Slow startup of xamarin app

Question

We are developing a cross platform app on a PCL, but for the time being we are only using android devices for testing.
Our concern is that its taking about 6 to 8 seconds (depending on which device we test it) to start the app, which is very slow.
After placing a few breakpoints we saw that the timing is consumed pretty evenly.
We did notice this particular parts took longer:

• 1s before reaching onCreate() on MainActivity (there's a splash screen before which only has one image and a background color)
• 1s on base.OnCreate(bundle);
• 1s on global::Xamarin.Forms.Forms.Init(this, bundle);
• 1.5s on Page mainPage = new LogScreen(); (creating the main page to then set it as main navigation page).

Answer 1

First thing I would recommend is to not benchmark a debug build of your app, the code paths of the Mono runtime and Jit'd code are not the same as a release build, the use of shared runtimes, assembly sizes, etc, etc, etc. will all effect the startup and execution times.

Here are examples of startup times of a "very large" aggressively tuned Android Forms-based app on high-end and low-end devices using an in-house benchmarker (conditionally compiled in, not injected, and using the OS's system clock).

App Overview:

• Xamarin.Forms v2.4.0.269-pre2
• Mix of coded and XAML based Pages, Controls, etc...
• XAML Compiler enabled
• "Splash screen" disabled
  • A Theme-based splash on MainActivity will add:
    • 200+ milliseconds to startup times on a fast device,
    • 1-2 seconds on a device w/ slow flash access
  • Just do not use an Activity-based splash-screen ;-)
• Multi-dex'd
• Proguard'd (aggressively reduced jars via UI testing w/ auto-feedback loop)
• Linker (Link All, aggressively reduced assembly sizes with a custom link description file generated via UI testing w/ auto-feedback)
• 100% source-built to allow collapsing namespaces and assembly reduction
• Viper architecture w/ no 3rd-party DI/IoC
• Lazy-loaded design using data, resource ad network priority queues
• Realm live objects and queries used for all data (DB min. size: 250MB, max. size 1.2GB)

Times are generated via a shell script that reboots the devices, monitors the startup to wait for the system to settle, launches a series of apps (GApps, Facebook, Instagram, Twitter, etc...), waits for the system to settle, and then launches the Forms app via:

export deviceTime=$(echo "$(adb -s $deviceID shell cat /proc/uptime | awk '{print $1}') * 1000" | bc -l)
adb -s $deviceID shell am start -n com.sushihangover.GeneticCancerDNAMapper/com.sushihangover.GeneticCancerDNAMapper.DevOpsDashboard --el startTime ${deviceTime%.*}

Google Pixel (Oreo-based) device (app is usable in ~430ms):

I GeneticCancerDNAMapper: 0.162 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.OnCreate
I GeneticCancerDNAMapper: 0.164 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.base.SetTheme
I GeneticCancerDNAMapper: 0.201 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.base.OnCreate
I GeneticCancerDNAMapper: 0.244 : Xamarin.Forms.Forms.Init
I GeneticCancerDNAMapper: 0.266 : Realms.Realm.GetInstanceAsync ~Get Instance & Data~
I GeneticCancerDNAMapper: 0.324 : Realms.Realm.GetInstanceAsync ~Obtained Instance & Data~
I GeneticCancerDNAMapper: 0.324 : Xamarin.Forms.Application Content
I GeneticCancerDNAMapper: 0.349 : Xamarin.Forms.Application Content ~Creation Completed~
I GeneticCancerDNAMapper: 0.353 : Xamarin.Forms.Application.MainPage ~Displayed~
I GeneticCancerDNAMapper: 0.43 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.LoadApplication

Low-end "Android One" 512MB device w/ very slow flash (app is usable in ~4.5s):

Re: https://en.wikipedia.org/wiki/Android_One

I/GeneticCancerDNAMapper(10904): 2.453 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.OnCreate
I/GeneticCancerDNAMapper(10904): 2.467 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.base.SetTheme
I/GeneticCancerDNAMapper(10904): 2.731 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.base.OnCreate
I/GeneticCancerDNAMapper(10904): 3.016 : Xamarin.Forms.Forms.Init
I/GeneticCancerDNAMapper(10904): 3.166 : Realms.Realm.GetInstanceAsync ~Get Instance & Data~
I/GeneticCancerDNAMapper(10904): 3.571 : Realms.Realm.GetInstanceAsync ~Obtained Instance & Data~
I/GeneticCancerDNAMapper(10904): 3.571 : Xamarin.Forms.Application Content
I/GeneticCancerDNAMapper(10904): 3.772 : Xamarin.Forms.Application Content ~Creation Completed~
I/GeneticCancerDNAMapper(10904): 3.799 : Xamarin.Forms.Application.MainPage ~Displayed~
I/GeneticCancerDNAMapper(10904): 4.457 : Xamarin.Forms.Platform.Android.FormsAppCompatActivity.LoadApplication