如何防止对象在每次调用时都被重新初始化？-飞镖/颤振

Question

下面的代码片段：

class MainState extends State<Main>{

MusicMaterial musicObj = MusicMaterial();
SoundsMaterial soundObj = SoundsMaterial();

  @override
  Widget build(BuildContext context) {
    return Container(
          child: something.value == 0
              ? musicObj 
              : soundObj
        );
  }
}

class MusicMaterialState extends State<MusicMaterial>{
  @override
  Widget build(BuildContext context) {
    return Row(
          AnotherClass obj1 = AnotherClass(0, 'test'),  
          AnotherClass obj2 = AnotherClass(1, 'test'),
        );
  }
}

class AnotherClassState extends State<AnotherClass>{
import '../globals.dart' as globals;

@override
  void initState() {
    globals.globalCounter++;  // this variable is just a global variable from the globals.dart page
}

}

library my_prj.globals;

globalCounter = 0;

我尝试使用“automatickeepaliveClientMixin和@override bool get wantKeepAlive=>true”-即保持它活动，以便下次调用它时，它不会再次调用initState()，但是它没有工作。

Answer 1

希望我能正确地理解你需要什么。似乎您希望每个类类型的计数器只增加一次。我肯定有不同的方法来完成它，但我想到了让globalcounter稍微复杂一点

class GlobalCounter {
  List<String> _keys = List<String>();
  int _counter = 0;

  int get counter => _counter;

  void increaseCounter(String key) {
    // increase only if the key passed as parameter didn't increase already
    if (!_keys.contains(key)) {
      _counter++;
      _keys.add(key);
    }
  }
}

globalCounter = GlobalCounter();

那你可以这样用

@override
void initState() {
    // pass the type of the instance trying to increase the counter
    globals.globalCounter.increaseCounter(this.runtimeType.toString()); 
}