如何更新内置于 FutureBuilder 中的小部件 state

Question

之前，我使用ListBuilder生成一个包含 70 个数字的列表，它可以工作，但是将 70 个数字生成到自定义小部件中需要很长时间，而且当我点击一个数字只是为了更改背景颜色 state 时，需要几毫秒在更改 state 之前。

现在我使用FutureBuilder能够在等待生成的 70 个整数时加载屏幕。 但是当我点击球号时，背景颜色没有更新......就像setState()在 Future ListBuilder 中不起作用。

这个问题：“ Flutter - How to update state (or value?) of a Future/List used to build ListView (via FutureBuilder) ”非常相似，但它没有解决我的问题。

这是我在构建方法中的代码

Flexible(
                child:FutureBuilder<List<Widget>>(
                  future: ballNumbers,
                  builder: (context, snapshot){
                    if(snapshot.connectionState != ConnectionState.done){
                      return Center(child: CircularProgressIndicator());
                    }
                    if(snapshot.hasError){
                      return Center(child: Text("An error has occured"));
                    }
                    List<Widget> balls = snapshot.data ?? [];
                    return GridView.count(
                      crossAxisCount: 9,
                      children: balls,
                    );
                  }
                )

这是我为 function 启动 state 的方法：

Future<List<Widget>> ballNumbers;
List<int> picks = []; 

@override
void initState() {
    ballNumbers = getBallNumbers();
});

  Future<List<Widget>> getBallNumbers() async {
    return List.generate(limitBallNumber,(number){
      number = number + 1;
      return Padding(
        padding:EdgeInsets.all(2.5),
        child:Ball(
          number : number,
          size: ballWidth,
          textColor:(picks.contains(number)) ? Colors.black : Colors.white,
          ballColor: (picks.contains(number)) ? Style.selectedBallColor : Style.ballColor,
          onTap:(){
            setState((){
                picks.contains(number) ? picks.remove(number) : picks.add(number);
            });
          }
        )
      );
    });
  }

更新：这是 class Ball小部件

class Ball extends StatelessWidget {
  final Color ballColor;
  final Color textColor;
  final double size;
  final double fontSize;
  final int number;
  final VoidCallback onTap;

  Ball({Key key, @required this.number, 
    this.textColor, 
    this.ballColor,
    this.onTap,
    this.size = 55.0,
    this.fontSize = 14,
  }) : super(key : key);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: size,
      width: size,
      decoration: BoxDecoration(
        shape: BoxShape.circle,
        gradient: LinearGradient(
          colors: [
            Style.secondaryColor,
            ballColor != null ? ballColor : Style.ballColor,
          ],
          begin: Alignment.bottomLeft,
          end: Alignment.topRight
        )
      ),
      child: FlatButton(
        padding: EdgeInsets.all(0),
        child: Container(
          child: Text(
            number.toString().length > 1 ? number.toString() : "0" + number.toString(),
            style: TextStyle(
              fontSize: fontSize,
              color: textColor != null ? textColor : Colors.white
            ),
          ),
          padding: const EdgeInsets.all(4.0),
          decoration:BoxDecoration(
            color: Colors.transparent,
            border: Border.all(color: textColor != null ? textColor : Colors.white,  width: 1),
            borderRadius: BorderRadius.circular(32),
          )
        ),
        color: Colors.transparent,
        onPressed: onTap,
      ),
    );
  }
}

Answer 1

The issue is that getBallNumbers is only being called once in initState , so when picks is updated, it doesn't matter because getBallNumbers isn't called again to update the colors being passed to the Ball widgets.

一个简单的解决方法是在您的build中调用getBallNumbers与future: getBallNumbers() ，但这会导致CircularProgressIndicator在List重新生成时在每次单击时显示。

但是，理想情况下，您应该处理每个Ball的 state 内的所有颜色变化，这样您就不必在每次单击时都重新构建该List 。 并且要在父窗口小部件的State中维护所选数字的List ，您应该向每个球传递一个回调，以便在父窗口的List中添加和删除它们的数字。

---

粗略的例子：

球类（修改为有状态并删除了不必要的参数；活动的 state 现在存储在球中，而不是仅存储在父级中）：

class Ball extends StatefulWidget {
  final double size;
  final double fontSize;
  final int number;
  final VoidCallback toggleBall;
  final bool initialActiveState;

  Ball({Key key, @required this.number, 
    this.toggleBall,
    this.size = 55.0,
    this.fontSize = 14,
    this.initialActiveState,
  }) : super(key : key);

  _BallState createState() => _BallState();
}

class _BallState extends State<Ball> {
  bool isActive;
  
  @override
  void initState() {
    super.initState();
    isActive = widget.initialActiveState;
  }
  
  @override
  Widget build(BuildContext context) {
    return Container(
      height: widget.size,
      width: widget.size,
      decoration: BoxDecoration(
        shape: BoxShape.circle,
        gradient: LinearGradient(
          colors: [
            Style.secondaryColor,
            isActive ? Style.selectedBallColor : Style.ballColor,
          ],
          begin: Alignment.bottomLeft,
          end: Alignment.topRight
        )
      ),
      child: FlatButton(
        padding: EdgeInsets.all(0),
        child: Container(
          child: Text(
            widget.number.toString().length > 1 ? widget.number.toString() : "0" + widget.number.toString(),
            style: TextStyle(
              fontSize: widget.fontSize,
              color: isActive ? Colors.black : Colors.white,
            ),
          ),
          padding: const EdgeInsets.all(4.0),
          decoration:BoxDecoration(
            color: Colors.transparent,
            border: Border.all(color: isActive ? Colors.black : Colors.white,  width: 1),
            borderRadius: BorderRadius.circular(32),
          )
        ),
        color: Colors.transparent,
        onPressed: () {
          if(!isActive && widget.activeBallList.length >= 7) {
            return;
          }
          setState(() {
            isActive = !isActive;
          });
          widget.activeBallList.contains(widget.number) ? widget.activeBallList.remove(widget.number) : widget.activeBallList.add(widget.number);
        },
      ),
    );
  }
}

父类（唯一需要修改的是Ball的参数）：

Future<List<Widget>> getBallNumbers() async {
  return List.generate(limitBallNumber,(number){
    number = number + 1;
    return Padding(
      padding:EdgeInsets.all(2.5),
      child: Ball(
        number: number,
        size: ballWidth,
        initialActiveState: picks.contains(number),
        activeBallList: picks,
      )
    );
  });
}