MotionLayout技术问询：仅配置动画变更属性与多状态过渡简化方案

1. Can I only include changed attributes in ConstraintSets? #

Absolutely! You don’t need to duplicate all constraint properties across every ConstraintSet in your MotionScene. MotionLayout automatically inherits unchanged attributes from the base ConstraintSet (usually the one marked as the initial state, e.g., app:initialConstraintSetId="@+id/state_default").

Here’s how it works:

• Define all your static, unchanging layout properties (like layout_width, layout_height, or fixed constraints) in your base ConstraintSet.
• For other ConstraintSets that represent animated states, only include the attributes that actually change during the animation (e.g., layout_constraintStart_toStartOf, alpha, scaleX).

For example:

<ConstraintSet android:id="@+id/state_default">
    <Constraint android:id="@+id/animated_view">
        <Layout
            android:layout_width="100dp"
            android:layout_height="100dp"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"/>
    </Constraint>
</ConstraintSet>

<ConstraintSet android:id="@+id/state_moved">
    <Constraint android:id="@+id/animated_view">
        <!-- Only the changed constraint is included -->
        <Layout app:layout_constraintEnd_toEndOf="parent"/>
    </Constraint>
</ConstraintSet>

In this case, layout_width, layout_height, and the top constraint from state_default are automatically applied to state_moved—no need to repeat them. This keeps your MotionScene clean and avoids redundancy.

2. Can I use fewer transitions to switch between any states? #

Yes, you don’t need to define 6 bidirectional transitions for 3 states. Instead, you can create 3 unidirectional transitions that target each specific state, regardless of the current state. MotionLayout will handle animating from the current active state to the target state automatically.

Here’s how to set this up in XML:

1. Define your 3 ConstraintSets (e.g., state_a, state_b, state_c).
2. Create 3 transitions, each mapping from any current state to one of your target states. You don’t need to specify a constraintSetStart for these transitions—MotionLayout uses the current state as the starting point.
3. Link each button to trigger the corresponding transition using OnClick in your MotionScene.

Example MotionScene snippet:

<!-- ConstraintSets for your 3 states -->
<ConstraintSet android:id="@+id/state_a">...</ConstraintSet>
<ConstraintSet android:id="@+id/state_b">...</ConstraintSet>
<ConstraintSet android:id="@+id/state_c">...</ConstraintSet>

<!-- Transitions to each target state -->
<Transition
    android:id="@+id/to_state_a"
    app:constraintSetEnd="@+id/state_a"
    app:duration="300">
    <OnClick
        app:targetId="@+id/btn_go_to_a"
        app:transitionId="@+id/to_state_a"/>
</Transition>

<Transition
    android:id="@+id/to_state_b"
    app:constraintSetEnd="@+id/state_b"
    app:duration="300">
    <OnClick
        app:targetId="@+id/btn_go_to_b"
        app:transitionId="@+id/to_state_b"/>
</Transition>

<Transition
    android:id="@+id/to_state_c"
    app:constraintSetEnd="@+id/state_c"
    app:duration="300">
    <OnClick
        app:targetId="@+id/btn_go_to_c"
        app:transitionId="@+id/to_state_c"/>
</Transition>

When you click btn_go_to_a, MotionLayout will animate from whatever state the layout is currently in (A, B, or C) directly to state_a—no need for separate transitions from B→A or C→A. This cuts your transition count from 6 to 3, exactly what you’re looking for.

One thing to note: If you want custom easing or interpolators for specific state transitions, you can still define those separately, but for basic state switching, this 3-transition approach works perfectly.

内容的提问来源于stack exchange，提问作者Vladimir Ilyin