ConstraintLayout 2.0.0 alpha 3

We just released ConstraintLayout 2.0.0 alpha 3. It’s available from the google maven repository:

dependencies {

implementation 'com.android.support.constraint:constraint-layout:2.0.0-alpha3'

}

or if using the AndroidX packages:

dependencies {

    implementation 'androidx.constraintlayout:constraintlayout:2.0.0-alpha3'

}

Changes

This release contains various bug fixes and performance improvements:

• Barrier fixes
• Chains optimizations
• Fixed glitches in MotionLayout touch handling (end state could be triggered incorrectly)

We also added several new features to MotionLayout:

• New XML format for specifying ConstraintSets, allowing finer-grained overrides
• KeyTimeCycle : a keyframe that allows you to define a cycle driven by time instead of by the transition (e.g. a pulsating color defined this way will keep pulsating even if the overall transition is stopped)
• KeyPosition now supports percentWidth/percentHeight
• KeyTrigger : a keyframe that can fire callbacks depending on the current animation progress
• Supports custom interpolators (referencing a Framework XML interpolator)
• Touch interactions can now drive multiple state transitions seamlessly one after another
• OnClick: now supports multiple OnClick per MotionScene. Important: motion:mode has been renamed to motion:clickAction.
• Added ImageFilterButton, an equivalent of ImageFilterView but extending ImageButton
• Added new callbacks in TransitionListener

New XML Format for ConstraintSet

An important addition in alpha 3 is a new way of defining ConstraintSet in the MotionScene file. Previously, <Constraint> elements had to contain all attributes defined on a view (as we replace everything when you apply them). Now, you can instead only add the specific areas you are modifying, as sub-elements of <Constraint>:

• <Layout> : layout-related (constraints) attributes
• <PropertySet> : visibility, alpha and progress
• <Transform> : scale, translation, rotation, pivot, elevation
• <Motion> : easing, arc motion, etc.

For example, let's say that you wanted to only modify the rotation of a widget in a ConstraintSet. Previously you would have needed to repeat all the attributes to preserve the position of the widget:

         <Constraint

            android:id="@+id/button"

            android:layout_width="64dp"

            android:layout_height="64dp"

            android:layout_marginTop="100dp"

            motion:layout_constraintStart_toStartOf="parent"

            motion:layout_constraintEnd_toEndOf="parent"

            motion:layout_constraintTop_toTopOf="parent"

            android:rotation="45" />

With alpha 3 you can instead only specify the Transform area, the rest will be unaffected:

         <Constraint  android:id="@+id/button">

            <Transform motion:rotation="45" />

         </Constraint>