Coordinator

Definition

The Coordinator (also called Router) is a component that handles navigation and screen flow in MVVM-C and MVC-C patterns. It separates navigation logic from ViewModels and Controllers.

flowchart TB
    subgraph Coordinator
        C[Coordinator]
    end
    
    C -->|creates| V1[View A]
    C -->|navigates| V2[View B]
    C -->|navigates| V3[View C]
    
    V1 -->|finish| C
    V2 -->|navigate to C| C

Responsibilities

• Navigation Management: Controls screen transitions and navigation stack
• View Creation: Creates and configures new Views/ViewControllers
• Deep Linking: Handles external URLs and navigation requests
• Coordination: Coordinates between multiple ViewModels/Controllers
• Flow Control: Manages conditional navigation (e.g., auth-gated flows)

Key Characteristics

• Single Responsibility: Only handles navigation
• Decoupled Navigation: ViewModels/Controllers don’t know about other screens
• Testable: Navigation logic can be tested independently
• Composable: Screens can be reused in different navigation flows

When to Use Coordinator

Use Coordinator pattern when:

• Navigation flows become complex
• Multiple ViewModels need to coordinate
• Deep linking is required
• A/B testing different flows

Coordinator in Different Patterns

Pattern	Coordinator Role
MVVM-C	Delegates navigation from ViewModel to Coordinator
MVC-C	Delegates navigation from Controller to Coordinator
VIPER	Router component acts as Coordinator

Common Implementations

// Coordinator example (pseudo-code)
class AppCoordinator {
  private navigationStack: NavigationStack
  
  fun showDashboard() {
    val vm = DashboardViewModel()
    val view = DashboardView(viewModel: vm)
    navigationStack.push(view)
  }
  
  fun showProfile(userId: String) {
    val vm = ProfileViewModel(userId: userId)
    val view = ProfileView(viewModel: vm)
    navigationStack.push(view)
  }
}

Child Coordinators

Coordinators can have child coordinators for nested navigation flows:

flowchart TB
    AC[App Coordinator]
    AC --> DC[Dashboard Coordinator]
    AC --> PC[Profile Coordinator]
    
    DC --> D1[Dashboard View]
    DC --> D2[Stats View]
    
    PC --> P1[Profile View]
    PC --> P2[Edit Profile View]

Related

• MVVM-C (Model View ViewModel Controller)
• MVC-C (Model View Controller Coordinator)
• VIPER (Router component)