我可以使用if更改小部件嗎？

例如

如果 TEXT = "text1' 而不是 page = mainpage()，

否則如果 TEXT = "text2' 而不是 page = mainpage2()，

和

如果 TEXT 是其他源代碼字串后各種

我怎樣才能接線：<

請幫幫我

額外的

class Categorylist extends StatefulWidget {
  @override
  _CategorylistState createState() => _CategorylistState();
}

class _CategorylistState extends State<Categorylist> {
  int selectedCategory = 0;
  List<String> categories = ["????", "?? ???", "?? ?? ???", "?? ?? ???", "?? ?? ????"];


  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.bottomCenter,
      margin: EdgeInsets.symmetric(vertical: kDefaultPadding / 2),
      height: 61,
      child: ListView.builder(
        scrollDirection: Axis.horizontal,
        itemCount: categories.length,
        itemBuilder: (context, index) => buildCategory(index, context),
      ),
    );
  }

  Padding buildCategory(int index, BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: kDefaultPadding),
      child: GestureDetector(
        onTap: () {
          setState(() {
            selectedCategory = index;
          });
        },
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            Text(
              categories[index],
              style: Theme.of(context).textTheme.bodyText1.copyWith(
                    fontWeight: FontWeight.w500,
                    color: index == selectedCategory
                        ? kTextColor
                        : Colors.black.withOpacity(0.4),
                  ),
            ),
            Container(
              margin: EdgeInsets.symmetric(vertical: kDefaultPadding / 2),
              alignment: Alignment.center,
              height: 6,
              width: 40,
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(10),
                color: index == selectedCategory
                    ? kSecondaryColor
                    : Colors.transparent,
              ),
            )
          ],
        ),
      ),
    );
  }
}

class ChangePage extends StatelessWidget {
  const ChangePage({Key? key}) : super(key: key);

  @override
    
  Widget build(BuildContext context) {
    return Scaffold(
      body: ChangeBody(),
    );
  }
}
class ChangeBody extends StatelessWidget {
  const ChangeBody({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return  Column(
      children: <Widget>[
        if (categories == '????') [
          ChangeBody() = mainpage()
        ]
        else (categories == '?? ???')[
        ChangeBody() = RegionJob()
        ],
      ],
    ),;
  }
}

這是我根據您的建議編輯的代碼，

但我需要更多幫助來插入我的 if 代碼

我的 if 代碼是 categories ,ChangeBody() = mainpage() 是紅線，

uj5u.com熱心網友回復：

Container(
          padding: EdgeInsets.all(8.0),
          height: 100,
          child: Row(
            children: [
             
              true
                  ? Text("No button")
                  : ElevatedButton(onPressed: () {}, child: Text("button"))
            ],
          ),
        )

要么

Container(
          padding: EdgeInsets.all(8.0),
          height: 100,
          child: Row(
            children: [
              
              if (true)
                Text("No button")
              else
                ElevatedButton(onPressed: () {}, child: Text("button")),
            ],
          ),
        )

要么

在 build 方法外宣告 mywidget 方法

Container(
          padding: EdgeInsets.all(8.0),
          height: 100,
          child: Row(
            children: [
              mywidget(),
             
            ],
          ),
        )

  mywidget() {
    if (true)
      return Text("No button");
    else
      return ElevatedButton(onPressed: () {}, child: Text("button"));
  }

要么

在構建方法之外宣告按鈕變數

  var button = true
      ? Text("No button")
      : ElevatedButton(onPressed: () {}, child: Text("button"));

Row(
            children: [
              mywidget(),
              button,
              true
                  ? Text("No button")
                  : ElevatedButton(onPressed: () {}, child: Text("button")),
              if (true)
                Text("No button")
              else
                ElevatedButton(onPressed: () {}, child: Text("button")),
            ],
          )

全碼

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

void main() {
  WidgetsFlutterBinding.ensureInitialized();

  runApp(MaterialApp(home: Mainwidget()));
}

class Mainwidget extends StatefulWidget {
  const Mainwidget({Key? key}) : super(key: key);

  @override
  _MainwidgetState createState() => _MainwidgetState();
}

class _MainwidgetState extends State<Mainwidget> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Container(
          padding: EdgeInsets.all(8.0),
          height: 100,
          child: Row(
            children: [
              mywidget(),
              button,
              true
                  ? Text("No button")
                  : ElevatedButton(onPressed: () {}, child: Text("button")),
              if (true)
                Text("No button")
              else
                ElevatedButton(onPressed: () {}, child: Text("button")),
            ],
          ),
        ),
      ),
    );
  }

 

  mywidget() {
    if (true)
      return Text("No button");
    else
      return ElevatedButton(onPressed: () {}, child: Text("button"));
  }

  var button = true
      ? Text("No button")
      : ElevatedButton(onPressed: () {}, child: Text("button"));
}

uj5u.com熱心網友回復：

你可以寫 if 條件如下

if(TEXT == "text1"){
    page = mainpage()
  }else if(TEXT == "text2"){
   page = mainpage2()
  }else{
    // set your code
  }

uj5u.com熱心網友回復：

方法一

if(TEXT == "text1) 
{
page = mainpage();
}
else {
page = mainpage2(); 
}

方法 2（使用 ? 運算子）

TEXT == "text" ?
page = mainpage() :
page = mainpage2();

uj5u.com熱心網友回復：

use switch case wrapped in builder method. Something like this


 enum Options { text1, text2 }
     Builder(
       builder: (context) {
         switch (option) {
            case Options.text1:
                  return Page1();
            case Options.text2:
                  return Page2();
            default:
                   return Page1();
                  }
                },
              ) 

uj5u.com熱心網友回復：

在小部件上使用 if else 條件的最佳方法是，

 Column(
    children: [
        if (yourCondition == true) ...[
          Text(""),
        ] else ...[
           Text(""),
        ],
    ],
 ),

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