Flutter學習-Stack練習 橫標製作

 import 'dart:math';

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

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

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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


  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    double w=180; //長條的寬度
    double h=64; //長條的高度

    //取出文字的大小
    final span=TextSpan(
      text: "這是橫標",
      style: TextStyle(fontSize: 20),
    );

    final tp=TextPainter(
      text: span,
      textDirection: TextDirection.rtl,)..layout();
    //依文字大小重新給予外部長條的長寬
    w=tp.width*2;
    h=tp.height;



    return Scaffold(

      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        //利用clipRRect裁切
        child: ClipRect(
          child: Stack(
            clipBehavior: Clip.none,
            children: [
              Container(
                color: Colors.red,
                width: 320,
                height: 320,
              ),
              Positioned(
                right: 0,
                //left: 0,
                top: sqrt(w*w/2-sqrt2*w*h+h*h),  //切成剛好大小的公式
                child: Transform.rotate(
                  alignment: Alignment.bottomRight,
                  angle: 45/180*pi, //由右方中間為0度， 前面為要轉的度數，後面是180*pi(轉成弧度制)
                  child: Container(
                    width: w,
                    height: h,
                    color: Colors.yellow,
                    alignment: Alignment.center,
                    child: Text.rich(span),
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}