setState无法正常工作。我做错了吗？

Question

导入'package：flutter / material.dart';

class MusicApp扩展了StatefulWidget {MusicApp（{Key key}）：super（key：key）;

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

class _MusicAppState扩展状态{字符串开始；布尔checkStart;地图cycleMap = {1：“ C”，2：“ C＃”，3：“ D”，4：“ D＃”，5：“ E”，6：“ F”，7：“ F＃”，8：“ G”，9：“ G＃”，10：“ A”，11：“ A＃”，12：“ B”};映射cycleeMap2;

列表周期= [“C”，“C＃”，“ D”，“ D＃”，“ E”，“F”，“F＃”，“G”，“G＃”，“一种”，“ A＃”];

字符串歌词=“ \ nMalai nasodh kaha dukcha ghau \ n \ nma je chu thikai chu bitholna naaaua”；

弦和=“ F G G＃G＃B＃F D＃C A＃F”；字符串chutia =“ Chutia”;列出doubleCycle;弦和弦变化; @override void initState（）{super.initState（）;doubleCycle =周期+周期；cycleeMap2 = cycleMap;

chordsChange =
    "${cycleMap[6]}   ${cycleMap[9]}   ${cycleMap[10]}        ${cycleMap[10]}   ${cycleMap[12]}         ${cycleMap[6]}\n\n

$ {cycleMap [12]} C A＃F“;}

@@ override Widget build（BuildContext context）{//以for（var i = 0; i

return ListView(
  children: <Widget>[
    // Stack(
    //   children: <Widget>[Text(chordsChange), Text(lyrics)],
    // ),
    FlatButton(
      child: Text("C"),
      onPressed: () {
        setState(() {
          doEverything();
        });
      },
    ),
    Text(chordsChange),
  ],
);   }

//对于第一个和弦，以获取数组int中的transposeIndex值transposeValue（String firstChord，String transposeTo）{int i = cycle.indexOf（firstChord）+1;

int transposeIndex = 0;
String transposeValue;

do {
  transposeValue = doubleCycle[i];

  transposeIndex++;
  if (transposeValue == transposeTo) {
    break;
  }

  i++;
} while (i <= doubleCycle.length - 1);

return transposeIndex;   }

//对于每个和弦，从上方导航到transposeIndex函数String newChord（int transposeIndex，StringcurrentCycleValue）{int i，计数器= 0；字符串transposeCycleValue;对于（i = cycle.indexOf（currentCycleValue）+1;i <= doubleCycle.length-1;i ++）{计数器+ = 1;if（counter == transposeIndex）{transposeCycleValue = doubleCycle [i];

    break;
  }
}
return transposeCycleValue;   }

void doEverything（）{int transposeValueIndex = transposeValue（start，“ C＃”）;cycleeMap2.forEach（（i，和弦）{字符串newValue = newChord（transposeValueIndex，和弦）;cycleMap [i] = newValue;}）; }}

Answer 1

不知道您要做什么，但我能发现的第一个错误是

class _MusicAppState extends State

应该是

class _MusicAppState extends State<MusicApp>