[dialog] ?attr/colorControlHighlight used for android:background

Description: mtrl_alert_dialog.xml and m3_alert_dialog.xml use ?attr/colorControlHighlight for android:background

?attr/colorControlHighlight is a color value while android:background expects a drawable. Using simple color values for android:background works but using a color selector causes a crash because it’s being interpreted as a drawable.

This makes it impossible to set color ripples to anything else than primitive color values. A common thing is to use a color selector to apply an alpha to another color attribute as explained e.g. here: https://material.io/blog/android-material-theme-color (section “Color with alpha”).

So basically following the guidelines from the Material Design blog with Material Components for Android leads to a crash when showing dialogs 👍

Expected behavior: No crash

Source code:

1. Create a color selector, e.g.

<!-- In res/color/primary_60.xml -->
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:alpha="0.6" android:color="?attr/colorPrimary" />
</selector>

1. In your app theme set colorControlHighlight:

<item name="colorControlHighlight">@color/primary_60.xml</item>

1. Create and show a Material dialog:

MaterialAlertDialogBuilder(context)
    ...
    .show()

1. Crash

Android API version: 30 - possibly all 26 and 28, possibly 28 and lower. 29+ works fine.

Material Library version: master, the issue can be clearly seen in source code. Search for colorControlHighlight in mrtl_alert_dialog.xml and m3_alert_dialog.xml files in this repository.

Device: any? reproducible on an emulator.

Suggested fixes:

• define a proper color drawable that uses ?attr/colorControlHighlight and set that in android:background,
• use a different color - why would a ripple color be used for backgrounds?

[drchen]

Yeah the fix is only applied to Material 3.

It’s not a trivial fix with Material 2 and also Material 2 is basically frozen now. Please migrate to Material 3 or avoid using CSL with colorControlHighlight.

[SergeyKudryashov]

Isn’t fixed in the version 1.6.0-rc01 for MaterialComponents.