Android Cardview elements stack on top of each other

You can use LinearLayout instead of RelativeLayout for that

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/currentData"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    card_view:cardCornerRadius="4dp"
    card_view:cardBackgroundColor="@color/orange">

    <LinearLayout
        android:id="@+id/cardviewLayout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:padding="10dp"
        android:weightSum="2"
        android:orientation="vertical">

        <TextView
            android:id="@+id/time"
            tools:text="this is the time"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_above="@+id/temperature"
            android:weight="1"
            android:textColor="@color/white"/>

        <TextView
            android:id="@+id/temperature"
            tools:text="50°"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:weight="1"
            android:textSize="50sp" />

    </LinearLayout>

</android.support.v7.widget.CardView>

or if you want to use RelativeLayout you can use this trick

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/currentData"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    card_view:cardCornerRadius="4dp"
    card_view:cardBackgroundColor="@color/orange">

    <RelativeLayout
        android:id="@+id/cardviewLayout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:padding="10dp"
        android:orientation="vertical">

        <View
            android:id="@+id/anchor_view"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:layout_centerInParent="true"/>

        <TextView
            android:id="@+id/time"
            tools:text="this is the time"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_centerHorizontal="true"
            android:layout_centerVertical="true"
            android:layout_above="@+id/anchor_view"
            android:textColor="@color/white"/>

        <TextView
            android:id="@+id/temperature"
            tools:text="50°"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_centerHorizontal="true"
            android:layout_centerVertical="true"
            android:layout_below="@+id/anchor_view"
            android:textSize="50sp" />

    </RelativeLayout>

</android.support.v7.widget.CardView>

This way the anchorview will be located in the middle of the parent view but won't be drawed because the width and the height is zero but it will be come the reference for time and temperature so time will fill the upper half and temperature will fill the bottom half