Introduction to ConstraintSet

Tan Jun Rong avatar

Tan Jun Rong

Constraint Layout

ConstraintLayout has been around for a while now. There are a couple of ways to define constraints for ConstraintLayout:

So far I've been only using xml, but sometimes it is needed to define the constraints dynamically. In this post, I want to discuss how to define constraints for ConstraintLayout using ConstraintSet 👇


Let's start out with a spec. Pretend that we want to build this, placing a red row under a page:

Row at the Bottom
Row at the Bottom

Using xml

To achieve this with ConstraintLayout using xml,

The xml version looks like this:


< ... android:layout_width="match_parent" android:layout_height="match_parent"> <TextView ... android:layout_width="0dp" android:layout_height="wrap_content" android:text="Hello World" android:textSize="20dp" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" />>

The interesting part that makes the TextView sticks to the bottom of the screen and becomes as wide as the width of the screen is this 3 lines:

        app:layout_constraintStart_toStartOf="parent" />

They align the row's edges to the parents's.

Re-writing using ConstraintSet

Let's implement the same thing using ConstraintSet.

We will begin with an empty layout like below, let's called it empty_main.xml.


<ConstraintLayout android:id="@+id/constraintLayout" android:layout_width="match_parent" android:layout_height="match_parent"> ConstraintLayout>

The TextView will be in a separte file called text_view_row.xml:


xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="" android:id="@+id/textViewRow" android:layout_width="0dp" android:layout_height="wrap_content" android:background="@color/md_red_300" android:padding="30dp" android:text="Hello World" android:textColor="@color/md_white_1000" android:textSize="20dp" />

Now that we have 1 empty container constraintLayout, and a TextView in another file, we can use ConstraintSet to hook them up and reproduce the same result.

This is the code to use ConstraintSet:

fun onCreate() {    

    // 1. Inflate the TextView row & add the the TextView
    val textViewRow = LayoutInflater.from(this).inflate(R.layout.text_view_row, constraintLayout, false)
    // 2. Clone the constraints into ConstraintSet
    val set = ConstraintSet()
    // 3. Connect TextView row with ConstraintLayout
    set.connect(, ConstraintSet.BOTTOM, ConstraintSet.PARENT_ID, ConstraintSet.BOTTOM)
    set.connect(, ConstraintSet.START, ConstraintSet.PARENT_ID, ConstraintSet.START)
    set.connect(, ConstraintSet.END, ConstraintSet.PARENT_ID, ConstraintSet.END)
    // 4. applying the constraint

Following the code, I can roughly divide them into 4 steps, I will add some explanations to each steps:

  1. Inflate the TextView row

    • (self-explanatory)
  2. Clone the constraints into ConstraintSet

    • if we create a new ConstraintSet, it will be empty, so we need to clone the constraints from the constraintLayout object
  3. Connect TextView row with ConstraintLayout

    • now we have a copy of ConstraintSet of constraintLayout, we can connect it with textViewRow
    • set.connect(, ConstraintSet.BOTTOM, ConstraintSet.PARENT_ID, ConstraintSet.BOTTOM) is similar to be using app:layout_constraintBottom_toBottomOf="parent" in xml
  4. Applying the Constraint

    • finally, we apply the ConstraintSet to constraintLayout.

After this, we will get this again.

Row at the Bottom with ConstraintSet
Row at the Bottom with ConstraintSet

This is a short post and that's it!

The code is available in this Github Repo, ConstraintSetStudy.

Tan Jun Rong avatar
Written By

Tan Jun Rong

Android Programmer who likes writing blogs, reading, coffee, snowboarding.
Published in Android
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