LinearLayout flagged if used in CardView

问题

I have used a LinearLayout in a CardView to get a kind of social media login button look and it all runs fine, but Android Studio flags Element LinearLayout is not allowed here. I was wondering why this may be the case? My xml is this :

<android.support.v7.widget.CardView
            xmlns:card_view="http://schemas.android.com/apk/res-auto"
            android:layout_below="@id/cv_fb"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            card_view:cardElevation="3dp"
            >

            <LinearLayout

                android:id="@+id/ll_entitlement_extend_google"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal"
                android:background="@color/white"
                android:clickable="true"
                android:gravity="center"
                android:paddingTop="10dp"
                android:paddingBottom="10dp"
                >

                <ImageView
                    android:layout_weight="1"
                    android:layout_width="75dp"
                    android:layout_height="75dp"
                    android:src="@drawable/google_icon"/>

                <TextView
                    android:layout_weight="1"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="Connect with Google +"/>

                <ImageView
                    android:layout_weight="1"
                    android:layout_width="25dp"
                    android:layout_height="25dp"
                    android:src="@drawable/ic_chevron_right_black"/>


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

回答1:

Just to have a proper answer, as @Blacklight said in comments, it is an IDE issue so restarting it should fix the problem.

回答2:

Apart from other suggestions and the above answer, this issue happenes on me if I didn't upgrade my support library to AndroidX, in this case is CardView. So from