Flutter

Question

标题基本上说明了一切。一个非常愚蠢的问题......我有这个基本代码来创建我的应用程序的初始状态：

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Some title'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {

    return new Scaffold(
      appBar: new AppBar(title: new Text(config.title)),
      body: new Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: [
          new InputWidget(),
        ]
      ),
    );
  }
}

现在，我如何在用户单击按钮时呈现新的 Widget？假设我想实例化另一个 InputWidget。

谢谢

Answer 1

您的构建函数是 "just code"，因此您可以使用类似

的方法动态构建传递给列的数组

var children = [];
children.add(new InputWidget());
if (_showAnother)
  children.add(new InputWidget());
...
  body: new Column(
    ...
    children: children,
...

...其中 _showAnother 是您在点击按钮时设置的某种布尔字段。

Answer 2

希望我能正确理解你的问题...

我认为要点是您不应该考虑 "another" 小部件 - 如果您将 MyHomePage 的内容从第一个 child 然后两个更改为您不真的保留第一个 child 然后 添加另一个 child。你只需先说 "I want one child" 然后你改变主意说 "I want two children".

在您的代码中，您通过在 _MyHomePageState 中调用 setState 来完成此操作。 Flutter 负责保留第一个并添加第二个 child.

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Some title'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  int count = 1;

  @override
  Widget build(BuildContext context) {
    List<Widget> children = new List.generate(count, (int i) => new InputWidget(i));

    return new Scaffold(
        appBar: new AppBar(title: new Text(widget.title)),
        body: new Column(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: children
        ),
        floatingActionButton: new FloatingActionButton(
          child: new Icon(Icons.add),
          onPressed: () {
            setState(() {
              count = count + 1;
            });
          },
        )
    );
  }
}

class InputWidget extends StatelessWidget {

  final int index;

  InputWidget(this.index);

  @override
  Widget build(BuildContext context) {
    return new Text("InputWidget: " + index.toString());
  }
}

你是这个意思吗？

Flutter - 单击时呈现新的小部件

Flutter - Render new Widgets on click

mobile

dart