android xml中设置自适应图片

??? <ImageView android:id="@+id/image_view"?
??????? android:layout_width="wrap_content"
??????? android:layout_height="wrap_content"
??????? android:adjustViewBounds="true"
??????? android:maxWidth="42dp"
??????? android:maxHeight="42dp"
??????? android:scaleType="fitCenter"

??????? android:layout_marginLeft="3dp"

??????? android:src="@drawable/exit"
??????? />