in a wpf project,How to add code in to the App's InitializeComponent method

To execute a function at startup, add this attribute to App.xaml:

<Application 
   . . . 
   Startup="Application_Startup">
    
</Application>

Then define the function in App.xaml.cs:

public partial class App : Application
{
    private void Application_Startup( object sender, StartupEventArgs e )
    {
        MessageBox.Show( "Hello!" );
    }
}

Or use the events or constructor of the main window.

The .g.cs and .g.i.cs files are generated and overwritten by system and cannot be edited manually.