Is it necessary to specify which element is above another element in a ConstraintLayout?-CodePudding

Imagine I have the following elements in a ConstraintLayout:

<androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <View
            android:id="@ id/view1"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:background="@color/blue" 
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"/>

        <View
            android:id="@ id/view2"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:background="@color/black"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>

As a result it is only shown the black view (view2) because it is above (graphically, not in the xml) the blue view(view1)

Now my question is, do I need to specify which element is above another element with some attribute or it is already specified by putting one element below another in the xml?

I mean I have seen that if element 1 is below element 2 in the xml file, then, element 1 is actually above element 2 although element 1 is below element 2 in the xml file and that is a little confusing...

CodePudding user response：

Let's create a function that gives us to child views of the given view, paste below code to your fragment:

    private fun View.getAllChildren(): List<View> {
        val result = ArrayList<View>()
        if (this !is ViewGroup) {
            result.add(this)
        } else {
            for (index in 0 until this.childCount) {
                val child = this.getChildAt(index)
                result.addAll(child.getAllChildren())
            }
        }
        return result
    }

Now give our ConstraintLayout an id:

    android:id="@ id/cl_parent"

And use our function on this parent to get it's children. Then loop through it and paste view names into Log You can paste below to your onViewCreated or elsewhere:
If you want to use elevations, just add something like android:elevation="1dp" to your first view and android:elevation="2dp" for your second view in xml file:

        for (childView in cl_parent.getAllChildren()) {
            val fullName = resources.getResourceName(childView.id)
            val elevationValue = childView.elevation.toString()
            Log.e("childView", "$fullName $elevationValue")
        }

This will give you view names and elevations of them. The higher value will be on top and visible to user. In your case: Output:

:id/view1 2.75
:id/view2 5.5