view_model 0.5.0-dev.12

view model for flutter. Simple and Lightweight & Cross - Widget Sharing & Automatic Resource Disposal

0.5.0

• Breaking Change & API Refinement: Major overhaul of ViewModel access methods to clarify responsibilities and improve predictability.
  • watchViewModel / readViewModel:
    • Now primarily responsible for creating new ViewModel instances.
    • The factory parameter is now mandatory.
    • Behavior depends on the provided factory:
      • If the factory includes a key, the instance is created and cached (or retrieved if already cached).
      • If the factory has no key, a new, non-shared instance is created every time.
  • New Methods for Cached Access:
    • Introduced watchCachedViewModel and readCachedViewModel to explicitly find existing, cached ViewModel instances by key or tag.
    • Introduced maybeWatchCachedViewModel and maybeReadCachedViewModel for safely accessing cached instances without throwing errors if not found.
  • Migration Guide:
    • To create/watch a new instance: Continue using watchViewModel but you must provide a factory.
    • To find an existing instance: Replace watchViewModel(key: ...) with watchCachedViewModel(key: ...) or readCachedViewModel(key: ...).
• support ViewModel-to-ViewModel Access
• Breaking change: The key parameter in watchViewModel, readViewModel, and ViewModel.read has been changed from String? to Object?. This allows for the use of custom objects as keys, but requires proper implementation of == and hashCode for custom key objects.

ViewModels can access other ViewModels using readViewModel and watchViewModel:

• readViewModel: Access another ViewModel without reactive connection
• watchViewModel: Create reactive dependency - automatically notifies when the watched ViewModel changes

When a ViewModel (the HostVM ) accesses another ViewModel (the SubVM ) via watchViewModel , the framework automatically binds the SubVM 's lifecycle to the HostVM 's UI observer (i.e., the State object of the StatefulWidget ).

This means both the SubVM and the HostVM are directly managed by the lifecycle of the same State object. When this State object is disposed, if neither the SubVM nor the HostVM has other observers, they will be disposed of together automatically.

This mechanism ensures clear dependency relationships between ViewModels and enables efficient, automatic resource management.

class UserProfileViewModel extends ViewModel {
  void loadData() {
    // One-time access without listening
    final authVM = watchCachedViewModel<AuthViewModel>();
    if (authVM?.isLoggedIn == true) {
      _fetchProfile(authVM!.userId);
    }
  }

  void setupReactiveAuth() {
    // Reactive access - auto-updates when auth changes
    final authVM = watchCachedViewModel<AuthViewModel>();
    // This ViewModel will be notified when authVM changes
  }


  void manualListening() {
    final authVM = watchCachedViewModel<AuthViewModel>();
    // You can also manually listen to any ViewModel
    authVM?.listen(() {
      // Custom listener logic
      _handleAuthChange(authVM);
    });
  }
}

0.4.7

• fix ViewModel.read

0.4.6

• The view_model package includes a powerful DevTools extension that provides real-time monitoring and debugging capabilities for your ViewModels during development.
• create devtools_options.yaml in root directory of project.

description: This file stores settings for Dart & Flutter DevTools.
documentation: https://docs.flutter.dev/tools/devtools/extensions#configure-extension-enablement-states
extensions:
  - view_model: true

• Breaking change: rename initConfig to initialize

0.4.5

• Add DefaultViewModelFactory for convenient and generic ViewModel factory creation.

0.4.4

• Add ViewModel.maybeRead

0.4.3

• Add maybeWatchViewModel and maybeReadViewModel
• update watchViewModel find logic

VM watchViewModel<VM extends ViewModel>({
  ViewModelFactory<VM>? factory,
  Object? key,
  Object? tag,
});

Parameter Name	Type	Optional	Description
factory	ViewModelFactory<VM>?	✅	Provides the construction method for the ViewModel. Optional; if an
			existing instance is not found in the cache, it will be used to create a new
			one.
key	String?	✅	Specifies a unique key to support sharing the same ViewModel instance.
			First, it tries to find an instance with the same key in the cache.
tag	Object?	✅	Add a tag for ViewModel instance. get tag by viewModel.tag. and it's
			used by find ViewModel by watchViewModel(tag:tag).

🔍 Lookup Logic Priority (Important) The internal lookup and creation logic of watchViewModel is as follows (executed in priority order):

1. If a key is passed in:

• First, attempt to find an instance with the same key in the cache.
• If a factory exists, use the factory to get a new instance.
• If no factory is found and no instance is found, an error will be thrown.

2. If a tag is passed in, attempt to find the latest created instance which has the same tag in the cache.
3. If nothing passed in, attempt to find the latest created instance of this type in the cache.

⚠️ If no ViewModel instance of the specified type is found, an error will be thrown. Ensure that the ViewModel has been correctly created and registered before use.

0.4.2

• Support find existing ViewModel by tag

set tag in ViewModelFactory.getTag():

class MyViewModelFactory extends ViewModelFactory<MyViewModel> {

  @override
  Object? getTag() {
    return 'tag';
  }
}

find existing ViewModel by tag:

late final MyViewModel viewModel;

@override
void initState() {
  super.initState();
  viewModel = watchViewModel<MyViewModel>(tag: 'tag');
}

0.4.1

Breaking change:

• Use recycleViewModel instead of refreshViewModel.

0.4.0

Breaking change:

• Use ViewModel instead of StatelessViewModel.

• Use StateViewModel instead of ViewModel.

• Use either watchViewModel or readViewModel instead of getViewModel/ requireExistingViewModel.

• Use StateViewModel.listenState instead of ViewModel.listen.

• Use ViewModel.listen instead of ViewModel.addListener.

• Support ViewModel.read<T> to read existing view model globally.

0.3.0

• transfer to https://github.com/lwj1994/flutter_view_model. thank to Miolin