基於FutureBuilder通用網絡請求界面封裝

基於FutureBuilder通用網絡請求界面封裝

Dart異步編程Future

在Dart中，處理異步有兩種方式，一種方式是asyn/awiat ，另外一種方式就是FutureBuilder，FutureBuilder可以在網絡請求開始前，請求中，請求完成or失敗，幫助咱們管理咱們的UI界面。

FlutterBuilder源碼

///構造方法以及對應參數類型
const FutureBuilder({
    Key key,
    this.future,
    this.initialData,
    @required this.builder,
  }) : assert(builder != null), super(key: key);

final Future<T> future; //獲取數據異步操做
final AsyncWidgetBuilder<T> builder;//根據狀態返回不一樣widget


///ConnectionState四種狀態
enum ConnectionState {
  /// Not currently connected to any asynchronous computation.
  /// For example, a [FutureBuilder] whose [FutureBuilder.future] is null.
  none,
  /// Connected to an asynchronous computation and awaiting interaction.
  waiting,
  /// Connected to an active asynchronous computation.
  /// For example, a [Stream] that has returned at least one value, but is not
  /// yet done.
  active,
  /// Connected to a terminated asynchronous computation.
  done,
}
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FutureBuilder簡單使用Demo

FutureBuilder(
            future: fetchPost(),//網絡請求操做
            builder:
                (BuildContext context, AsyncSnapshot<CommonModel> snapshot) {
              switch (snapshot.connectionState) {
                case ConnectionState.none:
                  return Text("Input a url to connect");
                case ConnectionState.waiting:
                    //圓形加載widget
                  return Center(child: CircularProgressIndicator());
                case ConnectionState.active:
                  return Text("");
                case ConnectionState.done:
                  if (snapshot.hasError) {
                    return Text(
                      "${snapshot.error}",
                      style: TextStyle(color: Colors.red),
                    );
                  } else {
                    //正常數據返回回調
                    return Column(
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: <Widget>[
                        Text(
                          "網絡數據返回",
                          style: TextStyle(fontSize: 20),
                        ),
                        Text("title:${snapshot.data.title}"),
                        Text("icon:${snapshot.data.icon}"),
                        Text("url:${snapshot.data.url}"),
                      ],
                    );
                  }
              }
            })
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FutureBuilder簡單封裝

接下來開始咱們的通用網絡Widget封裝，根據Demo咱們發現須要一個能夠返回Future網絡請求方法，加載界面Widget，加載出錯的Widgwt以及網絡請求結束正常展現數據Widget。

框架思考須要實現功能：

• 請求網絡的方法 loadData
• 數據正常返回，給Widget界面賦值；
• 加載error Widget，網絡錯誤or無網狀態下，點擊錯誤Widget從新觸發網絡請求；
• 提供默認的loading 以及 error Widget，同時用戶也可自定義想要的提示界面；

開始實現功能

1.定義傳遞請求方法

///FutureBuilder的future傳的內容
typedef LoadDataFuture<T> = Future<T> Function(BuildContext context);
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2.定義抽象類（數據正常展現Widget）

abstract class NetNormalWidget<T> extends StatelessWidget {
  final T bean;//通用數據類

  NetNormalWidget({this.bean});

  @override
  Widget build(BuildContext context) {
    return buildContainer(bean);
  }
  ///給定義Widget賦值
  Widget buildContainer(T t);
}
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3.定義網絡出錯Widget以及對應點擊回調

///net出錯 回調
abstract class ErrorCallback {
  void retryCall();
}

///網絡請求 失敗 Widget
class NetErrorWidget extends StatelessWidget {
  final Widget errorChild;
  final ErrorCallback callback;

  NetErrorWidget({@required this.errorChild, this.callback});

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      child: errorChild,
      onTap: () => callback?.retryCall(),
    );
  }
}
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4.開始拼裝框架

///定義該框架須要屬性實現對應State
class FutureBuilderWidget<T> extends StatefulWidget {
  final Widget loadingWidget;
  final Widget errorWidget;
  final NetNormalWidget<T> commonWidget;

  final LoadDataFuture<T> loadData;

  FutureBuilderWidget(
      {@required this.commonWidget,
      @required this.loadData,
      this.loadingWidget,
      this.errorWidget});

  @override
  State<StatefulWidget> createState() => _FutureBuilderWidgetState<T>();
}
///實現State方法並mixins網絡出錯點擊回調
class _FutureBuilderWidgetState<T> extends State<FutureBuilderWidget<T>> with ErrorCallback {

  @override
  void initState() {
    super.initState();
    widget.loadData(context);
  }

  ///默認加載界面
  final defaultLoading = Center(
    child: CircularProgressIndicator(),
  );

  ///默認出錯界面
  Widget _defaultError(dynamic error) {
    return Center(
      child: Text(error.toString()),
    );
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
        future: widget.loadData(context),
        builder: (BuildContext context, AsyncSnapshot<T> snapshot) {
          switch (snapshot.connectionState) {
            case ConnectionState.none:
              break;
            case ConnectionState.waiting:
            case ConnectionState.active:
              return widget.loadingWidget ?? defaultLoading;
            case ConnectionState.done:
              if (snapshot.hasError) {
                ///網絡出錯
                if (widget.errorWidget != null) {
                  ///自定義出錯界面
                  if (widget.errorWidget is NetErrorWidget) {
                    return widget.errorWidget;
                  } else {
                    ///只自定義界面顯示內容
                    return NetErrorWidget(
                      errorChild: widget.errorWidget,
                      callback: this,
                    );
                  }
                } else {
                  ///選用默認出錯界面
                  return NetErrorWidget(
                    errorChild: _defaultError(snapshot.error),
                    callback: this,
                  );
                }
              }
              return widget.commonWidget.buildContainer(snapshot.data);
          }
        });
  }


  @override
  void retryCall() {
    widget.loadData(context);
    setState(() {
      ///通知State從新構建界面須要
    });
  }
}
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通用框架調用

class FutureBuilderDemo extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _FutureBuilderState();
}

class _FutureBuilderState extends State<FutureBuilderDemo> with ErrorCallback{
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("FutureBuilder控件封裝"),
      ),
      body: FutureBuilderWidget<CommonModel>(
        commonWidget: CommonWidget(),
        loadData: _loadData,
        //自定義出錯界面以及對應店家回調事件（本例子直接關閉界面）
// errorWidget: NetErrorWidget(
// callback:this,
// errorChild: Center(
// child: Text("網絡出錯 點擊返回"),
// ),
// ),
      ),
    );
  }
///網絡請求庫
 Future<CommonModel> _loadData(BuildContext context) async {
    Api.baseUrl = 'http://www.devio.org/io/flutter_app/';
    final resp = await HttpUtil.instance.fetchGet('json/test_common_model.json');
    return CommonModel.fromJson(resp);
  }

  @override
  void retryCall() {
    Navigator.of(context).pop();
  }
}
///實現抽象方法，直接給界面複製
class CommonWidget extends NetNormalWidget<CommonModel> {
  @override
  Widget buildContainer(CommonModel t) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Text(t.title),
          Text(t.icon),
        ],
      ),
    );
  }
}
複製代碼

Demo直接託管在Github具體目錄：./lib/demo/future_build_demo.dart

注：若有錯誤歡迎留言指正