3

我正在构建一个颤振应用程序。我已经构建了一个带有构造函数的类。我制作了构造函数，以便可以自定义我的 ListTile，因为我将此类用于多个页面，并且每次都需要更改文本颜色，有时甚至需要添加一个 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

在我建立了这个类之后，我把它放在了我的示例类中。

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。但是当我在写文本时，我意识到我无法写出我想要的文本。这是因为示例类中没有定义“索引”。

有没有一种好方法可以将此文本放入我的示例类中？

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"])
          );
        },
     );
   }

}
4

2 回答 2

1

除了将 Widget 传递给您的自定义 AppList，您还可以传递一个构建器函数，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，您需要在示例类中实现您的构建器方法：

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，您会传递该方法

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. 
    },

您具有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参考资料）：

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);
        },
     );
   }

}
于 2019-01-04T08:48:54.277 回答
0

这是您的修复代码：

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 (
            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"]}')
          );
        },
     );
   }

}

你试图给 title 一个表达式的值，而不仅仅是一个变量。您需要将其括在括号中。

这被认为是一个表达式，所以它必须这样写：

标题：文本（'${installedApps[index]["app_name"]}')

于 2019-01-04T08:43:41.387 回答