Androidx下设置按钮背景(button backgroung)无效解决方案
解决办法：找到AndroidManifest.xml，修改application下的主题如下：
<style name="Theme.Demo" parent="Theme.MaterialComponents.DayNight.NoActionBar.Bridge">
<!-- Primary brand color. -->
<item name="colorPrimary">@color/purple_500</item>
<item name="colorPrimaryVariant">@color/purple_700</item>
<item name="colorOnPrimary">@color/white</item>
<!-- Secondary brand color. -->
<item name="colorSecondary">@color/teal_200</item>
<item name="colorSecondaryVariant">@color/teal_700</item>
<item name="colorOnSecondary">@color/black</item>
<item name="android:textColorSecondary">@android:color/white</item>
<!-- Status bar color. -->
<item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
<!-- Customize your theme here. -->
</style>
关键：当前主题下添加.Bridge即可
