WPF, MVVM and application wide resources best practices - wpf

Question

I am currently writing a WPF application which has a navigation panel on its left side (to which I bind a navigationViewModel) and a content presenter on its right side (which I bind to the previously mentioned VM's UserControl member 'CurrentView'.
For each item of this navigation panel, I created a corresponding user control and for each of these user controls, I bind an instance of a corresponding ViewModel.
Clicking on a navigation panel's items sets its ViewModel's UserControl member CurrentView to the instance of the corresponding UC, which is then displayed in the content presenter mentioned above.
The first navigation item is some "select or create a new client" form. When this operation is done, I would like to set some wide app resource id to which I would bind the other navigation items Enabled state. Thus, if the wide app resource is null, they are disabled, as soon as it is set to anything, they are enabled. There would also be some mechanism which would allow the corresponding ViewModel to be notified of this situation.
I am wondering if this would be considered a good practice?
Furthermore, I'd like to know if I can simply declare an int resource in the app.xaml and bind it to the navigation items Enabled property, would setting this resource to anything immediately refresh this property? Or is there a better, simpler or cleaner way?

Answer 1

An alternative could be to nest the two viewmodels (navigation and currentview) in a third viewmodel (say mainviewmodel)
This main viewmodel could then keep state that should be available across these viewmodels and across instances of currentviews.
This way you do not need to have global state in the application and you can simply set the datacontext of the Window to the main viewmodel and bind the navigation and content views to properties of the main viewmodel.
This also allows you to have a proper place for navigating to a different content view.

Answer 2

Here is what I ended up doing:
In my app.xaml; I declare the following resource:
<Application x:Class="MyProject.GUI.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="clr-namespace:MyProject.GUI.ViewModels"
StartupUri="MainWindow.xaml">
<Application.Resources>
<vm:MainViewModel x:Key="MainViewModel" />
</Application.Resources>
</Application>
This MainViewModel exposes a static property as follow:
static bool _myStaticProperty;
public static bool MyStaticProperty
{
get
{
return _myStaticProperty;
}
set
{
_myStaticProperty = value;
NotifyStaticPropertyChanged("MyStaticProperty");
}
}
And the following static INPC mechanism:
#region Static property INPC mechanism
public static event EventHandler<PropertyChangedEventArgs> StaticPropertyChanged;
static void NotifyStaticPropertyChanged(string propertyName)
{
if (StaticPropertyChanged != null)
{
StaticPropertyChanged(null, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
And my different viewmodels:
FirstChildViewModel _firstChildViewModel;
public FirstChildViewModel FirstChildViewModel
{
get
{
if (_firstChildViewModel == null)
_firstChildViewModel = new FirstChildViewModel();
return _firstChildViewModel;
}
}
//then a second one, a third one and so on
Which are binded to my user controls as follow
<UserControl x:Class="MyProject.GUI.Views.FirstChildControl"
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:MyProject.GUI.ViewModels"
mc:Ignorable="d"
DataContext="{Binding Path=FirstChildViewModel,
Source={StaticResource MainViewModel}}">
In my user controls' xaml code, I declare command bindings etc. which basically do the following in their ViewModel
MainViewModel.MyStaticProperty = myBoolValue;