Flutter Error: "Widget cannot build because is already in the process of building"

Question

我收到这个错误：

I/flutter (29346): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (29346): The following assertion was thrown building MainLogic(dirty, state: _MainLogic#9c794):
I/flutter (29346): setState() or markNeedsBuild() called during build.
I/flutter (29346): This InhWidget widget cannot be marked as needing to build because the framework is already in the
I/flutter (29346): process of building widgets. A widget can be marked as needing to be built during the build phase
I/flutter (29346): only if one of its ancestors is currently building. This exception is allowed because the framework
I/flutter (29346): builds parent widgets before children, which means a dirty descendant will always be built.
I/flutter (29346): Otherwise, the framework might not visit this widget during this build phase.
I/flutter (29346): The widget on which setState() or markNeedsBuild() was called was:
I/flutter (29346):   InhWidget(state: InhState#3aaa8)
I/flutter (29346): The widget which was currently being built when the offending call was made was:
I/flutter (29346):   MainLogic(dirty, state: _MainLogic#9c794)

在向您大量介绍代码之前，我想稍微解释一下背后的逻辑：我正在尝试执行百家乐游戏规则，为此，我设置了一个 Inherited 小部件，一些无状态小部件发送存储在继承状态中的对象的输入，根据此对象数据，其他小部件自行重建。

我做的最后一个改变是应用百家乐 "drawing rules", 可以使对象在需要时跳过输入，但是当发生这种情况时，继承的小部件不喜欢它。

我将 post 代码的最后一部分，但如果您认为有其他相关的问题，我会post。

提前感谢您的帮助

    class MainLogic extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => new _MainLogic();
}
class _MainLogic extends State<MainLogic> {
  Widget cardGrid = CardGrid();
  Widget newGame = NewGame();
  Rules rules;
  bool gameOver;
  @override
  void initState(){
    super.initState();
    gameOver = false;
  }
  @override
  Widget build(BuildContext context) {
    final InhState state = InhWidget.of(context);
    rules = new Rules(game:state.game);
    if(gameOver==false && state.game.count>3 && rules.playerExtraCard()==false)
    {state.skip();}
    if(gameOver==false && state.game.count>4 && rules.bankerExtraCard()==false)
    {state.skip();}
    checkGame(state.game.count);
    return Container(child:status(gameOver));
  }
  status(bool _gameOver) {
    Widget whichOne;
    if (_gameOver) {whichOne=newGame;}
    else {whichOne=cardGrid;}
    return whichOne;
  }
  void checkGame(int cards) {
    if (cards >= 6) {
      gameOver = true;
    } else {gameOver = false;}
  }

...

   class Rules {
  final Game game;
  Rules({this.game});
  static Deck deck = new Deck();
  int get p1 => deck.getValue(game.p1);
  int get p2 => deck.getValue(game.p2);
  int get p3 => deck.getValue(game.p3);
  int get b1 => deck.getValue(game.b1);
  int get b2 => deck.getValue(game.b2);
  int get b3 => deck.getValue(game.b3);
  normalize(List<int> input) {
    int normal;
    int initial = 0;
    input.forEach((num e){initial += e;});
    if(initial>9) {normal=initial-10;}
    else {normal=initial;}
    return normal;
  }
  playerExtraCard() {
    bool extraCard;
    int pInit = normalize([p1,p2]);
    int bInit = normalize([b1+b2]);
    if (pInit > 5) {extraCard = false;}
    else if (bInit > 7) {extraCard = false;}
    else {extraCard = true;}
    return extraCard;
  }
  bankerExtraCard() {
    bool extraCard;
    int pInit = normalize([p1,p2]);
    int bInit = normalize([b1+b2]);
    int pWing = normalize([p3]);
    if (pInit>7) {extraCard = false;}
    else if (bInit>6) {extraCard = false;}
    else if (pInit>5 && bInit<6) {extraCard = true;}
    else if (pInit<6 && bInit==6 && pWing<8 && pWing>5) {extraCard = true;}
    else if (pInit<6 && bInit==5 && pWing<8 && pWing>3) {extraCard = true;}
    else if (pInit<6 && bInit==4 && pWing<8 && pWing>1) {extraCard = true;}
    else if (pInit<6 && bInit==3 && pWing==8) {extraCard = true;}
    else if (pInit<6 && bInit<3) {extraCard = true;}
    else {extraCard = false;}
    return extraCard;
  }
}

...

   class InhState extends State<InhWidget> {
  Game game = new Game();
  @override
  void initState() {
    super.initState();
    game.blank();
  }
  void deal(String card) {
    setState(() {
      game.cards[game.count] = card;
      game.count = game.count + 1;
    });
  }
  void restart(){
    setState(() {
      game.blank();
    });
  }
  void skip() {
    setState(() {
      game.count = game.count + 1;
    });
  }
  @override
  Widget build(BuildContext context) {
    return new InhCore(
      data: this,
      child: widget.child,
    );
  }
}

...

   class InhWidget extends StatefulWidget {
  InhWidget({this.child});
  final Widget child;
  @override
  State<StatefulWidget> createState() => InhState();
  static InhState of(BuildContext context) {
    return (context.inheritFromWidgetOfExactType(InhCore) as InhCore).data;
  }
}

Answer 1

您在 build() 中调用 state.skip() 并在 skip()

中调用 setState()

  void skip() {
    setState(() {
      game.count = game.count + 1;
    });
  }

通常在 build() 中避免 "business logic" 是个好主意。

不需要计算您在 build() 中使用 InhState 所做的所有事情。 build() 可以在不同时间经常调用。

您应该根据用户交互事件 (onTap:, ...) 或其他事件源（如指示异步操作的状态更改的流或期货）来更新状态。

Answer 2

我支持@Günter Zöchbauer 的回答并按照他的建议重构代码，但为了更快地修复，您可以尝试将 state.skip(); 指令（build() 内的指令）包装到一个WidgetsBinding.instance.addPostFrameCallback。这样您就可以将状态更改操作推迟到构建之后立即发生。

@override
Widget build(BuildContext context) {
  final InhState state = InhWidget.of(context);
  rules = new Rules(game:state.game);
  if (!gameOver) {
    if (state.game.count > 3 && !rules.playerExtraCard() ||
        state.game.count > 4 && !rules.bankerExtraCard())
    {
      WidgetsBinding.instance.addPostFrameCallback((_) {
        state.skip();
      });
    }
  }

  checkGame(state.game.count);
  return Container(child:status(gameOver));
}

无关，但我也建议您在项目中使用 flutter format 来帮助您调整代码风格。

Flutter Error: "Widget cannot build because is already in the process of building"

Flutter Error: "Widget cannot build because is already in the process of building"

widget

flutter

inherited-widget