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The truth about cross-platform development using Flutter, which saves you from the despair of “I want to run iOS and Android at the same time”
1. Introduction: The wall of “double implementation” that attacks engineers
If you're an engineer with experience developing mobile apps, you've probably wondered this question at least once."I want to make it compatible with both iOS and Android. However, writing two native versions (Swift/Kotlin) is too difficult in terms of resources. On the other hand, I cannot accept sloppy behavior such as using a web view."
Flutter is currently attracting the most attention as a powerful solution to this dilemma. However, simply saying "using Flutter will make things easier" will not solve the difficulties faced in the field.
Why is Flutter one of the "correct answers" for cross-platform? And how should they overcome the obstacles they encounter in actual battles? This time, from the perspective of a mid-career engineer, we will delve into the core of Flutter development and the inevitable technical aspects.
2. Redefining why “Flutter” instead of React Native
First of all, I would like to clarify the structural reasons why Flutter is currently being chosen among the many frameworks available.Many engineers tend to confuse them, but React Native and Flutter have fundamentally different approaches to solving "cross-platform" issues.
- React Native: Calls native components on the OS side via a JavaScript (TypeScript) bridge.
- Flutter: Has its own rendering engine called Skia (or the latest Impeller), which controls drawing on a pixel by pixel basis.
On the other hand, Flutter is closer to the idea of ``drawing directly on the canvas'' rather than borrowing UI components provided by the device's OS. For this reason, when implementing advanced custom UIs and effects, Flutter's strength is that it is overwhelmingly easier to achieve ``intended'' behavior.
3. The “Write Once, Run Anywhere” trap and the truth about MethodChannel
The magic phrase "Write the code once and it will work on both" is actually half true and half false.The most difficult part of cross-platform development is communicating with OS-specific features (camera, Bluetooth, notifications, background processing, etc.). These can hardly be completed with just Dart code.
This is where `MethodChannel` comes into play. It is a bridge for exchanging messages between Flutter and the native side, but if you neglect this, you will end up in a hellish debug loop where ``It works on iOS but behaves differently on Android.''
What you should avoid in practice is to rely on a generic plug-in and proceed without understanding its internal implementation. In particular, the following three points should be investigated and verified on your own.
1. Differences in Permissions: The writing rules and notification timing to users in iOS's `Info.plist` and Android's `AndroidManifest.xml` are completely different.
2. Differences in lifecycle: The behavior when an app goes to the background and the state restoration when restarting involves unique behavior (TaskManager, etc.) for each OS.
3. Push Notification: Even when using Firebase Cloud Messaging (FCM), the way tokens are handled and the control logic of notifications are often different between iOS APNs and Android FCM.
The skill of a senior engineer is how to abstract these ``portions that absolutely require native-specific processing'' and design them so that they can be handled as a common interface on the Dart side.
4. Practical code example: Separate platform-specific logic
For example, when ``obtaining device-specific information'' that requires different processing for each OS, it is standard practice to create an abstraction layer as shown below.// abstracts/device_info_service.dart
import 'package:flutter/foundation.dart';
/// An interface that abstracts device-specific information
abstract class DeviceInfoService {
String get deviceModel;
String get osVersion;
}
/// By defining common factories and abstract classes,
/// From the UI side, the specific implementation (iOS or Android) is not conscious.
class DeviceInfoProvider {
static DeviceInfoService get instance {
if (kIsWeb) {
return WebDeviceInfo(); // Implementation for web
}
// Inject the actual implementation here (it will be cleaner if you use a mechanism such as DI)
// By inserting an abstraction layer, the impact on the UI side is minimized.
return PlatformSpecificDeviceInfo();
}
}
// Implementation example (simple description)
class PlatformSpecificDeviceInfo implements DeviceInfoService {
@override
String get deviceModel => "Standard Model"; // Write the actual implementation here
@override
String get osVersion => "15.0";
}
// Implementation example for web environment
class WebDeviceInfo implements DeviceInfoService {
@override
String get deviceModel => "Web Browser";
@override
String get osVersion => "N/A";
}
In this way, maintenance costs can be dramatically reduced by completely isolating platform-specific differences from the UI and business logic layers.
5. Comparison with other technologies: for a sober choice
Here, we will organize the main technology stacks to be compared when selecting Flutter. You should choose based on ``what do you want to prioritize in the project'' rather than simply ``which one is better?''.| Technology Elements | Flutter (Dart) | React Native (JS/TS) | Kotlin Multiplatform (KMP) |
|---|---|---|---|
| Rendering | Own engine (Skia/Impeller) | Bridging native views | Using native UI of each language |
| Development speed | Very fast (Hot Reload) | Fast (Fast Refresh) | Medium (shared logic only) |
| UI consistency | Extremely high | Differences depending on the OS are likely to occur | Depends on the OS |
| Learning cost | Requires learning a new language (Dart) | Easy to learn if using the web system | Native knowledge is strongly required |
| Main uses | Advanced UI, high-speed prototypes | Reusing existing web assets, SNS systems | Large-scale development that prioritizes logic sharing |
6. “Hiccup points” in implementation and workarounds
I would like to share some of the major pitfalls that I encountered while actually working on the project. Just knowing this should save you several days of debugging time.① Differences between fonts and rendering
Fonts that can be used by default on Android may not be supported on iOS, or vice versa. Especially in a Japanese environment, certain characters may become "tofu (□)" or be replaced with an unintended font. The golden rule is to always include your own custom fonts in your projects to ensure consistency.② Image asset resolution
High-resolution images are managed using different folder structures, such as `drawable-xxhdpi` on Android and `@3x` on iOS. Flutter automatically handles these things, but it is essential to check that it looks good on both devices when preparing the material.③ Complexity of build and CI/CD
Even though it's called cross-platform, the deployment process is still different.- iOS: Xcode, Codematch, TestFlight
- Android: Gradle, Google Play Console
7. Summary: In the end, how should we face it?
If you view cross-platform development as a means to make things easier, you will inevitably run into a pitfall somewhere.
However, if you look at it as a way to abstract the complexities of different operating systems and unify core experiences, Flutter becomes a powerful weapon.
Ultimately, the most important thing in technology selection is determining where your team can allocate resources.
*If you are very particular about the UI and want to guarantee the same behavior on both OSes, use Flutter.
- If you are a lot of web engineers and want to make the most of your existing library assets, choose React Native.
- If you want to maintain 100% native feel and standardize the logic, use KMP.
After understanding this option correctly, take advantage of Flutter's powerful ecosystem (pub.dev) and solidify the "behind-the-scenes mechanisms" such as MethodChannel and CI/CD automation. This is the shortest route to stress-free cross-platform development.