Einführung in die Implementierungsmethode umfangreicher interaktiver Rückgängig- und Vorwärtsoperationen in Webanwendungen (Code)

import { Inject } from "@angular/core";
import { IndexedDBAngular } from "indexeddb-angular";
import { Subject, Observer, Observable } from "rxjs";

export interface IDBData {
    widgetList: string
}

// 前进和后退的服务
@Inject({
    providedIn: 'root'
})
export class PanelExtendMoveBackService {

    /**
     * 发射DB集合存储的数据，可订阅
     */
    public launchDBDataValue$: Subject<idbdata> = new Subject<idbdata>()

    /**
     * 创建一个叫panelDataDB的本地数据库，版本号为1
     */
    public db = new IndexedDBAngular('panelDataDB', 1)

    /**
     * 记录前进和后退的存储集合项的下标key
     * 默认为0
     */
    public dbCurrentIndex: number = 0

    /**
     * 自增的DBkey
     */
    public dbKey: number = -1

    // 是否允许前进
    public get isMove() : boolean {
        return this.dbCurrentIndex  0
    }

    constructor() {}

    /**
     * 创建DB集合
     */
    public createCollections(): Observable<boolean> {
        const _sub: Subject<boolean> = new Subject<boolean>()
        this.dbKey = -1
        this.db.createStore(1, (db: any) => {
            db.currentTarget.result.createObjectStore('panelItem')
        }).then(()=>{
            this.dbClear()
            _sub.next(true)
        })
        return _sub.asObservable()
    }

    /**
     * 往集合里添加数据
     * 同时把新添加的key赋值给dbCurrentIndex，
     */
    public dbAdd(): void {
        this.handleDbCurrentRefreshDB();
        this.dbKey += 1;
        // 此处存储你要保存的数据
        const _widget_list = []
        this.db.add('panelItem', { widgetList: JSON.stringify(_widget_list) }, this.dbKey).then(
            _e => {
                if ((<object>_e).hasOwnProperty('key')) {
                    this.dbCurrentIndex = _e.key
                };
            },
            () => {
                this.dbKey -= 1
                throw new Error('添加panelItem集合失败')
            }
        )
    }

    /**
     * 在执行添加数据集操作的时候判断dbCurrentIndex当前指引的下标是否低于dbKey
     * 如果是说明执行了后退操作之后后续动作执行了dbAdd的操作，则清空dbCurrentIndex索引之后的数据重新添加
     */
    public handleDbCurrentRefreshDB(): void {
        if (this.dbCurrentIndex  {})
            }
            this.dbKey = this.dbCurrentIndex
        }
    }

    /**
     * 执行后退操作发射DB数据集
     */
    public acquireBackDBData(): void {
        if( this.isBack ) {
            this.dbCurrentIndex -= 1
            this.db.getByKey('panelItem', this.dbCurrentIndex).then(res=>{
                this.launchDBDataValue$.next(res)
            },()=>{ })
        }
    }

    /**
     * 执行前进操作发射DB数据集
     */
    public acquireMoveDBData(): void {
        if( this.isMove ) {
            this.dbCurrentIndex += 1
            this.db.getByKey('panelItem', this.dbCurrentIndex).then(res => {
                this.launchDBDataValue$.next(res)
            }, () => { })
        }
    }

    /**
     * 清除DB集合panelItem
     */
    public dbClear(): void {
        this.db.clear('panelItem').then(_e => {})
    }
}</object></boolean></boolean></boolean></idbdata></idbdata>