Table of Contents

BLAZMVVM0006: ViewModelKey Consistency

Summary

ViewModelKey attribute values must be consistent with keys used in keyed navigation.

Severity

Warning - Inconsistent keys cause runtime navigation failures.

Why This Rule Exists

  • Ensures navigation keys match between View and ViewModel
  • Prevents runtime errors from key mismatches
  • Maintains consistency in keyed service resolution
  • Validates navigation configuration at compile time

✅ DO: Correct Usage

// ViewModel with key
[ViewModelDefinition(Key = "ProductDetails", Lifetime = ServiceLifetime.Transient)]
public class ProductViewModel : ViewModelBase
{
    [ViewParameter]
    public int ProductId { get; set; }
}

// Component with matching key
[ViewModelKey("ProductDetails")]
public class ProductPage : MvvmComponentBase<ProductViewModel>
{
    [Parameter]
    public int ProductId { get; set; }
}

// Navigation using the same key
public class NavigationService
{
    public void NavigateToProduct(int id)
    {
        _navigation.NavigateTo("ProductDetails", new { ProductId = id });
    }
}

❌ DON'T: Incorrect Usage

// ❌ Wrong: Key mismatch
[ViewModelDefinition(Key = "ProductDetails")]
public class ProductViewModel : ViewModelBase { }

[ViewModelKey("ProductDetail")]  // Missing 's' - won't match!
public class ProductPage : MvvmComponentBase<ProductViewModel> { }

// ❌ Wrong: Navigation uses different key
_navigation.NavigateTo("Product", parameters);  // Wrong key

// ❌ Wrong: Key defined but not used consistently
[ViewModelDefinition(Key = "MyKey")]
public class MyViewModel : ViewModelBase { }

// Component doesn't specify key - inconsistent
public class MyComponent : MvvmComponentBase<MyViewModel> { }

How to Fix

Match Keys Across All Uses

// Before
[ViewModelDefinition(Key = "OrderList")]
public class OrderViewModel : ViewModelBase { }

[ViewModelKey("Orders")]  // Different!
public class OrderComponent : MvvmComponentBase<OrderViewModel> { }

// After - Consistent everywhere
[ViewModelDefinition(Key = "Orders")]
public class OrderViewModel : ViewModelBase { }

[ViewModelKey("Orders")]
public class OrderComponent : MvvmComponentBase<OrderViewModel> { }

Benefits

Compile-Time Validation

// Catches key mismatches at compile time
[ViewModelKey("WrongKey")]  // Analyzer warning!
public class MyComponent : MvvmComponentBase<MyViewModel> { }

Refactoring Safety

// Change key in one place, analyzer shows all places to update
[ViewModelDefinition(Key = "NewKey")]  // Update here
public class MyViewModel : ViewModelBase { }

[ViewModelKey("OldKey")]  // Analyzer warns here!
public class MyComponent : MvvmComponentBase<MyViewModel> { }

Code Fix

This analyzer does not provide an automatic code fix. Manually update the key to match.

Additional Resources

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