IONIC 4 + Angular7: ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'then' of undefined

Question

我想将创建 SQLite 数据库的结果分配给 SQLiteObject 类型的变量数据库，因此我必须在 "then" 块中执行此操作，但它显示

error ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'then' of undefined.

关于这个错误的大部分文章我都试过了"ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'then' of undefined" 但是 none 个是我的答案

constructor(public http: Http,
    private sqlitePorter: SQLitePorter,
    private storage: Storage,
    private sqlite: SQLite,
    private plateform: Platform) {
    this.databaseReady = new BehaviorSubject(false);
    this.plateform.ready().then(() => {
      this.sqlite.create({
        name: 'developers.db',
        location: 'default',
        })
        .then((db: SQLiteObject) => {
        this.database = db;
        this.storage.get('database_filled').then(val => {
          if (val) {
            this.databaseReady.next(true);
          } else {
            this.fillDatabase();
          }
        })
      })
    })
  }

Answer 1

您必须 return 从第一个 then 开始的承诺。由于您没有 return 从第一个 then 开始，它将 return undefined。尝试这样的事情。

this.plateform.ready().then(() => {
      return this.sqlite.create({
        name: 'developers.db',
        location: 'default',
        })
        .then((db: SQLiteObject) => {
        this.database = db;
        this.storage.get('database_filled').then(val => {
          if (val) {
            this.databaseReady.next(true);
          } else {
            this.fillDatabase();
          }
        })
      })
    })

IONIC 4 + Angular7: ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'then' of undefined

IONIC 4 + Angular7: ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'then' of undefined

observable

typescript

angular

ionic4

rxjs6