Add Value Searchable Provider

[Ayad-Ben-Saliem]

Hello,

I'm trying to add a feature to use value searching for getting an object from Provider.

Description

When we create a new Provider, Provider registers the object that was created in the create method within BuildContext in the widget tree, then when we call read, watch, or of methods the Provider retrieves the value by searching backward in the widget tree (BY TYPE).
I'm trying to add a feature to search for an object by some condition in addition to the type.

Example

Current approach

Provider<Map<String, int>>(
    create: (context) => {'value1': 0},
    child: Provider<Map<String, int>>(
        create: (context) => {'value2': 10},
        child: Builder(
            builder: (context) {
                final val = context.read<Map<String, int>>();
                print(val);  // {'value2': 10}
            }
        ),
    ),
);

Suggestion approach

Provider<Map<String, int>>(
    create: (context) => {'value1': 0},
    child: Provider<Map<String, int>>(
        create: (context) => {'value2': 10},
        child: Builder(
            builder: (context) {
                final val = context.search<Map<String, int>>(
                    (Map<String, int> val) {
                        if(val.containsKey('value1') {
                            return true;
                        } else {
                            return false;
                        }
                    }
                );
                print(val);  // {'value1': 0}
            }
        ),
    ),
);

Can somebody help me to achieve this?

[rrousselGit]

Maybe you want to do:

 create: (context) => {...Provider.of<Map<String, int>>(context), 'value2': 10},

[Ayad-Ben-Saliem]

This can work, but it's inappropriate if value1 and value2 have nothing to do with each other.

Another thing, this will throw a ProviderNotFoundException if there is no type in the widget tree.
I want to implement the feature for any Object not only Map

Example

Looking for neerest person with age greater than or equal 18;
context.search<Person>((person) => person.age >= 18);

[Ayad-Ben-Saliem]

@rrousselGit

I'm still looking if my suggestion can be implemented within Provider.
This is will be highly beneficial for multiple cases.

1)- for Example:
I want to access two users which are registered over each other in the widget tree.

Provider<User>(
    create: (context) => User(name: 'User1'),
    child: Builder(
        builder: (context) {
            // Access user within the widget tree
            final user = context.read<User>();  // got User1
            ...
            ...
            ...
            return Provider<User>(
                create: (context) => User(name: 'User2'),
                child: Builder(
                    builder: (context) {
                    // Access user within the widget tree
                    final user = context.read<User>(); // got User2

                    // I can't access (User1) her from the widget tree using read, or of methods.
                    // so I need to search for it.
                    // I suggest a search method like this
                    // context.search<Type>(search method returns boolean value)

                    final user = context.search<User>(
                        (currentUser) {
                            // if this method returns true,
                            // the search method returns currentUser.
                            // else, looking for the next user object within the widget tree.
                            if (currentUser.name == 'User1') {
                                return true;
                            } else {
                                return false;
                            }
                        }
                    )
                )
            );
        }
    )
)

2)- Also. this method can decrease a lot of code duplication.

for example. In my project, I'm using the Bloc library and I have these Cubits
ItemNameCubit
ItemNumberCubit
ItemPriceCubit
ItemCostCubit
BillNumberCubit
BillExternalNumberCubit
ClientNameCubit
ClientNumberCubit
...

All these Cubits act the same as each other, where they extend from ValueCubit

abstract class ValueCubit<State> extends Cubit<State> {

    ValueCubit(State initialState) : super(initialState);

    set value(State value) {
        super.emit(value);
    }

    State get value => state;
}

if the search method was implemented, I can add a member in ValueCubit (Ex. String tag), and then I can register these Cubits with their names like this:

Provider(
    create: (context) => ValueCubit<String>(
        value: 'Test',
        tag: 'ItemName',
    );
),
Provider(
    create: (context) => ValueCubit<String>(
        value: '0',
        tag: 'ItemNumber',
    );
),
Provider(
    create: (context) => ValueCubit<String>(
        value: '123',
        tag: 'ItemExternalNumber',
    );
)

And when I want to access them (Ex. ItemNumber) I can do this:

final itemNumber = context.search<ValueCubit>( (valueCubit) => valueCubit.tag == 'ItemNumber' )

[Ayad-Ben-Saliem]

I have implemented the search mechanism in Provider, I edit the src/provider.dart like this:

...
static T of<T>(
    BuildContext context, {
    bool listen = true,
    bool Function(T value)? searchCallback,
  }) {
    assert(
    context.owner!.debugBuilding ||
        listen == false ||
        debugIsInInheritedProviderUpdate,
    '''
Tried to listen to a value exposed with provider, from outside of the widget tree.

This is likely caused by an event handler (like a button's onPressed) that called
Provider.of without passing `listen: false`.

To fix, write:
Provider.of<$T>(context, listen: false);

It is unsupported because may pointlessly rebuild the widget associated to the
event handler, when the widget tree doesn't care about the value.

The context used was: $context
''',
    );

    var inheritedElement = _inheritedElementOf<T>(context);

    T? value = inheritedElement?.value;
    _checkType(context, value);

    if (searchCallback != null) {
      do {
        if (inheritedElement == null)
          throw ProviderNotFoundException(T, context.widget.runtimeType);

        if (searchCallback(value as T)) {
          // Got a value
          if (listen) {
            // bind context with the element
            context.dependOnInheritedElement(inheritedElement);
          }
          break;
        }

        // Looking for another value
        inheritedElement = _inheritedElement2Of<T>(inheritedElement);
        value = inheritedElement?.value;
        _checkType(context, value);
      } while (true);
    } else {
      if (listen) {
        // bind context with the element
        // We have to use this method instead of dependOnInheritedElement, because
        // dependOnInheritedElement does not support relocating using GlobalKey
        // if no provider were found previously.
        context.dependOnInheritedWidgetOfExactType<_InheritedProviderScope<T?>>();
      }
    }

    return value as T;
  }



  /// Check wither [value] applies [T] type
  /// this check required only in SoundMode
  static _checkType<T>(BuildContext context, T? value) {
    if (_isSoundMode)
      if (value is! T)
        throw ProviderNullException(T, context.widget.runtimeType);
  }



  static _InheritedProviderScopeElement<T?>? _inheritedElementOf<T>(
      BuildContext context,) {
    // ignore: unnecessary_null_comparison, can happen if the application depends on a non-migrated code
    assert(context != null, '''
Tried to call context.read/watch/select or similar on a `context` that is null.

This can happen if you used the context of a StatefulWidget and that
StatefulWidget was disposed.
''');
    assert(
    _debugIsSelecting == false,
    'Cannot call context.read/watch/select inside the callback of a context.select',
    );
    assert(
    T != dynamic,
    '''
Tried to call Provider.of<dynamic>. This is likely a mistake and is therefore
unsupported.

If you want to expose a variable that can be anything, consider changing
`dynamic` to `Object` instead.
''',
    );

    final inheritedElement = context.getElementForInheritedWidgetOfExactType<_InheritedProviderScope<T?>>() as _InheritedProviderScopeElement<T?>?;

    if (inheritedElement == null && null is! T) {
      throw ProviderNotFoundException(T, context.widget.runtimeType);
    }

    return inheritedElement;
  }



  static _InheritedProviderScopeElement<T?>? _inheritedElement2Of<T>(
      _InheritedProviderScopeElement<T?> element,) {
    final inheritedElement = element.getElementForInheritedWidgetOfExactType<_InheritedProviderScope<T?>>() as _InheritedProviderScopeElement<T?>?;

    if (inheritedElement == null && null is! T) {
      throw ProviderNotFoundException(T, element.widget.runtimeType);
    }

    return inheritedElement;
  }
...

Also, I have added searchCallback to ReadContext.read and WatchContext.watch

T read<T>({bool Function(T)? searchCallback}) {
    return Provider.of<T>(this, listen: false, searchCallback: searchCallback);
}

T watch<T>({bool Function(T)? searchCallback}) {
    return Provider.of<T>(this, listen: true, searchCallback: searchCallback);
}

As well as, I have added a new SearchContext to implement context.search<T>

/// Exposes the [search] method.
extension SearchContext on BuildContext {
    T search<T>(bool Function(T) searchCallback, { bool listen = false }) {
    return Provider.of<T>(this, listen: listen, searchCallback: searchCallback);
    }
}