flutter - Flutter:迭代期间的并发修改:'_GrowableList'的实例(长度:2)
问题描述
这是一个游戏,屏幕上随机出现一个小矩形,玩家必须点击它才能摆脱它,一个新的矩形将在屏幕的另一部分产生。我的代码有效,但每次点击我在屏幕上绘制的矩形时,都会出现以下错误。我该如何解决?
主要飞镖:
import 'dart:developer';
import 'package:flutter/material.dart';
import 'package:flame/flame.dart';
import 'package:flame/util.dart';
import 'package:flutter/services.dart';
import 'package:langaw/langaw-game.dart';
import 'package:flutter/gestures.dart';
void main() async {
WidgetsFlutterBinding.ensureInitialized();
Util flameUtil = Util();
await flameUtil.fullScreen();
await flameUtil.setOrientation(DeviceOrientation.portraitUp);
LangawGame game = LangawGame();
runApp(game.widget);
TapGestureRecognizer tapper = TapGestureRecognizer();
tapper.onTapDown = game.onTapDown;
flameUtil.addGestureRecognizer(tapper);
}
飞镖:
import 'dart:ui';
import 'package:flutter/cupertino.dart';
import 'package:langaw/langaw-game.dart';
class Fly {
Rect flyRect;
Paint flyPaint;
bool isDead = false, isOffScreen = false;
final LangawGame game;
// initialized with the game instance, along with positions x and y
Fly({this.game, double x, double y}) {
flyRect = Rect.fromLTWH(x, y, game.tileSize, game.tileSize);
flyPaint = Paint();
flyPaint.color = Color(0xff6ab04c);
}
// needs a render and update method
// this method will do the drawing
void render(Canvas canvas) {
canvas.drawRect(flyRect, flyPaint);
}
void update(double t) {
if (isDead) {
flyRect = flyRect.translate(0, game.tileSize * 12 * t);
if (flyRect.top > game.screenSize.height) {
isOffScreen = true;
}
}
}
void onTapDown() {
flyPaint.color = Color(0xffff4757);
isDead = true;
game.spawnFly();
}
}
langaw-game.dart:
import 'dart:ui';
import 'package:flame/game.dart';
import 'package:flame/flame.dart';
import 'package:langaw/components/fly.dart';
import 'dart:math';
import 'package:flutter/gestures.dart';
class LangawGame extends Game {
Size screenSize;
double tileSize;
List<Fly> flies;
Random rnd;
LangawGame() {
initialize();
}
void initialize() async {
flies = List<Fly>();
rnd = Random();
resize(await Flame.util.initialDimensions());
spawnFly();
}
// this method will do the drawing
void render(Canvas canvas) {
Rect bgRect = Rect.fromLTWH(0, 0, screenSize.width, screenSize.height);
Paint bgPaint = Paint();
bgPaint.color = Color(0xff576574);
canvas.drawRect(bgRect, bgPaint);
// now the flies are rendered on top of the background
flies.forEach((Fly fly) => fly.render(canvas));
// print(screenSize.toString());
}
void update(double t) {
flies.forEach((Fly fly) => fly.update(t));
flies.removeWhere((Fly fly) => fly.isOffScreen);
}
void spawnFly() {
double xPos = rnd.nextDouble() * (screenSize.width - tileSize);
double yPos = rnd.nextDouble() * (screenSize.height - tileSize);
flies.add(Fly(game: this, x: xPos, y: yPos));
}
void resize(Size size) {
screenSize = size;
tileSize = screenSize.width / 9;
}
void onTapDown(TapDownDetails d) {
flies.forEach((Fly fly) {
if (fly.flyRect.contains(d.globalPosition)) {
fly.onTapDown();
}
});
}
}
The following ConcurrentModificationError was thrown while handling a gesture:
Concurrent modification during iteration: Instance(length:2) of '_GrowableList'.
When the exception was thrown, this was the stack:
#0 List.forEach (dart:core-patch/growable_array.dart:286:36)
#1 LangawGame.onTapDown (package:langaw/langaw-game.dart:57:11)
#2 TapGestureRecognizer.handleTapDown.<anonymous closure> (package:flutter/src/gestures/tap.dart:463:51)
#3 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
#4 TapGestureRecognizer.handleTapDown (package:flutter/src/gestures/tap.dart:463:11)
...
Handler: "onTapDown"
Recognizer: TapGestureRecognizer#a4e24
state: possible
button: 1
解决方案
我今天在关注flutter游戏教程时遇到了同样的问题(BTW很好的教程,除了我认为这个小错误,我有时间会尽快发表评论)。
问题是 LangawGame.onTapDown 在苍蝇列表上进行迭代,并且在迭代期间调用 Fly.onTapDown() 在 spawnFly 方法中将元素添加到列表中。
所以列表在迭代时会被修改......恕我直言,这听起来像是一个错误。
简单的解决方案是使用 List.from 复制列表以进行迭代:即在 LangawGame 中:
void onTapDown(TapDownDetails d) {
List<Fly>.from(flies).forEach((Fly fly) {
if (fly.flyRect.contains(d.globalPosition)) {
fly.onTapDown();
}
});
有更多高性能的解决方案,但有更多的代码:)
推荐阅读
- flutter - Flutter - FocusNodes 和 Navigator 导致 TextField 失去装饰
- go - 如何在 UnmarshalJSON 中调用 json.Unmarshal 而不会导致堆栈溢出?
- python-3.x - Python Selenium - 脚本在关闭浏览器之前打开一个额外的窗口
- android - 目标 SDK 卡在 22
- go - cgo如何抑制警告
- android - SeekbarPreference 中的边距
- apache - spring boot 应用程序与 apache 负载平衡
- c# - Moq - 无法从 IGenericRepository 转换为 Generic Repository
- laravel-5 - Laravel 5.7 + 字体真棒
- c# - 循环通过设置列号(3)但长度可变的文本文档