Angular 4.x EventManager & Custom EventManagerPlugin

時間 2019-11-06

標籤 angular 4.x eventmanager custom eventmanagerplugin 欄目 AngularJS 简体版

原文原文鏈接

在 Angular 中如何爲同一個表達式綁定多個事件呢？若是咱們這樣作可能會是這樣的：html

<div>
   <button (click, mouseover)="onClick()">Click me</button>
</div>

在繼續分析綁定多個事件以前，咱們先來分析一下，若是在模板中綁定一個事件如 click 事件，Angular 是如何工做的？typescript

<div>
   <button (click)="onClick()">Click me</button>
</div>

Angular 在解析 DOM 樹的時候，對於事件綁定它會調用 DomRenderer 實例的 listen() 方法，進行事件綁定，listen() 方法具體實現以下：bootstrap

// angular2/packages/platform-browser/src/dom/dom_renderer.ts
class DefaultDomRenderer2 implements Renderer2 {
    ....
    listen(target: 'window'|'document'|'body'|any, event: string, 
      callback: (event: any) => boolean):
          () => void {
        checkNoSyntheticProp(event, 'listener');
        if (typeof target === 'string') {
          return <() => void>this.eventManager.addGlobalEventListener(
              target, event, decoratePreventDefault(callback));
        }
        return <() => void>this.eventManager.addEventListener(
                   target, event, decoratePreventDefault(callback)) as() => void;
    }
}

經過源碼咱們發現，無論走哪條分支，最終都是調用 this.eventManager 對象的方法設置事件監聽。這裏的 this.eventManager 是什麼？它是 Angular 中的事件管理器 EventManager，咱們先來會會它。數組

EventManager (事件管理器)

在 Angular 中全部的事件綁定都是由一個事件管理器來驅動，事件管理器自己由多個事件插件提供支持。Angular 中內置的事件插件以下：緩存

KeyEventsPlugin - 處理鍵盤事件angular2
HammerGesturesPlugin - 處理手勢app
DomEventsPlugin - 處理 DOM 事件dom

看完上面的內容，相信不少人也會有疑問 - EventManager 究竟是如何管理不一樣事件的呢？要揭開這背後的祕密，咱們的惟一途徑就是看源碼，由於它是最誠實的，它對你毫無保留，此刻腦海中忽然想起一首歌：ide

美麗的神話函數

解開我最神祕的等待
星星墜落風在吹動
終於再將你擁入懷中
….

愛是心中惟一不變美麗的神話

放鬆一下，立刻回到正題 - EventManager 類：

EventManager 類

// angular2/packages/platform-browser/src/dom/events/event_manager.ts
export class EventManager {
  // EventManagerPlugin列表
  private _plugins: EventManagerPlugin[]; 
  // 緩存已匹配的eventName與對應的插件
  private _eventNameToPlugin = new Map<string, EventManagerPlugin>();

  constructor(
    @Inject(EVENT_MANAGER_PLUGINS) plugins: EventManagerPlugin[], 
    private _zone: NgZone) {
        plugins.forEach(p => p.manager = this);
        /**
         * {provide: EVENT_MANAGER_PLUGINS, useClass: DomEventsPlugin, multi: true},
         * {provide: EVENT_MANAGER_PLUGINS, useClass: KeyEventsPlugin, multi: true},
         * {provide: EVENT_MANAGER_PLUGINS, useClass: HammerGesturesPlugin, multi: true}
         * 
         * slice(): 建立新的plugins數組
         * reverse(): 讓DomEventsPlugin插件做爲列表最後一項，由於它可以處理全部的事件。
        */
        this._plugins = plugins.slice().reverse();
  }

  // 獲取能處理eventName的插件，並調用對應插件提供的addEventListener()方法
  addEventListener(element: HTMLElement, eventName: string,
    handler: Function): Function {
        const plugin = this._findPluginFor(eventName);
        return plugin.addEventListener(element, eventName, handler);
  }

  // 獲取能處理eventName的插件，並調用對應插件提供的addGlobalEventListener()方法
  addGlobalEventListener(target: string, eventName: string, 
    handler: Function): Function {
        const plugin = this._findPluginFor(eventName);
        return plugin.addGlobalEventListener(target, eventName, handler);
  }

  // 獲取NgZone
  getZone(): NgZone { return this._zone; }

  /** @internal */
  _findPluginFor(eventName: string): EventManagerPlugin {
    // 優先從_eventNameToPlugin對象中獲取eventName對應的EventManagerPlugin
    const plugin = this._eventNameToPlugin.get(eventName);  
    if (plugin) {
      return plugin;
    }

    // 遍歷插件列表，判斷當前插件是否支持eventName對應的事件名
    const plugins = this._plugins;
    for (let i = 0; i < plugins.length; i++) {
      const plugin = plugins[i];
      if (plugin.supports(eventName)) {
        this._eventNameToPlugin.set(eventName, plugin);
        return plugin;
      }
    }
    throw new Error(`No event manager plugin found for event ${eventName}`);
  }
}

EventManagerPlugin 抽象類

export abstract class EventManagerPlugin {
  constructor(private _doc: any) {}

  manager: EventManager;

  // 判斷是否支持eventName對應的事件
  abstract supports(eventName: string): boolean;

  // 添加事件監聽
  abstract addEventListener(element: HTMLElement, eventName: string, 
    handler: Function): Function;

  // 添加全局的事件監聽
  addGlobalEventListener(element: string, eventName: string, 
    handler: Function): Function {
      const target: HTMLElement = getDOM().getGlobalEventTarget(this._doc, element);
       if (!target) {
           throw new Error(`Unsupported event target ${target} for event 
            ${eventName}`);
       }
       return this.addEventListener(target, eventName, handler);
  };
}

時機已成熟，接下來咱們開始實現上述的功能。

自定義插件

Step 1: Creating a new plugin

正如上面提到的，咱們但願在咱們的 Angular 模板上有多個事件綁定到同一個表達式：

<div>
   <button (click, mouseover)="onClick()">Click me</button>
</div>

若是是這樣，咱們的 supports() 函數的內部規則應該很清楚。咱們須要一個字符串，其中有一個或多個逗號，分隔事件名稱。當人們把一些愚蠢的東西放在(,click)中時，咱們也應該處理。因此咱們的 supports() 函數以下：

getMultiEventArray(eventName: string): string[] {
  return eventName.split(",")
    .filter((item, index): boolean => { return item && item != '' })
}

supports(eventName: string): boolean {
  return this.getMultiEventArray(eventName).length > 1
}

這將容許 EventManager 將事件字符串如 (click, mouseover) 委派給此插件。

Step 2: Implementing the eventListeners

如今咱們已經實現了supports() 方法，EventManager 將調用 plugin.addEventListener() 方法，所以插件須要實現 addEventListener() 方法，從而實現咱們的自定義行爲。咱們的自定義行爲很簡單 - 爲咱們解析的eventArray 中的全部事件添加事件偵聽器。

addEventListener

addEventListener(element: HTMLElement, eventName: string, handler: Function): Function {
        let zone = this.manager.getZone();
        let eventsArray = this.getMultiEventArray(eventName);

        // Entering back into angular to trigger changeDetection
        let outsideHandler = (event: any) => {
            zone.runGuarded(() => handler(event));
        };

        // Executed outside of angular so that change detection is not 
        // constantly triggered.
        let addAndRemoveHostListenersForOutsideEvents = () => {
            eventsArray.forEach((singleEventName: string) => {
                this.manager.addEventListener(element, singleEventName, outsideHandler);
            });
        }

        return this.manager.getZone()
                   .runOutsideAngular(addAndRemoveHostListenersForOutsideEvents);
    }

addGlobalEventListener

addGlobalEventListener(target: string, eventName: string, handler: Function): Function {
        let zone = this.manager.getZone();
        let eventsArray = this.getMultiEventArray(eventName);
        let outsideHandler = (event: any) => zone.runGuarded(() => handler(event));

        return this.manager.getZone().runOutsideAngular(() => {
            eventsArray.forEach((singleEventName: string) => {
                this.manager.addGlobalEventListener(target, singleEventName, 
                    outsideHandler);
            })
        });
}

Step 3: Register plugin

import { EVENT_MANAGER_PLUGINS } from '@angular/platform-browser';

@NgModule({
  ...
  providers: [
    { provide: EVENT_MANAGER_PLUGINS, useClass: MultiEventPlugin, multi: true }
  ]
})
export class AppModule { }

完整示例

multi-event.plugin.ts

import { Injectable, Inject } from '@angular/core';
import { EventManager, DOCUMENT, ɵd as EventManagerPlugin } from '@angular/platform-browser';

/**
 * Support Multi Event
 */
@Injectable()
export class MultiEventPlugin extends EventManagerPlugin {
    manager: EventManager;

    constructor( @Inject(DOCUMENT) doc: any) { super(doc); }

    getMultiEventArray(eventName: string): string[] { 
        return eventName.split(",")   // click,mouseover => [click,mouseover]
            .filter((item, index): boolean => { return item && item != '' })
    }

    supports(eventName: string): boolean {
        return this.getMultiEventArray(eventName).length > 1;
    }

    addEventListener(element: HTMLElement, eventName: string, 
      handler: Function): Function {
        let zone = this.manager.getZone();
        let eventsArray = this.getMultiEventArray(eventName);

        // Entering back into angular to trigger changeDetection
        let outsideHandler = (event: any) => {
            zone.runGuarded(() => handler(event));
        };

        // Executed outside of angular so that change detection is
        // not constantly triggered.
        let addAndRemoveHostListenersForOutsideEvents = () => {
            eventsArray.forEach((singleEventName: string) => {
                this.manager.addEventListener(element, singleEventName, outsideHandler);
            });
        }

        return this.manager.getZone()
                .runOutsideAngular(addAndRemoveHostListenersForOutsideEvents);
    }

    addGlobalEventListener(target: string, eventName: string, 
      handler: Function): Function {
        let zone = this.manager.getZone();
        let eventsArray = this.getMultiEventArray(eventName);
        let outsideHandler = (event: any) => zone.runGuarded(() => handler(event));

        return this.manager.getZone().runOutsideAngular(() => {
            eventsArray.forEach((singleEventName: string) => {
                this.manager.addGlobalEventListener(target, singleEventName, 
                    outsideHandler);
            });
        });
    }
}

app.component.ts

import { Component } from '@angular/core';

@Component({
  selector: 'exe-app',
  template: `
    <div>
      <button (click,mouseover)="onClick()">Click me</button>
    </div>
  `
})
export class AppComponent {
  onClick() {
    console.log('Click');
  }
}

app.module.ts

import { NgModule, CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';
import { EVENT_MANAGER_PLUGINS } from '@angular/platform-browser';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';

import { AppComponent } from './app.component';
import { MultiEventPlugin } from './plugins/multi-event.plugin';

@NgModule({
  imports: [BrowserModule],
  declarations: [AppComponent],
  bootstrap: [AppComponent],
  providers: [
    { provide: EVENT_MANAGER_PLUGINS, useClass: MultiEventPlugin, multi: true }
  ],
  schemas: [CUSTOM_ELEMENTS_SCHEMA]
})
export class AppModule { }