Enhancing Shared Element Transitions: Expanding Views Seamlessly

Smooth Transitions in Android: Expanding Views with Style

Have you ever noticed how some apps transition smoothly between screens, making elements appear to grow naturally from one state to another? This effect, known as the SharedElementTransition API in Android, enhances user experience by creating fluid animations between activities. However, achieving the perfect expansion effect can be tricky, especially when transitioning between views of different sizes. 📱

By default, the ChangeBounds transition might not behave as expected, causing the new view to start zoomed in and then shrink outward. This is a common challenge for developers trying to create a seamless scaling effect. Instead of achieving a true expansion, the transition can feel abrupt and unnatural, breaking immersion for users. 😕

Imagine you’re designing a gallery app where a user taps on a thumbnail to open an image in full screen. You’d want the image to expand outward smoothly rather than suddenly appear enlarged. The default transitions might not provide the ideal effect, but there are ways to fine-tune them to achieve the desired outcome.

In this guide, we'll explore how to manipulate the SharedElementTransition API to create a seamless expanding animation. You'll learn how to modify transitions, apply scale effects, and ensure a natural flow between activities for an engaging user experience.

Mastering Shared Element Transitions for Seamless UI

In the previous examples, we explored how to use the SharedElementTransition API to create smooth animations between activities in Android. The first script utilized the makeSceneTransitionAnimation() method, which allows an element to transition seamlessly from one screen to another. This method helps preserve visual continuity, making the UI feel more responsive and dynamic. However, since the default behavior may not always produce the desired effect, we implemented a custom SharedElementCallback to properly map the shared elements and ensure the second view expands correctly.

To further refine the transition, we introduced ObjectAnimator in the second script. This allowed us to manually control the scale and transparency of the shared element during the transition. By combining scaleX, scaleY, and alpha animations using AnimatorSet.playTogether(), we created a more natural effect where the element smoothly expands outward rather than appearing abruptly. Imagine an image gallery where a user taps on a thumbnail, and instead of just appearing larger, the image fluidly grows to take up the whole screen. This kind of effect enhances user engagement and makes the interface feel polished. 📱

Testing is a crucial part of implementing animations, as unexpected issues can arise depending on device performance and UI complexity. That’s why we included a unit test using Espresso in the third script. This test ensures that after clicking on the shared element, the full-screen version is properly displayed. The test uses withId() to find the elements and matches(isDisplayed()) to verify that the transition completes successfully. Without testing, an animation may work perfectly on one device but behave inconsistently on another, leading to a broken user experience.

By combining these approaches—custom callbacks, manual animations, and proper testing—we ensure a smooth, optimized transition between activities. Whether you're developing a media viewer, an e-commerce app with product zoom-ins, or a social platform with profile image expansions, these techniques can be adapted to suit various needs. The key takeaway is that Android’s default transitions are powerful but often require fine-tuning to achieve the best results. With the right adjustments, you can create visually stunning and highly engaging interfaces that users will love. 🚀

// Solution 1: Custom SharedElementCallback for Smooth Scaling
class FullScreenTransitionCallback : SharedElementCallback() {
    override fun onMapSharedElements(names: List<String>, sharedElements: MutableMap<String, View>) {
        sharedElements[names[0]] = findViewById(R.id.fullScreenView)
    }
}

val options = ActivityOptionsCompat.makeSceneTransitionAnimation(
    this, sharedElementView, sharedElementName
)

val intent = Intent(this, FullScreenActivity::class.java)
startActivity(intent, options.toBundle())

// Solution 2: Custom ObjectAnimator to Scale View Smoothly
val scaleX = ObjectAnimator.ofFloat(sharedElementView, "scaleX", 1f, 1.5f)
val scaleY = ObjectAnimator.ofFloat(sharedElementView, "scaleY", 1f, 1.5f)
val alpha = ObjectAnimator.ofFloat(sharedElementView, "alpha", 0f, 1f)

val animatorSet = AnimatorSet()
animatorSet.playTogether(scaleX, scaleY, alpha)
animatorSet.duration = 300
animatorSet.start()

@RunWith(AndroidJUnit4::class)
class SharedElementTransitionTest {

    @get:Rule
    val activityRule = ActivityScenarioRule(MainActivity::class.java)

    @Test
    fun testSharedElementTransition() {
        onView(withId(R.id.sharedElementView)).perform(click())
        onView(withId(R.id.fullScreenView)).check(matches(isDisplayed()))
    }
}

Advanced Techniques for Shared Element Transitions

One key aspect of refining the SharedElementTransition experience is handling window transitions. By default, Android applies system-defined animations when an activity starts or finishes, which can sometimes interfere with the shared element animation. To counter this, we can use getWindow().setSharedElementEnterTransition() and getWindow().setSharedElementReturnTransition() to define custom transitions that complement the element’s scaling behavior.

Another crucial factor is managing different screen sizes and orientations. If a user rotates their device mid-transition, the animation might break or reset unexpectedly. A best practice here is to save and restore transition states using ActivityReenterCallback. This ensures that when a user navigates back, the shared element smoothly returns to its original position instead of jumping abruptly.

Finally, performance optimization is essential, especially for complex UI transitions. Using ViewCompat.setTransitionName() allows developers to dynamically assign transition names at runtime, making animations more flexible. Additionally, reducing overdraw by using a FrameLayout as a placeholder during transitions can prevent visual glitches. For instance, in a video player app, a paused video thumbnail can transition into a full-screen player, creating a seamless effect instead of an abrupt change. 🎥