扩展 MaterialCardView 不应用主题

Question

According to the material specifications https://material.io/develop/android/components/material-card-view/ colorSurface applies to the card's Background color .

This works when we are specifying the card in our xml like this

<com.google.android.material.card.MaterialCardView
    android:layout_width="100dp"
    android:layout_height="100dp"></com.google.android.material.card.MaterialCardView>

When I run this I can see color surface properly being applied to the above card.

This also works if I make a card programmatically

addView(MaterialCardView(this).apply {
        layoutParams = ViewGroup.LayoutParams(300,300)
    })

However once I extend from MaterialCardView to make my own custom view , it appears as if the theme connection to this is lost . The color surface is not applied rather the card defaults to white

class CustomView @JvmOverloads constructor(
    context: Context?,
    attributeSet: AttributeSet? = null,
    defStyleAttr: Int = 0
) : MaterialCardView(context, attributeSet, defStyleAttr){

}


<com.seed.formviewactivity.CustomView
        android:layout_width="100dp"
        android:layout_height="100dp"></com.seed.formviewactivity.CustomView>

My CustomView now doesn't have the colorSurface applied.

Is this a known issue ?

Answer 1

In your constructor you are using defStyleAttr: Int = 0 .
You should apply the R.attr.materialCardViewStyle as default value instead of 0 .

In this way your custom CardView will use the style defined in you app theme by materialCardViewStyle attribute.

The default value provided by the Material Components Library is:

<style name="AppTheme" parent="Theme.MaterialComponents.DayNight">
  <!-- ... -->
  <item name="materialCardViewStyle">@style/Widget.MaterialComponents.CardView</item>
</style>