WPF: How to start from a window in a different assembly

This article gives a clean XAML-only solution.

StartupUri="pack://application:,,,/assembly_name;component/path/file_name.xaml"

Where:

• assembly_name is the name of the referenced assembly, sans extension
• path is the subfolder in which the component resides; if the component is at the project root, this element is omitted
• file_name is the file name of the component

Examples:

pack://application:,,,/UI;component/CalculatorView.xamlassembly - UI.dllpath - none (file at project root)file_name - CalculatorViewpack://application:,,,/MyApp.UI;component/Views/CalculatorView.xamlassembly - MyApp.UI.dllpath - Viewsfile_name - CalculatorViewpack://application:,,,/UI;component/Views/External/CalculatorView.xaml assembly - UI.dllpath - Views/Externalfile_name - CalculatorView 

I'd check your pack URI. Below is the uri I'd try. Think of 'component' as the root folder in your project and where I've put 'FolderName' put the appropriate folder name or remove it if Main.xaml is in the root of the project.

StartupUri = new Uri(@"pack://application:,,,/CompanyName.VisualStudio.UI;component/FolderName/Main.xaml", UriKind.Absolute);

Old question, but this is also helpful:

void App_Startup(object sender, StartupEventArgs e)        {            MainWindow = new YourWindow(some, arguments);            MainWindow.Show();}

and i app.xaml:

<Application  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  x:Class="SDKSample.App"  Startup="App_Startup" />

and rememeber about ShutdownMode : if you remember to open new window before closing last one you should be good