Android splash screen for UNO UWP project

Question

I am trying to implement an splash screen for the Android part of my UNO solution. I can get the splash screen to appear, wait a few seconds but upon navigation to the main page I get the following exception in the app.cs

protected override void OnLaunched(LaunchActivatedEventArgs e)
{
#if DEBUG
    if (System.Diagnostics.Debugger.IsAttached)
    {
       // this.DebugSettings.EnableFrameRateCounter = true;
    }
 #endif
    Frame rootFrame = Windows.UI.Xaml.Window.Current.Content as Frame;

    // Do not repeat app initialization when the Window already has content,
    // just ensure that the window is active
    if (rootFrame == null)
    {
      // Create a Frame to act as the navigation context and navigate to the first page
           rootFrame = new Frame(); <<<<< exception

Unhandled Exception: Java.Lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference occurred

The stack trace is as simple as :

0x25 in Uno1.App.OnLaunched at C:\Users\pjsta\Documents\Visual Studio 2017\Projects\Uno1\Uno1\Uno1.Shared\App.xaml.cs:55,17 C#

The relevant part of the solution are 1. my new SplashActivity in the Android project

 [Activity(Label = "SplashScreen", MainLauncher = true, Theme = "@style/Theme.SplashActivity")]

   public class SplashActivity : Activity
   {
        protected override void OnCreate(Bundle savedInstanceState)
        {
             base.OnCreate(savedInstanceState); 
             System.Threading.Thread.Sleep(1000);
             StartActivity(typeof(MainActivity));
        }
    }

2. Modification to MainActivity to not be the MainLauncher

   [Activity( MainLauncher = false, ConfigurationChanges = ConfigChanges.Orientation | ConfigChanges.ScreenSize, WindowSoftInputMode = SoftInput.AdjustPan | SoftInput.StateHidden )]

   public class MainActivity : Windows.UI.Xaml.ApplicationActivity { }

The relevant style loads fo the splash screen OK. Switching the MainActivity back to MainLauncher=true works , albeit without a splash screen. I am a newbie to Xamarin and Android development, but competent in UWP. Anyone out there got any ideas?

Answer 1

From the exception, it sounds like when new Frame() is called, the base native constructor is called with a null Context. This is probably because Uno expects ApplicationActivity to be run as MainLauncher=true. It's possible that inheriting your SplashActivity class from Uno.UI.BaseActivity could resolve the error.

A better way to show a splash screen on Android is to modify the theme rather than create a separate activity. I'll use the Uno Gallery app as an example.

1. Create a file in the Resources/drawable folder of your Android head called, eg, splash.xml. Define your splash screen visual appearance here.

2. Open the Resources/values/Styles.xml file. Inside the 'AppTheme' style add the following line:

   <item name="android:windowBackground">@drawable/splash</item>
   

Hope that helps. Also, please tag questions about the Uno Platform as 'uno-platform' (the 'uno' tag refers to the OpenOffice component model).