When an app is letterboxed, stretched, clipped by the hinge, caught in a rotation loop, or showing a sideways camera preview on a foldable, the cause is usually that the app is treating a changing app window like a fixed phone display. Check the activity’s resizability and orientation restrictions, then drive layouts from the current window metrics, account for the fold as an occlusion boundary, preserve state across recreation, and test every posture and window mode.
Why foldables expose problems that phones hide
A foldable can present several different app windows without changing the app package: a narrow cover screen when closed, a wide inner display when open, a half-open tabletop or book posture, split-screen, picture-in-picture, or a freeform desktop-style window. Each state can change the available width, height, aspect ratio, orientation and the portion of the display allocated to the app.
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The physical screen is not the same thing as the app window. A split-screen pane or desktop window may occupy only part of the display, so a layout based on the device’s total dimensions can choose the wrong number of columns, make controls too wide, or place content outside the visible area. The reliable input is the current app-window geometry reported through Jetpack WindowManager and Android window metrics.
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What letterboxing and a restart button mean
Android can place an activity in size compatibility mode when it is non-resizable or constrained by orientation or aspect-ratio declarations. The system preserves the activity’s expected shape by adding letterboxing, which explains black or empty bands around a phone-shaped interface on the inner display. Some devices also show a control to restart the app in a different compatibility configuration.
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A non-resizable activity can fail in multi-window rather than merely looking small. A fold or unfold can also stop and recreate the activity. If the app does not save its form fields, navigation position and other state, the user may see an apparent reset even when the underlying layout is correct.
What changed with Android 16
For apps targeting Android 16 (API level 36), Android treats activities as resizable on displays whose smallest width is at least 600dp. That includes the inner displays of many large-screen foldables, and those activities can enter multi-window. Displays below 600dp are exceptions; many cover screens and some flippable phones fall into this category, so an app must still behave correctly on the smaller screen.
Google Play is scheduled to require API level 36 targeting in August 2026. Raising the target does not automatically repair a layout, camera preview or state-management bug; it does make previously hidden assumptions visible on more large-screen configurations.
Start with a reproducible symptom report
Before changing code, record exactly when the failure occurs. Use the same account and data while repeating the test so that a state-loss bug is not mistaken for a layout bug.
- Test each physical state: closed cover screen, fully open inner screen, half-open tabletop, and half-open book posture when the device supports them.
- Test each window state: portrait, landscape, split-screen, picture-in-picture entry and exit, freeform or desktop-style windows, attachment windows, and multiple app instances.
- Record the visible failure: letterboxing, stretched controls, clipped content, a control hidden behind the hinge, rotation or restart looping, lost form input, or a camera preview that is cropped, stretched or sideways.
- Capture the transition: note whether the problem appears during folding, unfolding, rotation, resizing, entering split-screen or returning from picture-in-picture.
- Save device context: Android version, target SDK, screen used (cover or inner), posture and whether another app was sharing the display.
This matrix distinguishes a manifest compatibility problem from a layout decision, lifecycle error or camera-specific transform.
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Remove manifest restrictions that force a phone-shaped window
Inspect both the application element and every affected activity. The most common restrictions are android:resizeableActivity, a fixed android:screenOrientation, and narrow android:minAspectRatio or android:maxAspectRatio values.
Make activities resizable
For older Android behavior, set the activity or application to resizable unless there is a demonstrable platform requirement preventing it:
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<application android:resizeableActivity="true" ...>Remove a duplicate activity-level declaration that overrides the application setting. Verify the built manifest, not only the source manifest, because product flavors or library manifests can reintroduce a restriction.
Reconsider fixed orientation
A declaration such as portrait-only can prevent the app from adapting when the available window becomes landscape after unfolding or entering a wide split-screen pane. Remove it when the interface can support both orientations. If a particular activity truly needs one orientation, isolate that decision and provide a deliberate fallback for the other window states rather than applying a global lock.
Review aspect-ratio limits
Minimum and maximum aspect-ratio declarations can trigger compatibility mode on a tall cover display or a wide inner display. Delete values that were added only to protect an old phone layout. If a limit is unavoidable, test the resulting letterboxed experience and make sure important controls remain reachable inside the compatible region.
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Stop rotation loops and repeated restarts
Do not call Activity#setRequestedOrientation() from onCreate() merely to establish a default portrait or landscape state. On a foldable, the window can legitimately change while the activity is being created or resumed; repeatedly requesting a different orientation can cause flicker, recreation and an apparent endless restart.
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- Base layout decisions on the current window bounds and window size class.
- Allow the system to manage ordinary configuration changes unless the activity has a specific, tested reason to handle them itself.
- When an orientation request is unavoidable, make it conditional on the actual product requirement and ensure the request cannot alternate on every recreation.
- Log the window size, requested orientation and lifecycle transitions during testing; a repeating sequence of create, resume and orientation requests identifies the loop quickly.
Drive the interface from current window metrics
Jetpack WindowManager provides the app’s current WindowMetrics. Use those bounds and window size classes whenever the window changes, including split-screen and freeform modes. Do not use the physical device dimensions as a proxy for the area your activity can draw in.
Use meaningful layout thresholds
Choose breakpoints based on what the interface needs, not on a particular foldable model. At a narrow width, keep a single navigation destination visible and make secondary actions reachable by scrolling. At a wider width, a list and detail pane or a persistent navigation rail may fit. When the window crosses a threshold, reflow or replace components instead of scaling every phone control proportionally.
A responsive single layout is appropriate when the same hierarchy can reflow cleanly. A size- or posture-specific layout is better when the number of panes, navigation model or location of primary actions must change materially. Both approaches should consume the same state and data so a transition does not discard the user’s context.
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Prevent stretched and clipped controls
- Give text fields, dialogs and reading surfaces a maximum width so they do not become difficult to scan across the entire inner screen.
- Use flexible constraints for buttons and rows, but set minimum touch targets and allow labels to wrap or scroll.
- Make long forms and landscape views vertically scrollable; a short window can push the submit button below the fold even when the layout appears correct at full height.
- Check system-bar insets and cutouts after every posture change so content is not hidden beneath a bar or outside the app’s visible bounds.
Keep content away from the fold and hinge
In a half-open tabletop or book posture, the crease or hinge is an occlusion boundary, not ordinary empty space. Text crossing it can be unreadable, and a button centered on the fold may be impossible to press. Read the fold and hinge features exposed by WindowManager and reserve the occluded rectangle when laying out content.
Choose a placement strategy
- Single-pane content: move the primary content entirely to the unobstructed side and retain a clear scrolling path.
- Two-pane content: split a list and detail view into the available left/right or top/bottom regions when the posture and window size make that separation useful.
- Dialogs and menus: anchor them to the active pane rather than centering across the full physical display.
- Primary actions: keep confirmation, navigation and playback controls in a region that remains visible and touchable in both folded and half-open states.
Re-test text selection, drag gestures and accessibility focus order. A visual gap that avoids the hinge is not sufficient if keyboard or screen-reader focus still lands on an occluded element.
Preserve continuity when the activity is recreated
Folding, unfolding, rotation and window resizing can stop and restart an activity. Save transient input, selected tabs, navigation position, expanded sections and any in-progress operation that the user expects to survive. Restore that state after recreation before rendering the final layout.
- Identify state that exists only in views or a temporary controller and list what a user would consider “not finished yet.”
- Store small, restorable values through the activity’s saved-state mechanism and keep longer-lived data in the app’s normal persistent storage.
- Restore the navigation destination and form values before requesting focus or scrolling, otherwise the restored content may jump to the wrong position.
- Test an unfold and refold while editing, while a dialog is open and while the app is in split-screen. Confirm that unsent text, selections and pending actions remain available.
Do not hide lifecycle failures by disabling recreation. That can leave stale dimensions, leak resources and still fail when the process is reclaimed.
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Treat camera previews as a separate problem
A camera can be correctly opened while its preview is wrong. Test preview rotation, crop, stretch and sensor-to-UI aspect-ratio handling independently on the cover and inner screens, in portrait and landscape, folded and unfolded.
- Verify that the preview surface follows the current app window rather than the physical sensor’s fixed orientation.
- Compare the preview framing with captured output; a cropped preview can make users aim incorrectly even when the saved image is full frame.
- Check front and rear cameras separately where both are available, including the transition that keeps the camera open while the device changes posture.
- Repeat after entering split-screen or a desktop-style window, because the preview may be resized without a sensor rotation.
Keep camera initialization and transformation calculations resilient to recreation. A preview that briefly appears sideways after every fold usually indicates that the surface transform is being applied before the new window metrics are known or is being applied twice.
Build a foldable test matrix before shipping
Use Pixel Fold and tablet emulators or equivalent large-screen profiles to exercise the app without waiting for physical hardware. Android’s compatibility framework also provides the UNIVERSAL_RESIZABLE_BY_DEFAULT flag, which helps expose assumptions that Android 16 will make invalid on large displays.
Minimum scenarios
- Closed cover screen to fully open inner screen, and the reverse transition.
- Half-open tabletop and book postures, with dialogs, menus and primary actions visible.
- Portrait-to-landscape rotation in each screen state.
- Manual split-screen resizing from narrow to wide and back again.
- Picture-in-picture entry and exit, including returning to the previous navigation position.
- Attachment windows, multiple app instances and any desktop-window mode supported by the device.
- Camera preview on every supported camera and screen combination.
- Accessibility traversal and keyboard focus after every resize and posture change.
For each scenario, record whether the app remains interactive, whether state survives, whether any control is occluded, and whether the system places the activity in compatibility mode. A passing screenshot is not enough; continuity and input reachability are part of the result.
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| Approach | Best fit | Strength | Risk to check |
|---|---|---|---|
| Responsive single layout | The same hierarchy can reflow across widths | One navigation structure and fewer divergent screens to maintain | Phone controls may stretch or become cramped unless width limits and scrolling are explicit |
| Size-specific adaptive layout | Navigation, pane count or content density changes at width thresholds | Each window range gets an intentional arrangement | State can be lost or duplicated if transitions are treated as separate screens |
| Posture-specific placement | The hinge or fold changes where content can be safely shown | Dialogs, controls and reading surfaces avoid occlusion in tabletop or book mode | More combinations to test, especially when posture and split-screen occur together |
Whichever approach you choose, compare it against six outcomes: adaptation to current window size; folded, unfolded, tabletop and book behavior; continuity after recreation; multi-window and picture-in-picture; camera correctness; and control accessibility near the hinge.
Symptom-to-fix checklist
| Symptom | Most likely cause | First check |
|---|---|---|
| Letterboxed inner display or a restart control | Non-resizable activity or restrictive aspect ratio/orientation | Inspect the merged manifest and remove unnecessary restrictions |
| Controls stretched across the open screen | Layout uses fixed phone assumptions or device dimensions | Use current WindowMetrics and apply maximum content widths |
| Buttons or text hidden by the hinge | No fold-feature or occlusion handling | Reserve the hinge region and place content in separate available areas |
| App rotates, flickers or restarts repeatedly | Orientation requested during creation or inferred from physical rotation | Remove unconditional setRequestedOrientation() calls and log transitions |
| Form fields clear after unfolding | Activity recreation without state restoration | Save and restore input, navigation and scroll state |
| Camera preview is sideways, cropped or stretched | Sensor, surface and window aspect-ratio transforms disagree | Test each camera and posture with a newly measured app window |
| Works full-screen but fails in split-screen | Code uses physical display size or assumes unlimited width/height | Resize manually and recalculate from app-window metrics |
Release checklist
- The merged manifest permits resizing where the activity supports it.
- Fixed orientation and aspect-ratio declarations have a documented reason and a tested fallback.
- No lifecycle path repeatedly requests orientation during creation or resume.
- Layouts respond to current app-window metrics, not hard-coded device dimensions.
- Long content scrolls and wide content has deliberate maximum widths.
- Fold and hinge occlusion is handled for dialogs, menus, text and primary controls.
- Input, navigation, selection and scroll state survive recreation.
- Camera preview rotation and framing are correct on every supported screen and posture.
- Folded, unfolded, half-open, rotated, split-screen, picture-in-picture, attachment-window and multi-instance tests are recorded.
- Large-screen testing includes Android 16 behavior for API-level-36-targeting builds and sub-600dp cover-screen exceptions.
A foldable-ready app is not one that merely fills the inner display. It measures the window it actually receives, adapts its structure when that window changes, avoids the hinge, survives recreation and keeps camera transforms tied to the current geometry.
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