HeadlessThemeProvider#

Provides HeadlessTheme to descendant widgets.

Wrap your app (or a subtree) with this widget to make the theme available via HeadlessThemeProvider.of or HeadlessThemeProvider.themeOf.

Example:

HeadlessThemeProvider(
  theme: MyCustomTheme(),
  child: MaterialApp(...),
)

Constructors#

HeadlessThemeProvider() const#

const HeadlessThemeProvider({
  super.key,
  required this.theme,
  required super.child,
});

Properties#

hashCode no setter inherited#

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

external int get hashCode;

runtimeType no setter inherited#

A representation of the runtime type of the object.

Inherited from Object.

external Type get runtimeType;

theme final#

The theme to provide to descendants.

final HeadlessTheme theme;

Methods#

noSuchMethod() inherited#

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toString() inherited#

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

external String toString();

updateShouldNotify()#

@override
bool updateShouldNotify(HeadlessThemeProvider oldWidget) {
  return theme != oldWidget.theme;
}

Operators#

operator ==() inherited#

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

external bool operator ==(Object other);

Static Methods#

capabilityOf()#

Convenience method to get a required capability from the theme.

Combines themeOf + requireCapability in one call. This is the recommended way for components to access capabilities.

Example:

final renderer = HeadlessThemeProvider.capabilityOf<RButtonRenderer>(
  context,
  componentName: 'RTextButton',
);

static T capabilityOf<T>(
  BuildContext context, {
  required String componentName,
}) {
  final theme = themeOf(context);
  return requireCapability<T>(theme, componentName: componentName);
}

maybeCapabilityOf()#

Safe capability lookup.

• In debug/profile: asserts with a detailed, searchable error.
• In release: returns null (callers should render a fallback and report).

static T? maybeCapabilityOf<T>(
  BuildContext context, {
  required String componentName,
}) {
  final provider =
      context.dependOnInheritedWidgetOfExactType<HeadlessThemeProvider>();
  final theme = provider?.theme;
  if (theme == null) {
    assert(() {
      throw const MissingThemeException();
    }());
    return null;
  }
  final capability = theme.capability<T>();
  if (capability == null) {
    assert(() {
      throw MissingCapabilityException(
        capabilityType: T.toString(),
        componentName: componentName,
      );
    }());
    return null;
  }
  return capability;
}

of()#

Get the HeadlessTheme from the widget tree.

Returns null if no HeadlessThemeProvider is found. Prefer themeOf when you expect the theme to always be present.

static HeadlessTheme? of(BuildContext context) {
  final provider =
      context.dependOnInheritedWidgetOfExactType<HeadlessThemeProvider>();
  return provider?.theme;
}

themeOf()#

Get the HeadlessTheme from the widget tree.

Throws MissingThemeException if no HeadlessThemeProvider is found. Use this when the theme is required (most component use cases).

static HeadlessTheme themeOf(BuildContext context) {
  final theme = of(context);
  if (theme == null) {
    assert(() {
      throw const MissingThemeException();
    }());
    return const _MissingHeadlessTheme();
  }
  return theme;
}