Flutter Zone异常处理方法及基本原理

Zone myZone = Zone.current.fork(...)

Zone firstZone = Zone.current
    .fork(specification: zoneSpecification, zoneValues: {"name": "bob"});
Zone secondZone = firstZone.fork(zoneValues: {"extra_values": 12345});
secondZone.run(() {
  print(secondZone["name"]); // bob
  print(secondZone["extra_values"]); // 12345
}

RunHandler? run,
RunUnaryHandler? runUnary,
RunBinaryHandler? runBinary,

typedef RunHandler = R Function<R>(
    Zone self, ZoneDelegate parent, Zone zone, R Function() f);​
typedef RunUnaryHandler = R Function<R, T>(
    Zone self, ZoneDelegate parent, Zone zone, R Function(T arg) f, T arg);​
typedef RunBinaryHandler = R Function<R, T1, T2>(Zone self, ZoneDelegate parent,
    Zone zone, R Function(T1 arg1, T2 arg2) f, T1 arg1, T2 arg2);

Zone secondZone = firstZone.fork(
    zoneValues: {"extra_values": 12345},
    specification: ZoneSpecification(
      run: <int>(self, parent, zone, f) {
        int output = f();
        return output;
      },
    ));

secondZone.run(body);// 执行
run: <int>(self, parent, zone, f) {
    // 1.
    print("before");
    int output = f();// 这里的f就是body，它是可执行的
    print("after");
    return output;
    // 2.
},

// 在body内部打印的
body internal Zone:195048515 // 
Root Zone:195048515 // 
first Zone:700091970
second Zone:707932504

secondZone.run(body);// 执行
​
run: <int>(self, parent, zone, f) {
    // 1.这里执行在Root Zone
    print("before");
    Function output = parent.run(self, () {
      // 这里执行在second Zone
      return f(); 
    });
    print("after");
    return output;
    // 2.
},

R runZoned<R>(R body(),
    {Map<Object?, Object?>? zoneValues,
    ZoneSpecification? zoneSpecification,
    @Deprecated("Use runZonedGuarded instead") Function? onError}) {

/// Runs [body] in a new zone based on [zoneValues] and [specification].
R _runZoned<R>(R body(), Map<Object?, Object?>? zoneValues,
        ZoneSpecification? specification) =>
    Zone.current
        .fork(specification: specification, zoneValues: zoneValues)
        .run<R>(body);

runZoned(() {
  print("body internal Zone:" + Zone.current.hashCode.toString());
  print("Root Zone:" + Zone.root.hashCode.toString());
});
​
// 打印结果
body internal Zone:253994638
Root Zone:1004225004

body internal Zone:44766141
Root Zone:44766141

void asyncFunction() {
  print('1');
  Future((){
    print('2');
  }).then((e) {
    print('3');
  });
  print('4');
}

print 1
创建一个Future，并扔到Event Queue末尾
print 4
// 从Event Queue中取出，并执行下一个消息......
执行Future构造函数中的方法：->  print 2
print 2执行完成，即Future完成，回调它的then: ->  print 3

void asyncFunction() async {
  print('1');
  await Future(() {
    print('2');
  })；
  print('3');
  print('4');
}

print 1；
创建一个Future@1，并扔到Event Queue末尾；
// 从Event Queue中取出，并执行下一个消息......
取出Future@1，立刻执行它构造中的方法: -> print 2；
并将之后的代码打包，重新放到Event Queue的末尾（这里一般会等待IO完成，之后就会去执行和这个回调）
执行完成之后，执行之后的代码：
print 3;
print 4;

// Zone.run(()=>throwExceptionFunctino());
void throwExceptionFunction() {
  try {
    Future.delayed(const Duration(seconds: 1))
        .then((e) => throw("This is an Exception"));
  } catch (e) {
    print("an Exception has been Captured: ${e.toString()}");
  }
}

Unhandled exception:
This is an Exception
#0      throwExceptionFunction.<anonymous closure> (file:///Users/rEd/ideaProjects/dartProjs/zone/bin/zone.dart:140:22)
#1      _rootRunUnary (dart:async/zone.dart:1434:47)
#2      _CustomZone.runUnary (dart:async/zone.dart:1335:19)
<asynchronous suspension>

void throwExceptionFunction() async{
  try {
    await Future.delayed(const Duration(seconds: 1))
        .then((e) => throw ("This is an Exception"));
  } catch (e) {
    print("an Exception has been Captured: ${e.toString()}");
  }
}

an Exception has been Captured: This is an Exception
Process finished with exit code 0

void main() {
  runZoned(() => runApp(const MyExceptionApp()),
      zoneSpecification: ZoneSpecification(
          // print: (self, parent, zone, line) {},
          handleUncaughtError: (Zone self, ZoneDelegate parent, Zone zone,
              Object error, StackTrace stackTrace) {
            // 同样将print代理给上层Zone，这样就可以在上层捕获到这些异常了。
            parent.print(self," ### \n $stackTrace \n ### ");
          }));
}

floatingActionButton: FloatingActionButton(
  onPressed: () => Future((){
    throw ("ERROR!");
  }),
),

// runZonedGuarded替换runZoned
runZonedGuarded(() => runApp(const MyExceptionApp()),
    (Object error, StackTrace stack) {
  print('stack: $stack');
});