ionic3 報錯： TypeError: XXX is not a function

貌似又是一個初級錯誤，問題出哪了？

報錯：Error: Uncaught (in promise): TypeError: _this.rest.getUserInfo is not a function

1.報錯截圖：

2.this.rest.getUserInfo 代碼行片斷：

3.公共 getUserInfo 方法：

======================================
loadUserPage方法源碼：

  public notLogin: boolean = true;
  public logined: boolean = false;
  headface: string;
  userinfo: string[];

  loadUserPage() {
    this.Storage.get('UserId').then((val) => {
      if (val != null) {
        //加載用戶數(shù)據(jù)
        var loading = super.showLoading(this.loadCtrl, "加載中..."); 
        this.rest.getUserInfo(val)
          .subscribe(
          userinfo => {
            this.userinfo = userinfo;
            this.headface = userinfo["UserHeadface"] + "?" + (new Date()).valueOf();
            this.notLogin = false;
            this.logined = true;
            loading.dismiss();
          }
          );
      }
      else {
        this.notLogin = true;
        this.logined = false;
      }
    });
  }