blob: e28bec422efdd3c79abec78ced498a844950aa7c [file] [log] [blame]
// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'dart:async';
import 'dart:typed_data';
import 'dart:ui';
import 'package:flutter/foundation.dart';
/// A class that enables the dynamic loading of fonts at runtime.
/// The [FontLoader] class provides a builder pattern, where the caller builds
/// up the assets that make up a font family, then calls [load] to load the
/// entire font family into a running Flutter application.
class FontLoader {
/// Creates a new [FontLoader] that will load font assets for the specified
/// [family].
/// The font family will not be available for use until [load] has been
/// called.
: _loaded = false,
_fontFutures = <Future<Uint8List>>[];
/// The font family being loaded.
/// The family groups a series of related font assets, each of which defines
/// how to render a specific [FontWeight] and [FontStyle] within the family.
final String family;
/// Registers a font asset to be loaded by this font loader.
/// The [bytes] argument specifies the actual font asset bytes. Currently,
/// only TrueType (TTF) fonts are supported.
void addFont(Future<ByteData> bytes) {
if (_loaded)
throw StateError('FontLoader is already loaded');
(ByteData data) => Uint8List.view(data.buffer, data.offsetInBytes, data.lengthInBytes)
/// Loads this font loader's font [family] and all of its associated assets
/// into the Flutter engine, making the font available to the current
/// application.
/// This method should only be called once per font loader. Attempts to
/// load fonts from the same loader more than once will cause a [StateError]
/// to be thrown.
/// The returned future will complete with an error if any of the font asset
/// futures yield an error.
Future<void> load() async {
if (_loaded)
throw StateError('FontLoader is already loaded');
_loaded = true;
final Iterable<Future<void>> loadFutures =
(Future<Uint8List> f) => f.then<void>(
(Uint8List list) => loadFont(list, family)
return Future.wait(loadFutures.toList());
/// Hook called to load a font asset into the engine.
/// Subclasses may override this to replace the default loading logic with
/// custom logic (for example, to mock the underlying engine API in tests).
Future<void> loadFont(Uint8List list, String family) {
return loadFontFromList(list, fontFamily: family);
bool _loaded;
final List<Future<Uint8List>> _fontFutures;