Binding viewmodel to view has usercontrol with own viewmodel

Question

I have a UserControl 'UserControlA' with ViewModel 'ViewModelA'. 'UserControlA' has 'UserControlB', and 'UserControlB' has 'ViewModelB'.

When I bind a DependencyProperty in 'UserControlA' with 'ViewModelA' property, there is none of setter fired.

Belows are code,

ViewA.xaml

<UserControl 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:vm="clr-namespace:MyTest.ViewModel xmlns:custom="clr-namespace:MyTest.Views x:Name="userControl" x:Class="MyTest.Views.UserControlA" mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="500"> <UserControl.DataContext> <vm:UserViewModel x:Name="uvModel"/> </UserControl.DataContext> <Grid> <custom:UserControlB></custom:UserControlB>

ViewA.cs

public partial class UserView : UserControl, IUserView { static DependencyProperty UserTypeProperty = DependencyProperty.Register("UserType", typeof(UserType), typeof(UserView), new PropertyMetadata(UserType.None)); public UserType UserType { get { return (UserType)GetValue(UserTypeProperty); } set { SetValue(UserTypeProperty, value); } } public ViewA() { InitializeComponent(); Binding typeBinding = new Binding(); typeBinding.Source = this.DataContext; typeBinding.Path = new PropertyPath("User.UserType"); typeBinding.Mode = BindingMode.OneWayToSource; this.SetBinding(UserTypeProperty, typeBinding); }

ViewModelA.cs

public class ViewModelA : ViewModelBase { User user = new User(); public User User { get { return this.user; } set { this.user = value; RaisePropertyChanged(() => User); } }

Please help me out from this problem.

There appears to be a bunch of wrong in here, but not sure if caused by editing the question down. Your DP definition is lacking getters/setters, you claim has usercontrol with own viewmodel yet I don't see that (horrible code smell) in your code, and I can't tell if your ViewModelA has a public property ViewModelB, which it should if your UserControlB is nested in your ViewModelA. — user1228
– user1228, Commented Nov 2, 2016 at 14:40

Clemens · Accepted Answer · 2016-11-02 08:42:23Z

The line

typeBinding.Source = this.DataContext;

is redundant, because the DataContext is implicitly used as source object of the Binding.

However, during the execution of the UserControl's constructor the DataContext property is not yet set (i.e. it is null), so you are effectively setting the Binding's Source property to null. Just remove that line, or write

SetBinding(UserTypeProperty, new Binding { Path = new PropertyPath("User.UserType"), Mode = BindingMode.OneWayToSource });

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