All the code you need to run Hello World in Flutter using a Stateless widget

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>IDECodeSnippetCompletionPrefix</key>
	<string>snippetAlert</string>
	<key>IDECodeSnippetCompletionScopes</key>
	<array>
		<string>All</string>
	</array>
	<key>IDECodeSnippetContents</key>
	<string>let alertController = UIAlertController(title: &lt;#T##String?#&gt;, message: &lt;#T##String?#&gt;, preferredStyle: &lt;#T##UIAlertController.Style#&gt;)
let firstAction = UIAlertAction(title: &lt;#T##String?#&gt;, style: .default, handler: &lt;#T##((UIAlertAction) -&gt; Void)?##((UIAlertAction) -&gt; Void)?##(UIAlertAction) -&gt; Void#&gt;)
let cancelAction = UIAlertAction(title: &lt;#T##String?#&gt;, style: .cancel, handler: nil)

alertController.addAction(firstAction)
alertController.addAction(cancelAction)
present(alertController, animated: true)</string>
	<key>IDECodeSnippetIdentifier</key>
	<string>8C458AD7-C631-457B-85CC-D2501E425D59</string>
	<key>IDECodeSnippetLanguage</key>
	<string>Xcode.SourceCodeLanguage.Swift</string>
	<key>IDECodeSnippetSummary</key>
	<string></string>
	<key>IDECodeSnippetTitle</key>
	<string>UIAlertController</string>
	<key>IDECodeSnippetUserSnippet</key>
	<true/>
	<key>IDECodeSnippetVersion</key>
	<integer>2</integer>
</dict>
</plist>

Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(title: Text('IntrinsicWidth')),
    body: Center(
      child: IntrinsicHeight(
        child: Row(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            RaisedButton(
              onPressed: () {},
              child: Text('Short'),
            ),
            RaisedButton(
              onPressed: () {},
              child: Text('A bit Longer'),
            ),
            RaisedButton(
              onPressed: () {},
              child: Text('The Longest text button'),
            ),
          ],
        ),
      ),
    ),
  );
}

products.sort((a,b) => a.compareTo(b));

sdk: ">=2.12.0 <3.0.0"


Then follow the steps:

Run flutter upgrade in the terminal to upgrade Flutter
Run dart migrate to run the dart migration tool.
Solve all errors which the migration tool shows.
Run flutter pub outdated --mode=null-safety to print all outdated packages.
Run flutter pub upgrade --null-safety to upgrade all packages automatically.
Check the code for errors and solve them (Very important).
Run dart migrate again and it should now be successful. Follow the link to checkout the proposed changes.
Press the "Apply Migration" button.
Check the code for errors again and fix them.

@IBAction func doSomething()
@IBAction func doSomething(sender: UIButton)
@IBAction func doSomething(sender: UIButton, forEvent event: UIEvent)

import 'package:flutter/material.dart';

void main() {
  runApp(
    new MaterialApp(
      title: 'Hello World App',
      home: new myApp(),
    )
  );
}

class myApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Hello World App'),
      ),
      body: new Center(
        child: new Text(
          'Hello, world!'
        ),
      ),
    );
  }
}

[[NSProcessInfo processInfo] operatingSystemVersion]

keytool -exportcert -list -v \
-alias <your-key-name> -keystore <path-to-production-keystore>

MaterialApp(
 debugShowCheckedModeBanner: false
)

Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(title: Text('IntrinsicWidth')),
    body: Center(
      child: IntrinsicWidth(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            RaisedButton(
              onPressed: () {},
              child: Text('Short'),
            ),
            RaisedButton(
              onPressed: () {},
              child: Text('A bit Longer'),
            ),
            RaisedButton(
              onPressed: () {},
              child: Text('The Longest text button'),
            ),
          ],
        ),
      ),
    ),
  );
}

<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"
        tools:ignore="ScopedStorage" />

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:angle="45"
        android:startColor="#ff00ff"
        android:endColor="#000000"/>
</shape>

// IntendedActivity - the file you wish to open
// CurrentActivity - the file where this code is placed  

Intent intent = new Intent (this, IntendedActivity.class);
    CurrentActivity.this.startActivity(intent);

public class LocalDatabase extends SQLiteOpenHelper {
         
    private static final String mDatabaseName = "LocalDatabase";
    private static final int mDatabaseVersion = 1;

public LocalDatabase(Context context) {
        super(context, mDatabaseName, null, mDatabaseVersion);
        SQLiteDatabase db = this.getWritableDatabase();
    }      

}

    AlarmManager alarmManager;