ConstraintLayout Tools
Question
ConstraintLayout- guidelines vs barriers, groups
Short interview answer
A guideline is a fixed or proportional invisible reference line; a barrier positions itself from the edge of referenced views; a group controls the visibility of several views together. They describe different kinds of layout relationships.
Detailed answer
Use a guideline when several elements share a design alignment, a barrier when a control must begin after whichever referenced label is widest, and a group for views that appear or disappear together:
<androidx.constraintlayout.widget.Guideline
android:id="@+id/contentGuideline"
app:layout_constraintGuide_percent="0.32" />
<androidx.constraintlayout.widget.Barrier
android:id="@+id/labelEnd"
app:barrierDirection="end"
app:constraint_referenced_ids="title,subtitle" />
These helpers keep the relationship declarative instead of calculating positions in code.