我正在构建一个 flutter 应用程序。我已经构建了一个带有构造函数的类。我制作了构造函数，因此我可以自定义我的 ListTile，因为我将此类用于多个页面，每次我都需要更改文本颜色，有时甚至添加一个 onTap 函数。

class AppList extends StatefulWidget {

  @override
    AppListState createState() => AppListState();

    AppList({Key key, this.child}) : super(key: key);

    final Widget child;

}

class AppListState extends State<AppList> {

  Widget child;

  List<Map<String, String>> _installedApps;

  @override
    void initState() {
      super.initState();
    }

  getApps() {
    setState(() {
      installedApps = _installedApps;
      getApp();
    });
  }

  @override
    Widget build(BuildContext context) {

      if (installedApps == null)
        getApps();

      return ListView.builder( 
        itemCount: installedApps == null ? 0 : installedApps.length,
        itemBuilder: (context, index) {
          return child; //This is where the ListTile will go. 
        },
      );
    }

}

//Just in case you were confused, I used a plugin for some of the features

在我构建这个类之后，我将它放在我的示例类中。

示例类:

class Example extends StatefulWidget {

  @override 
    ExampleState createState() => ExampleState();

}

class ExampleState extends State<Example> {

  @override
    Widget build(BuildContext context) {
      return MaterialApp (
        debugShowCheckedModeBanner: false,
        home: Scaffold (
          body: Container (
            color: Colors.black,
            child: AppList (
              child: ListTile ( 
                title: Text(installedApps[index]["app_name"]) //this is the text
              ),
            )
          )  
        ),
      );
    }

} 

然后，我在其中添加了一个 ListTile 和一个文本。但是当我在写文字时，我意识到我无法输入我想要的文字。这是因为 Example 类中没有定义 'index'。

有什么好的方法可以将此文本放入我的示例类中吗？

完整代码:

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

import 'dart:async';
import 'dart:io';

import 'package:flutter_appavailability/flutter_appavailability.dart';

void main() {
  SystemChrome.setEnabledSystemUIOverlays([]);
  runApp(Example());
}

Future<void> getApp() async {

  if (Platform.isAndroid) {

    installedApps = await AppAvailability.getInstalledApps();

    print(await AppAvailability.checkAvailability("com.android.chrome"));

    print(await AppAvailability.isAppEnabled("com.android.chrome"));

  }
  else if (Platform.isIOS) {
    installedApps = iOSApps;

    print(await AppAvailability.checkAvailability("calshow://"));

  }

}

List<Map<String, String>> installedApp;
List<Map<String, String>> installedApps;
List<Map<String, String>> iOSApps = [
  {
    "app_name": "Calendar",
    "package_name": "calshow://"
  },
  {
    "app_name": "Facebook",
    "package_name": "fb://"
  },
  {
    "app_name": "Whatsapp",
    "package_name": "whatsapp://"
  }
];

class Example extends StatefulWidget {

  @override 
    ExampleState createState() => ExampleState();

}

class ExampleState extends State<Example> {

  @override
    Widget build(BuildContext context) {
      return MaterialApp (
        debugShowCheckedModeBanner: false,
        home: Scaffold (
          body: Container (
            color: Colors.black,
            child: AppList ()
          )  
        ),
      );
    }

}

class AppList extends StatefulWidget {

  @override
    AppListState createState() => AppListState();

  AppList({Key key, this.child}) : super(key: key);

  final Widget child;

}

class AppListState extends State<AppList> {

  Widget child;

  List<Map<String, String>> _installedApps;

  @override
    void initState() {
      super.initState();
    }

  getApps() {
    setState(() {
      installedApps = _installedApps;
      getApp();
    });
  }

  @override
    Widget build(BuildContext context) {

      if (installedApps == null)
        getApps();

      return ListView.builder( 
        itemCount: installedApps == null ? 0 : installedApps.length,
        itemBuilder: (context, index) {
          return ListTile (
            title: Text(installedApps[index]["app_name"])
          );
        },
     );
   }

}

最佳答案

您可以传递一个 builder 函数，而不是将 Widget 传递给您的自定义 AppList，该函数返回一个 Widget 并根据需要获取参数，例如索引和所需的任何配置。类似于以下内容:

函数定义:

typedef Widget MyListTileBuilder(int index);

然后更改以下内容:

final Widget child;

到

final MyListTileBuilder childBuilder;

当然你需要在示例类中实现你的builder方法:

Widget MyListTileBuilderImplementation (int index) {
  return ListTile ( 
                title: Text(installedApps[index]["app_name"]) //this is the text
              ),
}

当您在示例类中构建 AppList 时，您将传递该方法

AppList (
              childBuilder: MyListTileBuilderImplementation 
)

最后在 AppList 中调用构建器，而不是添加子小部件:

    itemBuilder: (context, index) {
      return childBuilder(index); //This is where the ListTile will go. 
    },

包含这些更改的完整代码如下所示(我不得不注释掉您未提供的引用):

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

import 'dart:async';
import 'dart:io';

//import 'package:flutter_appavailability/flutter_appavailability.dart';

typedef Widget MyListTileBuilder(int index);

void main() {
  SystemChrome.setEnabledSystemUIOverlays([]);
  runApp(Example());
}

Future<void> getApp() async {

  if (Platform.isAndroid) {

    //installedApps = await AppAvailability.getInstalledApps();

    //print(await AppAvailability.checkAvailability("com.android.chrome"));

    //print(await AppAvailability.isAppEnabled("com.android.chrome"));

  }
  else if (Platform.isIOS) {
    installedApps = iOSApps;

    //print(await AppAvailability.checkAvailability("calshow://"));

  }

}

List<Map<String, String>> installedApp;
List<Map<String, String>> installedApps=[
  {"app_name":"app1"},
  {"app_name":"app2"},
  {"app_name":"app3"},
];
List<Map<String, String>> iOSApps = [
  {
    "app_name": "Calendar",
    "package_name": "calshow://"
  },
  {
    "app_name": "Facebook",
    "package_name": "fb://"
  },
  {
    "app_name": "Whatsapp",
    "package_name": "whatsapp://"
  }
];

class Example extends StatefulWidget {

  @override 
    ExampleState createState() => ExampleState();

}

class ExampleState extends State<Example> {

  Widget MyListTileBuilderImplementation (int index) {
    return ListTile ( 
                  title: Text(installedApps[index]["app_name"] + "  index:" + index.toString()) //this is the text
                );
  }

  @override
    Widget build(BuildContext context) {
      return MaterialApp (
        debugShowCheckedModeBanner: false,
        home: Scaffold (
          body: Container (
            color: Colors.white,
            child: AppList (childBuilder: this.MyListTileBuilderImplementation)
          )  
        ),
      );
    }

}

class AppList extends StatefulWidget {

  @override
    AppListState createState() => AppListState();

  AppList({Key key, this.childBuilder}) : super(key: key);

  final MyListTileBuilder childBuilder;

}

class AppListState extends State<AppList> {

  List<Map<String, String>> _installedApps;

  @override
    void initState() {
      super.initState();
    }

  getApps() {
    setState(() {
      installedApps = _installedApps;
      getApp();
    });
  }

  @override
    Widget build(BuildContext context) {

      if (installedApps == null)
        getApps();

      return ListView.builder( 
        itemCount: installedApps == null ? 0 : installedApps.length,
        itemBuilder: (context, index) {
          return  widget.childBuilder(index);
        },
     );
   }

}

关于user-interface - 如何将Widget注入(inject)自定义子Widget并使用子Widgets迭代索引？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54035219/