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Using EventHandler with NavigationService

I programming a WPF GUI that uses multiple Views. I am using the MVVM Light Toolkit to implement the MVVM pattern.
For Navigating i use this mechanism by changing my main frame to a NavigationWindow and all my views to Pages.
I injected the navigation service in the ViewModel constructor and now I can navigate between the views.
However, i would like to transmit data between the views while navigating. There is a method from Navigation Window that makes this possible through event handlers. I already implemented a method into my Interface but I'm having problems calling the event handler on the navigated View Model.
Can anyone tell me how to call the event handler inside my ViewModel?
Thanks!!
Edit: I tried calling:
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
}
But i get an error saying:
OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs)': no
suitable method found to override
I already cleaned my solution and tried a rebuild...
Any ideas?
Edit2:
So i found out that in WPF .Net 4.5 the OnNavigatedTo event is gone. What i couldnt find out why and how i could call something similiar.

I haven't gotten an answer to my question so I will attempt an answer...
Don't over think this...if one needs to transfer information either create a static link to the VM(s) in question, or set aside a static drop on the app class. Either way when a view is shown, subscribe to one of the initialization/load events and pick up the information at the predetermined location.

MVVM: How to call method on view from view model?

I am quite new to MVVM, so sorry for probably simple question. However, I can not understand which mechanism from MVVVM (I am using MVVMLight if that is of any consequence) to use in order to program the simple following scenario:
I have textbox TB, where user can fill in URL. Than I have a button B and webview WV. If user clicks on button, the app should take the text from TB and display it in the WV.
I knwo that I can create a property in viewmodel and bound it to TB.Text. I understand probably also that I should create command which will be boudn from button B, but what should I do in the command. How I can call WV.navigate(url), when I do not have reference to WV. Should this be solved by something, which I did not grasp correctly like behaviours? What is the best way to do this?

You should use the messenger pattern for this problem:
http://msdn.microsoft.com/en-us/magazine/dn745866.aspx
http://www.codeproject.com/Tips/696340/Thinking-in-MVVMLight-Messenger
http://mytoolkit.codeplex.com/wikipage?title=Messenger
The idea is that the view can register for specific message classes (in this case for example an own NavigateToUriMessage class) and the view model can send an instance of this message class to whoever listens to the message type. In the command implementation you simply send this message, the view receives the message and changes the URI of the web view.
BTW: The idea of this messenger pattern is that you can better write Unit Tests and use the view model for other platforms (where the reaction to the message may differ).

Another way is to create an attached property for the WebView class where you can bind an Uri property to. The attached property calls Navigate when the bound value changes.
Check out this blog:
http://blogs.msdn.com/b/wsdevsol/archive/2013/09/26/binding-html-to-a-webview-with-attached-properties.aspx

C# WPF userControl to send data to mainWindow textBlock on buttonClick

I am trying to create a simple onscreen keypad created using buttons (currently a User-control), on those buttons i have a click event, when i click/touch a button i want the value of that button sent to a Text-block in my Main-window.
I can't/don't understand how to make the User-control (keypad) see the Text-block (in Main-window) to add in the value that i need.
I have seen solutions that use command Bindings and solutions that use the visual tree traversing but all of them are the main window accessing the user control, not the other way around.

All the examples are the other way around because that is how a UserControl is supposed to work.
A UserControl is a packaged piece of re-usable functionality. It should not know anything about the code that is using it.
Instead you should expose routed events in your UserControl for things like a when number was selected, and subscribe to them in your main window.

There are many ways to achieve what you want. If your MainWindow.xaml has a UserControl and you want to react to a change from the control in the MainWindow.xaml.cs file, then you could add a delegate to the UserControl code behind and register a handler for it in the MainWindow.xaml.cs file. Implementing new delegates are generally somewhat simpler than implementing RoutedEvents, which is another way that you could handle this situation.
Using a delegate like this will enable you to effectively pass a signal to the main view from the child UserControl code behind, which you can react to in any way you want to. Rather than explain the whole story again here, please see my answers from the Passing parameters between viewmodels and How to call functions in a main view model from other view models? posts here on Stack Overflow for full details on how to achieve this.

Access Pivot Control from App.xaml.cs

In my MainPage.xaml, I created a Pivot Control: <controls:Pivot Title="Powder God" Name="PivotControl">.
My first pivot view is a HubTile that summarize all other individual pages. So my application bar will be different between the first pivot view and all other ones.
That's why I put my application bar in App.xaml's resource section, then load based on selected index of my pivot.
My question is:
In the application bar I will be using for all individual pages, I want to have a delete option, where I will remove that specific item (a view model) from my data context.
I know I can use PhoneApplicationFrame root = Application.Current.RootVisual as PhoneApplicationFrame; to access navigation services, but I don't know how can I reference to my pivot, so that I can get the selected index and proceed forward.
Thanks!

Using MVVM you SHOULDN'T do this:
((PageType)Application.Current.RootVisual).PivotControl. //Blah
PageType is whatever type PhoneApplicationFrame is that contains your PivotControl. If this doesn't work you need a Property in the RootVisual
PAGE
public Pivot MyPivot
{
get
{
return PivotControl;
}
}
APP
((PageType)RootVisual).MyPivot. //Blah

On one level Microsoft's suggestion of putting the ApplicationBar in App.xaml is great as it can be referenced from everywhere and would appear to encourage code reuse: however this question highlights the limit to this approach. An application bar is typically used to provide actions which are specific to the current page (or pivot item) and just because the buttons are the same you may not want the exact same code to run in each case.
In this case I think it would better to create a factory method that creates your common ApplicationBar with the click handlers you specify specific to your page/pivot item. For bonus points put the method in a new class (not App) so it doesn't get lost in all the boilerplate code there. Call this factory method in your page constructor and remember your ApplicationBar in your class. For multiple app bars, create them all up front and you can then easily switch between these app bars in your Pivot SelectionChanged code.
The alternative of creating the ApplicationBar in App.xaml and then retrieving this from the App.xaml.cs "Resources" ResourceDictionary in code, modifying the click callbacks, is more complicated in my opinion.
I wish they'd done a better job of implementing the ApplicationBar so people wouldn't want to do this. I've found that using the ApplicationBar forces you to add code to your Page.xaml.cs even if you use a framework like MVVM Light. This is still OK in MVVM as it's UI specific code that belongs in the View, but it makes things inconsistent if you're using ICommand everywhere else. Last time I decided it was better to create the entire ApplicationBar in code rather than hack this kind of thing via App.xaml.cs.
Update: There is a UserVoice request for a data bindable ApplicationBar.

Childwindows in MVVM

I'm having a problem understanding something about MVVM. My application relies on dialogs for certain things. The question is, where should these childwindows originate from? According to MVVM, viewmodels should contain only businesslogic and have zero actual knowledge about UI. However, what other place should I call my childwindows from, considering they're UI elements?
Doesn't this create tight coupling between elements?

Since you tagged the question with Prism, I'll suggest the way I've done it in the past using Prism. Have the IEventAggregator injected into your ViewModel, and then when you want to pop open the dialog, publish a "ShowDialogEvent" or something like that. Then, have another Module called "DialogModule" or whatever, which upon initialization subscribes to that event, and shows the dialog. Furthermore, if you want to pass data back to the original ViewModel, have the ViewModel of the dialog publish a "DialogCloseEvent" or something like that with a payload of the data you need. You can then subscribe to that event back in your main ViewModel.

See Handling Dialogs in WPF with MVVM

In the past, I have accomplished this by using Unity to resolve a custom interface that has a Show() method and a completed event. Then in the ViewModel I would call IScreen screen = container.Resolve<IScreen>(Resources.EditorWindowKey); and then just call screen.Show();.
The big advantage of this is that I can then just simply change my Unity configuration to remove the view when I'm testing my VM's.

The primary route I've been using to do this is to create a command inside your View layer. That command object accepts a parameter that is the ViewModel object that you want to display. The command then finds the appropriate ChildWindow, creates it and displays it with the parameter set as the content or however you will set it up. This way you can just bind a button's command property to that command, and its commandparameter to the object you want to show in the popup and your ViewModel objects never have to care how it's being displayed.
Prompting for user input (like saving a dirty file or something) doesn't work in this scheme. But for simple popups where you manipulate some data and then move on, this works very well.

The ViewModel sample application of the WPF Application Framework (WAF) demonstrates how to show a Modal Dialog.

I would suggest to use a controller in this scenario, say DI'ed dialogController backed up with a dialog shell. The source viewmodel(ie from where the request to open a dialog is originating) will make a call to dialogController.ShowDialog(<<ViewNameToHostInRegion>>,<<RegionName>>).
In Order to transfer the data to and from the dialog and sourceview you can use MessageBus. So essentially when you invoke the ShowDialog() you populate the messagebus, and when the close command of target View(The view hosted in Dialog shell) invoked - say in "Select" button -- Let the target view add/update the messagebus. So that source view model can work with updated data.
It has got many advantages :
1) Your source view works with dialog controller as BlackBox. ie it doesnt aware of what exactly the Dialog view is doing.
2) The view is being hosted in Dialog Shell -- so you can reuse the dialog again and again
3) Unit testing of source view is limited to test the actual functionality of the current viewmodel, and not to test the dialog view\view model.
One heads-up which I came across with this one is, while creating the test cases you may need to write testable Dialog controller which do not show the actual dialog while running the testcases in bunch. So you will need to write a TestableDialogController in which ShowDialog does nothing (Apart from deriving from IDialogController and provide blank implementation of ShowDialog().
Following is the psudeo code :
LocalMessageBus.AddMessage(<MessageKey>,<MessageActualContentAsObject>);
dialogController.ShowDialog(<TargetViewName_SayEmployeeList>);
Employee selectedEmployee = LocalMessageBus.GetMessage(<MessageKey>) as Employee;
if (selectedEmployee != null)
{
//doSomework with selected employee
}