ConstraintLayout实现左中右布局

布局如下：

<android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="56dp">

        <FrameLayout
            android:id="@+id/fl_left"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:background="@color/colorPrimary"
            app:layout_constraintHorizontal_weight="0.8"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toStartOf="@id/fl_center"/>
        <FrameLayout
            android:id="@+id/fl_center"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            app:layout_constraintHorizontal_weight="2.4"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toEndOf="@id/fl_left"
            app:layout_constraintEnd_toStartOf="@id/fl_right"
            />
        <FrameLayout
            android:id="@+id/fl_right"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            app:layout_constraintHorizontal_weight="0.8"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toEndOf="@id/fl_center"
            app:layout_constraintEnd_toEndOf="parent"
            />

    </android.support.constraint.ConstraintLayout>