Problem Statement
What is ProxyProvider and when would you use it? How does it handle dependencies between providers?
Explanation
ProxyProvider creates a provider that depends on other providers, useful when one model needs access to another model or service. For example, a CartModel might need access to ProductRepository to fetch product details. ProxyProvider rebuilds the dependent model whenever its dependencies change, maintaining consistency across related state.
Use ProxyProvider.builder with update parameter that receives previous instance and dependency values, returning new or updated instance. The provider automatically disposes the old instance if it's disposable. For multiple dependencies, use ProxyProvider2, ProxyProvider3, etc., each supporting more dependencies. This enables building complex dependency graphs where services depend on each other.
Common pattern: provide repositories and services with simple Provider, then use ProxyProvider for business logic models that need those services. For example, AuthService uses Provider, UserRepository uses Provider, and UserProfileModel uses ProxyProvider2 depending on both. This separates concerns - repositories handle data, services handle auth, and models handle business logic, all properly connected through ProxyProvider.
Be careful with circular dependencies - ProxyProvider can't handle A depending on B and B depending on A. Design your dependencies as a directed acyclic graph. The update function should be fast and pure, avoiding side effects or expensive operations. Consider if you really need ProxyProvider - sometimes passing dependencies through constructors is simpler for straightforward cases. Use ProxyProvider when dependencies are complex, change at runtime, or when proper dependency injection is needed.
