NavigationService.Navigate error

Question

I'm quite new on C# programming and I have a problem on my code. I have created a button and applied on it an event click which open an other page of my project by the technology NavigationService.

This is the script:

private void click_login(object sender, RoutedEventArgs e)
{
    NavigationService nav = NavigationService.GetNavigationService(this); 
    nav.Navigate(new Uri("Window1.xaml", UriKind.RelativeOrAbsolute));
}

When I execute, I get this error:

The object reference is not set to an instance of an object with an InnerException null.

Can you help me please?

did you checked if nav is not null when your debugging this ? and here a some Remarks when [GetNavigationService returns null](http://msdn.microsoft.com/en-US/library/system.windows.navigation.navigationservice.getnavigationservice(v=vs.110).aspx) — Mark, Aug 11 '14 at 07:26
You have seen right, nav in null. Do I have to initiate with "new"? — Kraenys, Aug 11 '14 at 07:48
No, please check the link i've provided in the remarks section there is a description when the GetNavigationService-Method returns null. There's probably something wrong with the `this` you are handing over to the method. — Mark, Aug 11 '14 at 08:18
This returns 2 things: WpfApplication3.MainWindow which only have "InitializeComponent();" for the moment and the second thing is my button in mainwindow.xaml Is that mean there's a conflict about what "this" mean? — Kraenys, Aug 11 '14 at 08:39
Indeed, it's Window. Like this: public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); } — Kraenys, Aug 11 '14 at 09:01

score 4 · Accepted Answer · answered Aug 11 '14 at 09:05

4

Your nav object is null, because you're trying to get the NavigationService for a WPF Window.

But for Navigation you need a Page (Navigation Overview on MSDN)

A Little Working example:

Create to Page's Page1.xaml, Page2.xaml

In the App.xaml change the StartupUri to StartupUri="Page1.xaml"

Page1 Xaml:

 <StackPanel>
     <TextBlock Text="Hello from  Page1" />
     <Button Click="Button_Click" Content="Navigate to page 2"></Button>
 </StackPanel>

Page1 cs:

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        NavigationService nav = NavigationService.GetNavigationService(this);
        nav.Navigate(new Uri("Page2.xaml", UriKind.RelativeOrAbsolute));
    }

Page2 Xaml:

 <StackPanel>
     <TextBlock Text="Hello from  Page2" />
     <Button Click="Button_Click" Content="Navigate to page 1"></Button>
 </StackPanel>

Page2 cs:

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        NavigationService nav = NavigationService.GetNavigationService(this);
        nav.Navigate(new Uri("Page1.xaml", UriKind.RelativeOrAbsolute));
    }

answered Aug 11 '14 at 09:05

Mark

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Sorry for my late, i come back from eat. If i understand what you say, it's because i have created a window and not a page that i have a problem. I create a new project and try your codes, i come to you quickly to tell you what happen. Thank you for your answer – Kraenys Aug 11 '14 at 10:53
Okay there it's works. Now i try to understand why. On my project, i want to navigate from a window, my main window to an other window, window1 I have tried to navigate from my main window to a page called Page1.xaml, same error. Have I to create an other page, containing the xaml code of the main window and redirecting the StartupUri to this page. (in order to get a page to page navigation?) – Kraenys Aug 11 '14 at 10:58
Okay now it works for my project. I have created a main page instead of a main window. Now i can navigate from the interface to the login by clicking on the button. I just have a last button, how can i call the next page like a pop-up and not like an other page? Thanks in advance. – Kraenys Aug 11 '14 at 11:05
With the NavigationService you can't navigate between Windows that's what the Page is for. If you want to have a popup the Navigation Service is not what you are looking for. There are several different ways how to open popups or dialogs in WPF for example [Window.ShowDialog](http://msdn.microsoft.com/en-us/library/system.windows.window.showdialog(v=vs.110).aspx) or [Popup Control](http://msdn.microsoft.com/en-us/library/system.windows.controls.primitives.popup(v=vs.110).aspx) – Mark Aug 11 '14 at 11:31

NavigationService.Navigate error

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