[Bug] Color.Defult.MultiplyAlpha(0.30).ToAndroid() is crashing the app

[luismts]

Description

Color.Defult.MultiplyAlpha(0.30).ToAndroid() is crashing the app.

Steps to Reproduce

1. Go to the MainActivity in your Xamarin.Forms Android project.
2. Go to OnCreate(Bundle savedInstanceState) method.
3. Add the following code:

var color = Xamarin.Forms.Color.Default;
color.MultiplyAlpha(0.30).ToAndroid();

Expected Behavior

Add a default color modifying the alpha.

Actual Behavior

The app is crashing.

Basic Information

• Version with issue: 5.0.0.2012
• Platform Target Frameworks:
  • Android: Android 9 - API 28

Build Logs

Default color is:
R=-1, G=-1, B=-1, A=-1, Hue=-1, Saturation=-1, Luminosity=-1

[rachelkang]

Hi, @luismts - thanks for submitting this issue. I'm confirming that I'm able to repro it
Issue14173.zip

The app crashes with this exception

System.InvalidOperationException: Invalid on Color.Default
  at Xamarin.Forms.Color.MultiplyAlpha (System.Double alpha) [0x00019] in D:\a\1\s\Xamarin.Forms.Core\Color.cs:151
  at Issue14173.Droid.MainActivity.OnCreate (Android.OS.Bundle savedInstanceState) [0x0000f] in /Users/rachelkang/Projects/Issue14173/Issue14173.Android/MainActivity.cs:19
  at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_ (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_savedInstanceState) [0x00010] in /Users/builder/azdo/_work/278/s/xamarin-android/src/Mono.Android/obj/Release/monoandroid10/android-30/mcw/Android.App.Activity.cs:2700
  at at (wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.7(intptr,intptr,intptr)

[rachelkang]

On second thought, after chatting with @mattleibow - something to keep in mind here is that Xamarin.Forms.Color.Default is not an actual color, but just a placeholder. It's determined by the control that consumes it

[mattleibow]

One example of this is that a Button has a "Default" color for text, background, border and everything else. There is also a IsDefault property that you can use to quickly test to make sure that if it is a Default color, then you can swap out for whatever you want it to really be.

[luismts]

So, the expected behavior is correct? And the implementation is what we need to care about it?

I'm reporting this because XF-Material-Library and its latest version are experimenting some issues with this code. I also report the issue in their repo; you can see it here.

[Redth]

Yes I believe this is expected. In MAUI we are looking at nullable Color so that the 'default' is instead null and not a 'placeholder'

[luismts]

Ok, I'm closing this issue.

Thanks @Redth