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DependencyProperty does not work if the value is from a binding

I created UserControl with viewmodel. It has DependencyProperty which only works if the value is passed directly. If the value is passed through the binding, it no longer works.
Here is the view code:
This is a closed element not associated with any other. All listed items belong to him. This is a code shortening, I am not going to present whole, immeasurable structures.
View
public partial class SomeView : UserControl
{
public SomeView()
{
InitializeComponent();
SetBinding(ActiveProperty, new Binding(nameof(SomeViewModel.Active)) { Mode = BindingMode.OneWayToSource });
}
#region ActiveProperty
public static readonly DependencyProperty ActiveProperty = DependencyProperty.Register(nameof(Active), typeof(bool), typeof(VNCBoxView));
public bool Active
{
get { return (bool)GetValue(ActiveProperty); }
set { SetValue(ActiveProperty, value); }
}
}
VievModel
public class SomeViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private bool active;
public bool Active
{
get { return active; }
set
{
active = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Active)));
}
}
}
UserControl
<UserControl ...>
<UserControl.DataContext>
<viewModels:SomeViewModel />
</UserControl.DataContext>
<Grid>
<TextBlock Text="{Binding Active}" />
</Grid>
</UserControl>
===================================================
When working with a ready component, which is an individual, separate entity, the problem occurs depending on how it is used.
I remind you that the elements used in the view in question are a closed whole that does not connect with the element in which it is used. It is the transfer of value that is the matter of the problem.
This is working usage:
<local:SomeView Active="True" />
In viewmodel, the setter is invoked twice, once with false and then with true.
If the value comes from binding, it doesn't work:
<local:SomeView Active="{Binding SomeParentProperty}" />
In viewmodel, setter is only called once with the value false.
Setters in a view are never called, in both cases.
Please help

There is no IsConnected property in the SomeViewModel instance in the current DataContext of the UserControl, hence the Binding
<local:SomeView Active="{Binding IsConnected}" />
won't work. It tries to resolve the PropertyPath against the current DataContext, unless you explicitly specify its Source, RelativeSource or ElementName.
This is the exact reason why UserControls should never explicitly set their own DataContext, and hence never have something like an own, private view model.
The elements in the UserControl's XAML would not bind to properties of such a private view model object, but directly to the properties of the UserControl, for example like
<TextBlock Text="{Binding Active,
RelativeSource={RelativeSource AncestorType=UserControl}}"/>

When you set the DataContext explicitly in the UserControl like this:
<UserControl.DataContext>
<viewModels:SomeViewModel />
</UserControl.DataContext>
...you can no longer bind to SomeView's DataContext in the consuming view like this:
<local:SomeView Active="{Binding IsConnected}" />
...because SomeViewModel doesn't have any IsConnected property.
You should avoid setting the DataContext explicitly and let the UserControl inherit its DataContext from its parent element. You can still bind to the dependency property of the UserControl itself using a RelativeSource or an ElementName:
<UserControl ...>
<Grid>
<TextBlock Text="{Binding Active, RelativeSource={RelativeSource AncestorType=UserControl}}" />
</Grid>
</UserControl>
Besides, SomeViewModel seems superfluous in your example since the UserControl already has an Active property.

Set the DataContext of a View on a Navigation in XAML/WPF using MVVM

in my WPF-application i have multiple Views in a main window and i tried to implement a navigation between those.
My Problem is that i can't set the DataContext attribute of the views.
My MainWindowViewModel:
public Class MainWindowViewModel
{
public MainScreenViewModel mainScreenViewModel { get; set; }
public LevelViewModel levelViewModel { get; set; }
public ViewModelBase CurrentViewModel
{
get { return _currentViewModel; }
set
{
_currentViewModel = value;
RaisePropertyChanged(nameof(CurrentViewModel));
}
}
private AdvancedViewModelBase _currentViewModel;
}
My MainWindow:
<Window.Resources>
<DataTemplate DataType="{x:Type ViewModels:MainScreenViewModel}">
<views:MainScreen />
</DataTemplate>
<DataTemplate DataType="{x:Type ViewModels:LevelViewModel}">
<views:LevelView />
</DataTemplate>
</Window.Resources>
<Border>
<StackPanel>
<UserControl Content="{Binding Path=CurrentViewModel, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"></UserControl>
</StackPanel>
</Border>
So the main idea is that the CurentViewModel shows on which View the navigation is at the moment (the DataTemplate shows the coreponding View to the ViewModel).
The Problem is that the shown View doesn't get the DataContext (so the properties mainScreenViewModel/levelViewModel of the MainWindowViewModel), it creates a new instance of the ViewModels.
Is it possible to hand over the properties as a DataContext to the View from the DataTemplate?
Thanks for your help!

The Content property contains
An object that contains the control's content
This means it is not the correct property to bind the view model. Instead you need to bind it to the DataContext property which contains
The object to use as data context
Now the defined templates are selected by their type like defined in the resources.
This means your code is almost correct, just change the binding of the CurrentViewModel like
<UserControl DataContext="{Binding CurrentViewModel}"/>
to get your code to work.

MVVM Basic ContentControl Binding

I'm trying to figure out the correct way to bind a ViewModel to a ContentControl (I've looked all over the net but can't find an example that I can get to work correctly).
My Model:
public class Model
{
private string _Variable = "TEST";
public string Variable
{
get { return _Variable; }
set { _Variable = value; }
}
}
My ViewModel
public class ViewModel :ViewModelBase
{
private Model _Model = new Model();
public string Variable
{
get { return _Model.Variable; }
set
{
if (_Model.Variable != value)
{
_Model.Variable = value;
RaisePropertyChanged("Variable");
}
}
}
My View/Window
<Window.DataContext>
<local:ViewModel />
</Window.DataContext>
<Window.Resources>
<DataTemplate DataType="{x:Type System:String}">
<TextBox/>
</DataTemplate>
</Window.Resources>
<StackPanel>
<ContentControl Content="{Binding Path=Variable}" />
</StackPanel>
So in essence, I have (or at least I believe I have) set the content of the ContentControl to the ViewModel property 'Variable', it is of type string so the only DataTemplate should be implemented and a Textbox displayed.
And that happens... A Textbox is displayed! However the Textbox is empty, and any changes made do not impact Variable.
This means I have made an error in the Batabinding, but I don't understand where. I have a feeling that just because my DataTemplate is displaying a Textbox, nothing is actually binding the string to it, but that is the bit I'm lost over.
Thanks for any help/advice.

You haven't specified the TextBox's Text binding, which is completely separate to the DataContext. Since you want the TextBox to bind to its own DataContext just do this:
<TextBox Text="{Binding Path=.}"/>

use textbox as below:
<TextBox Text="{Binding}" />

Can/Should I create instances of a UserControl in my viewmodel?

Question regarding UserControls and MVVM. I have my wpf app with a main View/ViewModel. The viewmodel has a ObservableCollection of my usercontrol(s) that a listbox is bound to. The UserControl instances are added to the collection at run time based on events.
My question is if it's within the MVVM pattern to create the usercontrol objects from my main viewmodel? Example below in the onSomeEvent method is the code I'm unsure of, if this is where I should handle it? This doesn't feel right to me, but I'm still wrapping my mind around mvvm. Should I be adding the user control viewmodel here instead? Thanks for any guidance.
private ObservableCollection<string> myList = new ObservableCollection<string>();
public ObservableCollection<string> MyList
{
get { return myList; }
set
{
myList = value;
RaisePropertyChangedEvent("MyList");
}
}
public void onSomeEvent(string someData1, string someData2)
{
this.MyList.Add(new Views.MyUserControl(someData1, someData2));
}
Ok, I mocked up some code based on feedback from BradleyDotNET and dymanoid as I wrap my mind around it. Pasting it here to see if I'm on the right track.
I modified the listbox in my mainview xaml to add a template:
<ListBox Name="lbMain" Margin="10" ItemsSource="{Binding MyList, Mode=TwoWay}">
<ListBox.ItemTemplate>
<DataTemplate>
<WrapPanel>
<TextBlock Text="{Binding Test1}" FontWeight="Bold" />
<TextBlock Text="{Binding Test2}" FontWeight="Bold" />
</WrapPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I then created a simple class like this to populate a few fields.
public class MyData
{
public MyData(string test1, string test2)
{
this.Test1 = test1;
this.Test2 = test2;
}
private string test1;
public string Test1
{
get
{
return test1;
}
set
{
test1 = value;
}
}
private string test2;
public string Test2
{
get
{
return test2;
}
set
{
test2 = value;
}
}
}
Then in my mainviewmodel I did this:
public void onSomeEvent(string someData1, string someData2)
{
this.MyList.Add(new MyData(someData1, someData2));
}

No, your viewmodel should not create any UserControl instances, because they are views. Furthermore, your main viewmodel shouldn't contain any collections of any views. As #BradleyDotNET mentioned, DataTemplate is the right way for it.
You should change your main viewmodel collection. It shouldn't contain any UserControls (views), but rather their viewmodels. Assuming that you have defined DataTemplates for your sub-viewmodels in XAML, you will get your views automagically created by WPF.
This could look like:
<DataTemplate DataType = "{x:Type local:UserControlViewModel}">
<local:UserControl/>
</DataTemplate>
With this approach, WPF sets the DataContext property value to the sub-viewmodel instance automatically, so you can easily define your bindings in that UserControl.

WPF ComboBox Binding To Object On Initial Load

I have a combo box that is bound to a list of model objects. I've bound the combo box SelectedItem to a property that is the model type. All of my data binding works beautifully after the window has been loaded. The SelectedItem is set properly and I'm able to save the object directly with the repository.
The problem is when the window first loads I initialize the SelectedItem property and my combobox displays nothing. Before I moved to binding to objects I was binding to a list of strings and that worked just fine on initialization. I know I'm missing something but I can't figure it out.
Thanks in advance for any guidance you can provide.
(One note about the layout of this page. The combo boxes are actually part of another ItemTemplate that is used in a ListView. The ListView is bound to an observable collection in the main MV. Each item of this observable collection is itself a ModelView. It is that second ModelView that has the SelectedItem property.)
Here is my Model:
public class DistributionListModel : Notifier, IComparable
{
private string m_code;
private string m_description;
public string Code
{
get { return m_code; }
set { m_code = value; OnPropertyChanged("Code"); }
}
public string Name
{
get { return m_description; }
set { m_description = value; OnPropertyChanged("Name"); }
}
#region IComparable Members
public int CompareTo(object obj)
{
DistributionListModel compareObj = obj as DistributionListModel;
if (compareObj == null)
return 1;
return Code.CompareTo(compareObj.Code);
}
#endregion
}
Here the pertinent code in my ModelView:
public MailRoutingConfigurationViewModel(int agencyID)
: base()
{
m_agencyID = agencyID;
m_agencyName = DataManager.QueryEngine.GetAgencyName(agencyID);
IntializeValuesFromConfiguration(DataManager.MailQueryEngine.GetMailRoutingConfiguration(agencyID));
// reset modified flag
m_modified = false;
}
private void IntializeValuesFromConfiguration(RecordCheckMailRoutingConfiguration configuration)
{
SelectedDistributionList = ConfigurationRepository.Instance.GetDistributionListByCode(configuration.DistributionCode);
}
public DistributionListModel SelectedDistributionList
{
get { return m_selectedDistributionList; }
set
{
m_selectedDistributionList = value;
m_modified = true;
OnPropertyChanged("SelectedDistributionList");
}
}
And finally the pertinent XAML:
<UserControl.Resources>
<DataTemplate x:Key="DistributionListTemplate">
<Label Content="{Binding Path=Name}" />
</DataTemplate>
</UserControl.Resources>
<ComboBox
ItemsSource="{Binding Source={StaticResource DistributionCodeViewSource}, Mode=OneWay}"
ItemTemplate="{StaticResource DistributionListTemplate}"
SelectedItem="{Binding Path=SelectedDistributionList, Mode=TwoWay}"
IsSynchronizedWithCurrentItem="False"
/>

#SRM, if I understand correctly your problem is binding your comboBox to a collection of objects rather than a collection of values types ( like string or int- although string is not value type).
I would suggest add a two more properties on your combobox
<ComboBox
ItemsSource="{Binding Source={StaticResource DistributionCodeViewSource},
Mode=OneWay}"
ItemTemplate="{StaticResource DistributionListTemplate}"
SelectedItem="{Binding Path=SelectedDistributionList, Mode=TwoWay}"
SelectedValuePath="Code"
SelectedValue="{Binding SelectedDistributionList.Code }"/>
I am assuming here that DistributionListModel objects are identified by their Code.
The two properties I added SelectedValuePath and SelectedValue help the combobox identify what properties to use to mark select the ComboBoxItem by the popup control inside the combobox.
SelectedValuePath is used by the ItemSource and SelectedValue by for the TextBox.

don't call your IntializeValuesFromConfiguration from the constructor, but after the load of the view.
A way to achieve that is to create a command in your viewmodel that run this method, and then call the command in the loaded event.
With MVVM light toolkit, you can use the EventToCommand behavior... don't know mvvm framework you are using but there would probably be something like this.