361 lines
9.1 KiB
Markdown
361 lines
9.1 KiB
Markdown
# 持久化实体
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> **版本**: v2.3.0+
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持久化实体（Persistent Entity）是一种可以在场景切换时自动迁移到新场景的特殊实体。适用于需要跨场景保持状态的游戏对象，如玩家、游戏管理器、音频管理器等。
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## 基本概念
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在 ECS 框架中，实体有两种生命周期策略：
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| 策略 | 说明 | 默认 |
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|-----|------|------|
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| `SceneLocal` | 场景本地实体，场景切换时销毁 | ✓ |
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| `Persistent` | 持久化实体，场景切换时自动迁移 | |
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## 快速开始
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### 创建持久化实体
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```typescript
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import { Scene } from '@esengine/ecs-framework';
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class GameScene extends Scene {
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protected initialize(): void {
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// 创建持久化玩家实体
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const player = this.createEntity('Player').setPersistent();
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player.addComponent(new Position(100, 200));
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player.addComponent(new PlayerData('Hero', 500));
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// 创建普通敌人实体（场景切换时销毁）
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const enemy = this.createEntity('Enemy');
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enemy.addComponent(new Position(300, 200));
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enemy.addComponent(new EnemyAI());
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}
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}
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```
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### 场景切换时的行为
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```typescript
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import { Core, Scene } from '@esengine/ecs-framework';
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// 初始场景
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class Level1Scene extends Scene {
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protected initialize(): void {
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// 玩家 - 持久化，会迁移到下一个场景
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const player = this.createEntity('Player').setPersistent();
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player.addComponent(new Position(0, 0));
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player.addComponent(new Health(100));
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// 敌人 - 场景本地，切换时销毁
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const enemy = this.createEntity('Enemy');
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enemy.addComponent(new Position(100, 100));
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}
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}
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// 目标场景
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class Level2Scene extends Scene {
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protected initialize(): void {
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// 新的敌人
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const enemy = this.createEntity('Boss');
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enemy.addComponent(new Position(200, 200));
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}
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public onStart(): void {
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// 玩家已自动迁移到此场景
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const player = this.findEntity('Player');
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console.log(player !== null); // true
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// 位置和血量数据完整保留
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const position = player?.getComponent(Position);
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const health = player?.getComponent(Health);
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console.log(position?.x, position?.y); // 0, 0
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console.log(health?.value); // 100
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}
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}
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// 切换场景
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Core.create({ debug: true });
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Core.setScene(new Level1Scene());
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// 稍后切换到 Level2
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Core.loadScene(new Level2Scene());
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// Player 实体自动迁移，Enemy 实体被销毁
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```
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## API 参考
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### Entity 方法
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#### setPersistent()
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将实体标记为持久化，场景切换时不会被销毁。
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```typescript
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public setPersistent(): this
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```
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**返回**: 返回实体本身，支持链式调用
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**示例**:
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```typescript
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const player = scene.createEntity('Player')
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.setPersistent();
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player.addComponent(new Position(100, 200));
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```
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#### setSceneLocal()
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将实体恢复为场景本地策略（默认）。
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```typescript
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public setSceneLocal(): this
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```
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**返回**: 返回实体本身，支持链式调用
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**示例**:
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```typescript
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// 动态取消持久化
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player.setSceneLocal();
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```
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#### isPersistent
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检查实体是否为持久化实体。
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```typescript
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public get isPersistent(): boolean
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```
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**示例**:
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```typescript
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if (entity.isPersistent) {
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console.log('这是持久化实体');
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}
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```
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#### lifecyclePolicy
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获取实体的生命周期策略。
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```typescript
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public get lifecyclePolicy(): EEntityLifecyclePolicy
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```
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**示例**:
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```typescript
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import { EEntityLifecyclePolicy } from '@esengine/ecs-framework';
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if (entity.lifecyclePolicy === EEntityLifecyclePolicy.Persistent) {
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console.log('持久化实体');
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}
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```
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### Scene 方法
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#### findPersistentEntities()
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查找场景中所有持久化实体。
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```typescript
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public findPersistentEntities(): Entity[]
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```
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**返回**: 持久化实体数组
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**示例**:
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```typescript
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const persistentEntities = scene.findPersistentEntities();
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console.log(`场景中有 ${persistentEntities.length} 个持久化实体`);
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```
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#### extractPersistentEntities()
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提取并从场景中移除所有持久化实体（通常由框架内部调用）。
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```typescript
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public extractPersistentEntities(): Entity[]
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```
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**返回**: 被提取的持久化实体数组
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#### receiveMigratedEntities()
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接收迁移过来的实体（通常由框架内部调用）。
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```typescript
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public receiveMigratedEntities(entities: Entity[]): void
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```
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**参数**:
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- `entities` - 要接收的实体数组
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## 使用场景
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### 1. 玩家实体跨关卡
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```typescript
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class PlayerSetupScene extends Scene {
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protected initialize(): void {
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// 玩家在所有关卡中保持状态
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const player = this.createEntity('Player').setPersistent();
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player.addComponent(new Transform(0, 0));
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player.addComponent(new Health(100));
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player.addComponent(new Inventory());
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player.addComponent(new PlayerStats());
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}
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}
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class Level1 extends Scene { /* ... */ }
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class Level2 extends Scene { /* ... */ }
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class Level3 extends Scene { /* ... */ }
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// 玩家实体会自动在所有关卡间迁移
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Core.setScene(new PlayerSetupScene());
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// ... 游戏进行
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Core.loadScene(new Level1());
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// ... 关卡完成
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Core.loadScene(new Level2());
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// 玩家数据（血量、物品栏、属性）完整保留
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```
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### 2. 全局管理器
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```typescript
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class BootstrapScene extends Scene {
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protected initialize(): void {
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// 音频管理器 - 跨场景保持
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const audioManager = this.createEntity('AudioManager').setPersistent();
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audioManager.addComponent(new AudioController());
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// 成就管理器 - 跨场景保持
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const achievementManager = this.createEntity('AchievementManager').setPersistent();
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achievementManager.addComponent(new AchievementTracker());
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// 游戏设置 - 跨场景保持
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const settings = this.createEntity('GameSettings').setPersistent();
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settings.addComponent(new SettingsData());
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}
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}
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```
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### 3. 动态切换持久化状态
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```typescript
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class GameScene extends Scene {
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protected initialize(): void {
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// 初始创建为普通实体
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const companion = this.createEntity('Companion');
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companion.addComponent(new Transform(0, 0));
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companion.addComponent(new CompanionAI());
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// 监听招募事件
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this.eventSystem.on('companion:recruited', () => {
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// 招募后变为持久化实体
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companion.setPersistent();
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console.log('同伴已加入队伍，将跟随玩家跨场景');
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});
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// 监听解散事件
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this.eventSystem.on('companion:dismissed', () => {
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// 解散后恢复为场景本地实体
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companion.setSceneLocal();
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console.log('同伴已离队，不再跨场景');
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});
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}
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}
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```
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## 最佳实践
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### 1. 明确标识持久化实体
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```typescript
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// 推荐：在创建时立即标记
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const player = this.createEntity('Player').setPersistent();
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// 不推荐：创建后再标记（容易遗漏）
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const player = this.createEntity('Player');
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// ... 很多代码 ...
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player.setPersistent(); // 容易忘记
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```
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### 2. 合理使用持久化
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```typescript
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// ✓ 适合持久化的实体
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const player = this.createEntity('Player').setPersistent(); // 玩家
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const gameManager = this.createEntity('GameManager').setPersistent(); // 全局管理器
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const audioManager = this.createEntity('AudioManager').setPersistent(); // 音频系统
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// ✗ 不应持久化的实体
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const bullet = this.createEntity('Bullet'); // 临时对象
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const enemy = this.createEntity('Enemy'); // 关卡特定敌人
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const particle = this.createEntity('Particle'); // 特效粒子
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```
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### 3. 检查迁移后的实体
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```typescript
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class NewScene extends Scene {
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public onStart(): void {
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// 检查预期的持久化实体是否存在
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const player = this.findEntity('Player');
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if (!player) {
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console.error('玩家实体未正确迁移！');
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// 处理错误情况
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}
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}
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}
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```
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### 4. 避免循环引用
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```typescript
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// ✗ 避免：持久化实体引用场景本地实体
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class BadScene extends Scene {
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protected initialize(): void {
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const player = this.createEntity('Player').setPersistent();
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const enemy = this.createEntity('Enemy');
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// 危险：player 持久化但 enemy 不是
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// 场景切换后 enemy 被销毁，引用失效
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player.addComponent(new TargetComponent(enemy));
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}
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}
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// ✓ 推荐：使用 ID 引用或事件系统
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class GoodScene extends Scene {
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protected initialize(): void {
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const player = this.createEntity('Player').setPersistent();
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const enemy = this.createEntity('Enemy');
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// 存储 ID 而非直接引用
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player.addComponent(new TargetComponent(enemy.id));
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// 或使用事件系统通信
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}
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}
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```
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## 注意事项
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1. **已销毁的实体不会迁移**：如果实体在场景切换前被销毁，即使标记为持久化也不会迁移。
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2. **组件数据完整保留**：迁移时所有组件及其状态都会保留。
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3. **场景引用会更新**：迁移后实体的 `scene` 属性会指向新场景。
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4. **查询系统会更新**：迁移的实体会自动注册到新场景的查询系统中。
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5. **延迟切换同样生效**：使用 `Core.loadScene()` 延迟切换时，持久化实体同样会迁移。
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## 相关文档
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- [场景管理](./scene.md) - 了解场景的基本使用
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- [SceneManager](./scene-manager.md) - 了解场景切换
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- [WorldManager](./world-manager.md) - 了解多世界管理
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