异常(exception):迭代期间的并发修改: '_GrowableList' 的实例(长度:17)

Question

我做游戏。在//ERROR ZONE 中称为异常。我不明白。类游戏有列表重新排列。

void spawnt(){
var rnd = new Random();
var rnd2 = new Random();
rnd = rnd.nextInt(100);
if(rnd2.nextBool())
  rnd2 = rnd2.nextInt(100);
else
  rnd2 = -rnd2.nextInt(100);
var x = flappy.position["x"]+lastx+sw+rnd;
var y = rnd2*pomer-100-1800*pomer-168*pomer;
Rectangle vrch = new Rectangle("img/tube1.png", sw, sh, {"x":x, "y":y, "z":0});
Rectangle spodek = new Rectangle("img/tube2.png", sw, sh, {"x":x, "y":sh+mezeray*pomer+y, "z":0});

vrch.onCollision((_){
  checkover();
});

spodek.onCollision((_){
  checkover();
});
game.addObject(spodek);
game.addObject(vrch);
var cp = new Checkpoint(sw, mezeray, {"x":x+sw, "y":y+sh, "z":0});
cp.onCollision((e){
  scoore++;
  querySelector("#scoore").text="SCOORE: ${scoore}";
  sounds[1].play();
  //THIS IS ERROR ZONE
  spawnt();
});
game.addObject(cp);

rnd = new Random();
rnd = rnd.nextInt(300);
rnd2 = new Random();
rnd2 = rnd2.nextInt(300);
var rnd3 = new Random();
rnd3 = new Random();
rnd3 = rnd3.nextInt(10);
Grab w;
if(rnd3 == 0 || rnd3 == 1 || rnd3 == 2){
  w = new Grab("img/cigarette.png", 600*pomer, 418*pomer, {"x":x+sw+rnd,"y":sh+mezeray*pomer+y-mezeray*pomer+rnd2-168*pomer, "z":0});
  w.scale(0.2);
  w.onCollision((c){
    smokescreen = true;
    smoketimer.cancel();
    smoketimer = new Timer(const Duration(milliseconds: 10000), (){
      smokescreen = false;
    });
    kucky.play();
    if(csong)
      cig.play();
    csong = false;
  });
  game.addObject(w);
}
else if(rnd3 == 3 || rnd3 == 4){
  w = new Grab("img/whiskey.png", 162*pomer, 398*pomer, {"x":x+sw+rnd,"y":sh+mezeray*pomer+y-mezeray*pomer+rnd2-168*pomer, "z":0});
  w.scale(0.2);
  w.onCollision((c){
    AudioElement pr = new AudioElement("sounds/yes.${koncovka}");
    pr.play();
    whiskey++;
    if(whiskey>=10 && whiskey<20){
      speedotoceni = 30;
      zhoupni();
    }
    else if(whiskey>=20 && whiskey<30){
      speedotoceni = 25;
      zhoupni();
    }
    else if(whiskey>=30 && whiskey<40){
      speedotoceni = 20;
      zhoupni();
    }
    else if(whiskey>=40 && whiskey<50){
      speedotoceni = 15;
      zhoupni();
    }
    else if(whiskey>=50 && whiskey<60){
     speedotoceni = 10;
      zhoupni();
    }
    else if(whiskey>=60 && whiskey<70){
      speedotoceni = 5;
      zhoupni();
    }
    else if(whiskey>=70 && whiskey<80){
      speedotoceni = 1;
      zhoupni();
    }
    querySelector("#scoore").text="SCOORE: ${scoore}";
  });
  game.addObject(w);
}
else if(rnd3 == 9){
  w = new Grab("img/jatra.png", 539*pomer, 521*pomer, {"x":x+sw+rnd,"y":sh+mezeray*pomer+y-mezeray*pomer+rnd2-168*pomer, "z":0});
  w.scale(0.1);
  w.onCollision((c){
    AudioElement pr = new AudioElement("sounds/yes.${koncovka}");
    pr.play();
    jatra++;
    document.cookie = "jatra=${jatra}; expires=Thu, 24 Dec 4000 00:00:00 GMT; path=/";
    querySelector("#jatracount").text = jatra.toString();
  });
  game.addObject(w);
 }
lastx = lastx+300*pomer+rnd;
}

类 Game.dart

  import 'dart:html';
  import 'dart:math';
  import 'dart:async';
  import 'Entity.dart';
  import 'Gravity.dart';
  import 'Rectangle.dart';
  import 'Camera.dart';
  import 'Checkpoint.dart';

  class Game {
    CanvasElement canvas;
    Gravity gravity;
    List<Entity> entities = new List();
    List<Rectangle> rectangles = new List();
    Camera camera;
    var leftSpace = 0;
    var topSpace = 0;
    var _onCollision;
    var _over = (_){};
    var _render = (_){};
    num _lastFrame = 0;
    bool isOver = false;


Game(this.canvas, this.gravity){
  window.animationFrame.then((e){this.render(e);});
}

void addEntity(Entity entita){
  this.entities.add(entita);
}

void addObject(Rectangle rectangle){
  this.rectangles.add(rectangle);
}

void render(num delta){
  num fps = 1000/(delta-this._lastFrame);
  this._lastFrame = delta;
  CanvasRenderingContext2D ctx = this.canvas.context2D;
  ctx.clearRect(0, 0, this.canvas.width+this.leftSpace.abs(), this.canvas.height+this.topSpace.abs());
  this._render(true);
  this.rectangles.forEach((s){
    ctx.fillStyle=s.color;
    if(s.hasColor()){
      ctx.fillStyle=s.color;
      ctx.fillRect(s.position["x"]-this.leftSpace,s.position["y"]-this.topSpace,s.width,s.height);
    }
    else{
      ctx.drawImageScaled(s.texture, s.position["x"]-this.leftSpace,s.position["y"]-this.topSpace,s.width,s.height);
    }
  });
  this.entities.forEach((e){
    e.move(fps);
    e.power["y"] += this.gravity.operate(e)*(60/fps);
    ctx.save(); 
    ctx.translate(e.position["x"]-this.leftSpace+e.width/2, e.position["y"]-this.topSpace+e.height/2);
    ctx.rotate(e.rotation* PI/180);
    ctx.drawImageScaled(e.img, -(e.width/2), -(e.height/2), e.width, e.height);
    ctx.restore(); 
  });
  collisionResponse();
  checkCollisions();
  if(!this.camera.fixed["x"])
    this.leftSpace = this.camera.target.position["x"]-this.canvas.width/2+this.camera.target.width/2;
  else
    this.leftSpace = this.camera.fixedPos["x"];

  if(!this.camera.fixed["y"])
    this.topSpace = this.camera.target.position["y"]-this.canvas.height/2+this.camera.target.height/2;
  else
    this.topSpace = this.camera.fixedPos["y"];
  this._render(false);
  ctx.closePath();
  window.animationFrame.then((e){this.render(e);});
}

void onCollision(e){
  this._onCollision = e;
}

void collisionResponse(){
  this.rectangles.forEach((s){
    num x1 = s.position["x"];
    num y1 = s.position["y"];
    num z1 = s.position["z"];
    num w1 = s.width;
    num h1 = s.height;

    this.entities.forEach((e){
      num rot = e.rotation * (PI / 180);
      num x2 = e.position["x"];
      num y2 = e.position["y"];
      num z2 = e.position["z"];
      num w2 = e.width;
      num h2 = e.height;
      if(x2>=x1-w2 && x2<=x1+w1 && y2>y1-h2 && y2<y1+h1 && z1==z2){
        s.collisionResponse(e);
        e.collision(s);
        s.collision(e);
      }
    });
  });
}

void checkCollisions(){
  List<Entity> kolize = new List();
  for(Entity e1 in this.entities){
    num x1 = e1.position["x"];
    num y1 = e1.position["y"];
    num z1 = e1.position["z"];
    num w1 = e1.width;
    num h1 = e1.height;

    for(Entity e2 in this.entities){
      if(e1 == e2 || (kolize.indexOf(e1) != -1 && kolize.indexOf(e2) != -1)) continue;
      num x2 = e2.position["x"];
      num y2 = e2.position["y"];
      num z2 = e2.position["z"];
      num w2 = e2.width;
      num h2 = e2.height;
      if(x2>=x1-w2 && x2<=x1+w1 && y2>y1-h2 && y2<y1+h1 && z1==z2){
        kolize.add(e1);
        kolize.add(e2);
      }
    }
  }
}

void over(){
  if(!this.isOver)
    this._over();
  this.isOver = true;
}

void onOver(e){
  this._over = e;
}

void onRender(f){
  this._render = f;
}
}

Uncaught Error :迭代期间的并发修改:“_GrowableList”的实例(长度:17)。
堆栈跟踪:
#0 List.forEach (dart:core-patch/growable_array.dart:241)

#1 Game.collisionResponse (FlappyBird/web/classes/Game.dart:83:28)

#2 Game.render (FlappyBird/web/classes/Game.dart:62:22)

#3 游戏渲染。 (FlappyBird/web/classes/Game.dart:75:47)

#4 _rootRunUnary (dart:async/zone.dart:717)

#5 _RootZone.runUnary (dart:async/zone.dart:854)

#6 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:439)

#7 _Future._propagateToListeners (dart:async/future_impl.dart:522)

#8 _Future._complete (dart:async/future_impl.dart:303)

#9 _SyncCompleter.complete (dart:async/future_impl.dart:44)

#10 Window.animationFrame。 (file:///E:/​​b/build/slave/dartium-win-full-stable/build/src/build/Release/obj/global_intermediate/blink/bindings/dart/dart/html/Window.dart:62 )

异常(exception):迭代期间的并发修改:“_GrowableList”的实例(长度:17)。
未定义(未定义:0:0)

够了吗？
有人知道如何修复它吗？
感谢您的回答。 :)

Answer 1

此错误意味着您在迭代期间正在从集合中添加或删除对象。这是不允许的，因为添加或删除项目会改变集合大小并扰乱后续迭代。

该错误可能来自您尚未发布源代码的以下行之一:

 s.collisionResponse(e);
 e.collision(s);
 s.collision(e);

我假设其中一个调用是在 forEach 期间从实体列表或矩形列表中删除一个项目，这是不允许的。相反，您必须重组代码以删除列表迭代之外的项目，可能使用 removeWhere 方法。

考虑以下从列表中删除奇数的尝试:

var list = [1, 2, 3, 4, 5];
list.forEach( (e) {
 if(e % 2 == 1) 
   list.remove(e);
});

这将失败并出现并发修改异常，因为我们尝试在列表迭代期间删除项目。

但是，在列表迭代期间，我们可以标记要删除的项目，然后使用 removeWhere 在批量操作中删除它们:

var list = [1, 2, 3, 4, 5];
var toRemove = [];

list.forEach( (e) {
 if(e % 2 == 1) 
   toRemove.add(e);
});

list.removeWhere( (e) => toRemove.contains(e));