Transparent background on CardView - Android

In my case, I used the attribute android:backgroundTint="@color/some_color",it is only used en API level 21 and higher. And color #50000000 for example.

<android.support.v7.widget.CardView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        card_view:cardCornerRadius="3dp"
        app:cardElevation="0dp"
        android:backgroundTint="@color/negro_label"
        >

in SDK version 21 or higher steps to make Android CardView transparent.

1. Set android:backgroundTint="@android:color/transparent". This is CardView attribute to set background.

2. Set android:cardElevation="0dp" to remove the shadow.

For example, here is small xml code to create transparent CardView

<androidx.cardview.widget.CardView
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/card_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:cardBackgroundColor="@android:color/transparent"
        app:cardElevation="0dp" />

Setup your CardView to use the cardBackgroundColor attribute to remove color and cardElevation attribute to remove the drop shadow. For example:

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/myCardView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    card_view:cardBackgroundColor="@android:color/transparent"
    card_view:cardElevation="0dp"> 

For a full list of supported attributes see here: https://developer.android.com/reference/android/support/v7/widget/CardView.html

If you are using an older API, you will need to call these two functions on your CardView instead:

myCardView.setCardBackgroundColor(Color.TRANSPARENT);
myCardView.setCardElevation(0);