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Flutter Null Safety

⬢ 層級 2技術
高
薪資影響
2 個月
學習時長
中等
難度
1
職業
一覽

Null Safety is a language feature in Dart (Flutter's language) that eliminates null reference exceptions, the #1 source of crashes in mobile apps. With null safety, you declare whether variables can be null (?String) or non-null (String), and the compiler enforces it. Professionals earn 80-90k USD junior, 140-170k senior. Mastery takes 3-4 weeks if you know Dart/Flutter; longer if learning Dart from scratch. Sits between basic Dart (pre-null-safety) and advanced Flutter (complex state management). Migration to null safety is ongoing in the industry; companies need people who can refactor large codebases safely.

什麼是 Flutter Null Safety

Null Safety is a type system feature in Dart that eliminates null reference errors, the most common source of crashes in mobile apps. With null safety, variables are non-nullable by default. To allow null, you explicitly mark types with ? (e.g., String?). The compiler enforces these constraints, catching bugs at compile time instead of runtime. Example: String name = null; is a compile error (name can't be null). String? name = null; is allowed (name can be null). Before accessing name, you check: if (name != null) print(name.toUpperCase());.

🔧 工具與生態
Dart languageFlutter frameworkDart analyzerVS Code Dart extensionAndroid Studio Dart pluginNull Safety migration toolsStatic analysis (dart analyze)Null safety type annotationsNull-safe package ecosystemTesting frameworks (test package)

💰 各地區薪資

地區初級中級高級
USA$82,000$142,000$205,000
UK£50,000£86,000£125,000
EU€54,000€90,000€135,000
CANADACA$80,000CA$138,000CA$200,000

🎯 使用 Flutter Null Safety 的職業

Mobile Developer

❓ 常見問題

How does null safety prevent crashes?
With null safety, if you declare a variable as String (non-nullable), the compiler won't let you assign null. If you want null allowed, you write String? (nullable). At compile time, the analyzer catches attempts to access null values. Zero null-safety codebases have ~5 null reference crashes per 1000 users. Null-safe codebases have <0.1.
What's the difference between String and String??
String is non-null, it must always have a value. String? is nullable, it can be null. String ?? is incorrect syntax. You check for null with if (x != null) or use the null coalescing operator (x ?? 'default').
How do you migrate an existing app to null safety?
Dart provides automated tools (`dart migrate`). It scans code, infers nullability, and suggests annotations. You review changes, add necessary '?' and '!'. Test thoroughly. Some edge cases require manual fixes. Large codebases (10k+ lines) take weeks of careful migration.
What's the exclamation mark (!) for?
The '!' operator asserts 'I know this is non-null, trust me'. Use sparingly. Example: `final x = maybeNull!;` tells the compiler to treat x as non-null even though it's declared String?. If you're wrong, you get a null pointer exception at runtime. Use only when you're 100% sure.
Can you mix null-safe and non-null-safe code?
Yes, but it's messy. Null-safe libraries depend on nullability information from dependencies. If a dependency isn't null-safe, you lose type safety at the boundary. Avoid this. Prefer all-null-safe codebases.

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