The hard parts of mobile app development are mostly about variety and rules: many screen shapes and sizes, stability that the stores measure, review and privacy requirements that can block a release, security you must design in, and platform requirements that change every year. Each has a known fix. Build flexible layouts, watch crash and ANR rates, meet the store guidelines before you submit, treat the app's data carefully and plan yearly maintenance.
Key takeaways
- Android's documentation says not to hardcode the position and size of UI components, and to provide different layouts for the space available on different devices; apps must also handle window changes such as multi-window mode and foldables.
- Android vitals thresholds: keep the overall user-perceived crash rate under 1.09% and the ANR (app not responding) rate under 0.47%, and under 8% on any single phone model; Google Play may reduce visibility or show a warning if you exceed them.
- Apple's App Review Guidelines reject apps that crash, show placeholder content or lack a demo account for login, and require a privacy policy, consent and in-app account deletion where accounts can be created.
- Apple says apps "should include features, content, and UI that elevate it beyond a repackaged website".
- Budget for store-required updates every year; see Mobile app technologies in 2026.
Challenge 1: so many screens and devices
Phones, tablets, foldables, resizable windows and different pixel densities mean the space your app gets is not the size of the device. Android's documentation explains that the app's screen size is not the actual screen size, because orientation, system bars and multi-window mode change it.
What to do:
- Use flexible, relative layouts instead of hardcoded sizes, so views stretch as space grows.
- Design alternative layouts for meaningfully different sizes, such as a two-pane layout on a tablet.
- Use density-independent units and vector graphics so icons look sharp at any size.
- Test on a spread of real devices, including a foldable; Android says an app that works well in multi-window mode at various sizes usually behaves well on foldables.
Challenge 2: stability the store measures
Google Play's Android vitals tracks the user-perceived crash rate and ANR rate over the last 28 days. Its thresholds:
| Metric | Overall | Per phone model |
|---|---|---|
| User-perceived crash rate | 1.09% | 8% |
| User-perceived ANR rate | 0.47% | 8% |
Google says that if you exceed a threshold, Play may reduce the visibility of your title and may show users a warning on your store listing.
What to do: add crash reporting from the first build, fix the crashes and ANRs that affect the most users first, test slow networks and low-memory devices, and release to a small percentage of users before everyone.
Challenge 3: getting through App Store review
Apple's App Review Guidelines are specific, and most rejections come from avoidable things:
- Completeness (2.1): submit final versions with no placeholder text or empty websites; include a demo account and make sure your back end is on if there is a login; crashes and obvious bugs are rejected.
- Accurate metadata (2.3): descriptions, screenshots and previews must reflect the app's core experience, and hidden or undocumented features are not allowed.
- Minimum functionality (4.2): the app must go beyond a repackaged website and work on its own.
- Privacy (5.1): link a privacy policy in App Store Connect and in the app, get consent before collecting data, request only data relevant to the core functionality, offer account deletion inside the app if users can create accounts, and ask permission through App Tracking Transparency before tracking. Apple also says you must disclose where personal data is shared with third parties, including third-party AI, and get explicit permission.
What to do: run Apple's checklist before every submission, write review notes for anything non-obvious and keep screenshots current. For Canadian and Indian privacy angles on AI features, see Privacy for AI features: Canada and India.
Challenge 4: security and data
Security has to be designed in, not added at the end. Use OWASP's Mobile Application Security Verification Standard as a checklist (storage, cryptography, authentication, network communication, platform interaction, code quality, resilience and privacy), keep secrets off the device, and ask for the minimum permissions. Our hiring guide, How to hire an app development company in 2026, shows how to check a team on this.
Challenge 5: platforms keep moving
Both stores raise their requirements every year, such as new SDK versions and target API levels, and operating systems change what apps may do in the background. Plan an update budget, keep dependencies current and test on beta operating systems before release. Choosing between native and cross-platform affects how much work this is; see Cross-platform or native in 2026.
What about AI features?
AI features add their own challenges: model limits on the device, cost and delay in the cloud, wrong answers and privacy. Decide what runs on the device and what runs on a server, add a fallback, label AI output and have a person review the content that matters.
A checklist before launch
- Layouts tested on small, large and foldable screens and in both orientations.
- Crash reporting on, and a plan for the crash and ANR thresholds.
- App Review checklist passed, with demo account and notes.
- Privacy policy linked, consent and account deletion in place.
- Security review against the standard.
- Yearly update and store-requirement budget agreed.
If you need help, see our app development page.
FAQ
Why do apps get rejected from the App Store?
Common reasons in Apple's guidelines include crashes or obvious bugs, placeholder content, no demo account for logins, metadata that does not match the app, an app that is little more than a website, and missing privacy or account-deletion features.
What crash rate is acceptable on Android?
Google's Android vitals thresholds are a user-perceived crash rate under 1.09% overall and under 8% per phone model; Play may reduce visibility if you exceed them.
Do I need to support tablets and foldables?
If your users have them, yes. Flexible layouts and tested window sizes make this far easier than adding it later.
How often will I need to update my app?
At least yearly to meet store requirements, and more often for fixes and security patches.
Does my app need account deletion?
On iOS, Apple requires that apps supporting account creation also offer account deletion within the app.
Sources
- Apple Developer, "App Review Guidelines": https://developer.apple.com/app-store/review/guidelines/
- Android Developers, "Android vitals": https://developer.android.com/topic/performance/vitals
- Android Developers, "Supporting different screen sizes": https://developer.android.com/guide/practices/screens_support
- OWASP, "Mobile Application Security Verification Standard (MASVS)": https://mas.owasp.org/MASVS/
