flutter - 如何停止小部件以在Flutter的StatefulWidget类中的setState()方法上重新加载

Question

我试图实现的是保存小部件的状态，即在调用setState()方法时不应刷新它的状态。

class _GenderSelectionPageState extends State<GenderSelectionPage> {
  bool isFemaleSelected = false;
  AdmobBannerSize bannerSize;
  GlobalKey _globalKey = new GlobalKey();

  bool isLoaded = false;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    bannerSize = AdmobBannerSize.BANNER;
  }

  @override
  Widget build(BuildContext context) {
    double height = MediaQuery.of(context).size.height;
    double width = MediaQuery.of(context).size.width;

    return new Scaffold(
      body: new Container(
          width: width,
          child: new Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                Expanded(
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    mainAxisSize: MainAxisSize.max,
                    children: <Widget>[
                      Flexible(
                        child: new Hero(
                          tag: "gender",
                          child: Material(
                            child: new Row(
                              children: <Widget>[
                                InkWell(
                                  onTap: () {
                                    setState(() {
                                      if (isFemaleSelected) {
                                        isFemaleSelected = false;
                                      } else {
                                        isFemaleSelected = true;
                                      }
                                    });
                                  },
                                  child: Opacity(
                                    child: Image.asset(
                                      "assets/woman.png",
                                      height: height / 4,
                                      width: width / 2 - 12,
                                    ),
                                    opacity: isFemaleSelected ? 1.0 : 0.30,
                                  ),
                                ),
                                InkWell(
                                  onTap: () {
                                    setState(() {
                                      if (isFemaleSelected) {
                                        isFemaleSelected = false;
                                      } else {
                                        isFemaleSelected = true;
                                      }
                                    });
                                  },
                                  child: Opacity(
                                    opacity: !isFemaleSelected ? 1.0 : 0.30,
                                    child: Image.asset(
                                      "assets/boy.png",
                                      height: height / 4,
                                      width: width / 2 - 12,
                                    ),
                                  ),
                                ),
                              ],
                            ),
                          ),
                        ),
                      ),
                    ],
                  ),
                  flex: 1,
                ),
                InkWell(
                    onTap: () {
                      setState(() {

                      });
                      Navigator.push(
                          context,
                          MaterialPageRoute(
                              builder: (BuildContext) =>
                                  new HeightWeightSelection(isFemaleSelected
                                      ? "assets/woman.png"
                                      : "assets/boy.png")));
                    },
                    child: Container(
                      margin: EdgeInsets.only(bottom: 12.0),
                      child: new Image.asset(
                        "assets/next.png",
                        height: 64.0,
                        width: 64.0,
                      ),
                    )),
                new AdmobBannerWrapper(adUnitId: getBannerAdUnitId(),adSize: bannerSize,key: _globalKey,),
               /* new AdmobBanner(
                  adUnitId: getBannerAdUnitId(),
                  adSize: bannerSize,
                  listener:
                      (AdmobAdEvent event, Map<String, dynamic> args) {
                    handleEvent(event, args, 'Banner');
                  },
                ),*/
              ],
            ),
          )),
    );
  }

我不想每次我按下底部的图像按钮时都调用AdmobBannerWrapper.AdmobBannerWrapper应该只加载一次，但问题是每当我单击Next Image每次都加载AdmobBannerWrapper方法时。

Answer 1

用initState()构建它，然后在需要时使用它的引用，直到父窗口小部件重新初始化后，它才可以再次构建。

  var banner;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    bannerSize = AdmobBannerSize.BANNER;
    banner = AdmobBannerWrapper(adUnitId: getBannerAdUnitId(),adSize: bannerSize,key:_globalKey,);
  }

比在这里通过引用调用它 banner

  @override
  Widget build(BuildContext context) {
    double height = MediaQuery.of(context).size.height;
    double width = MediaQuery.of(context).size.width;

    return new Scaffold(
      body: new Container(
          width: width,
          child: new Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                Expanded(
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    mainAxisSize: MainAxisSize.max,
                    children: <Widget>[
                      Flexible(
                        child: new Hero(
                          tag: "gender",
                          child: Material(
                            child: new Row(
                              children: <Widget>[
                                InkWell(
                                  onTap: () {
                                    setState(() {
                                      if (isFemaleSelected) {
                                        isFemaleSelected = false;
                                      } else {
                                        isFemaleSelected = true;
                                      }
                                    });
                                  },
                                  child: Opacity(
                                    child: Image.asset(
                                      "assets/woman.png",
                                      height: height / 4,
                                      width: width / 2 - 12,
                                    ),
                                    opacity: isFemaleSelected ? 1.0 : 0.30,
                                  ),
                                ),
                                InkWell(
                                  onTap: () {
                                    setState(() {
                                      if (isFemaleSelected) {
                                        isFemaleSelected = false;
                                      } else {
                                        isFemaleSelected = true;
                                      }
                                    });
                                  },
                                  child: Opacity(
                                    opacity: !isFemaleSelected ? 1.0 : 0.30,
                                    child: Image.asset(
                                      "assets/boy.png",
                                      height: height / 4,
                                      width: width / 2 - 12,
                                    ),
                                  ),
                                ),
                              ],
                            ),
                          ),
                        ),
                      ),
                    ],
                  ),
                  flex: 1,
                ),
                InkWell(
                    onTap: () {
                      setState(() {

                      });
                      Navigator.push(
                          context,
                          MaterialPageRoute(
                              builder: (BuildContext) =>
                                  new HeightWeightSelection(isFemaleSelected
                                      ? "assets/woman.png"
                                      : "assets/boy.png")));
                    },
                    child: Container(
                      margin: EdgeInsets.only(bottom: 12.0),
                      child: new Image.asset(
                        "assets/next.png",
                        height: 64.0,
                        width: 64.0,
                      ),
                    )),
                banner, /*this is our variable */
               /* new AdmobBanner(
                  adUnitId: getBannerAdUnitId(),
                  adSize: bannerSize,
                  listener:
                      (AdmobAdEvent event, Map<String, dynamic> args) {
                    handleEvent(event, args, 'Banner');
                  },
                ),*/
              ],
            ),
          )),
    );
  }