls I've dealt with are DevExpress and Infragistics and I didn't much care for either one. I think there's an attached property/behavior in an answer around here somewhere that will let you bind SelectedItems. I might have something like that around somewhere.

Collectives™ on Stack Overflow

How to create a Dependency Property for Binding

1 Answer 1

4 Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Related