我在Angular4的订阅中得到的数据为空

Question

我带着怀疑得到了数据，显示了这些数据，然后调用了函数，但是函数说“ null”。对不起我的英语不好。谢谢。

 this.service.prepareNewVersion().subscribe(data2 => {
       console.log("data2 ", data2);
       this.service.myBlockPeriod = data2;
       console.log(" prepareNewVersion ",   this.service.myBlockPeriod);
  });
 console.log(" before ",   this.service.myBlockPeriod);
 this.showYearsExec();


private showYearsExec() {
        console.log("showYearsExec", this.service.myBlockPeriod);
        let list: Array<string> = this.service.myBlockPeriod;

    if (list !== null) {

        list.forEach(element => {
            this.arrayYears.push(element.substring(0, 4));
        });



        // Se eliminan los años repetidos.
        let unique = this.arrayYears.filter(function (elem, index, self) {
            return index === self.indexOf(elem);
        })

        // Combo de años de la vista.
        this.arrayYears = unique;

        // Se añaden al servicio
        this.service.yearsInExec = unique;
    }

}

Answer 1

您的代码是异步执行的，到执行“ this.showYearsExec（）”时，尚未解决“ prepareNewVersion（）”方法的承诺，因此结果为空。

执行“ this.showYearsExec（）;”在这样的订阅方法中：

this.service.prepareNewVersion().subscribe(data2 => {
       console.log("data2 ", data2);
       this.service.myBlockPeriod = data2;
       console.log(" prepareNewVersion ",   this.service.myBlockPeriod);
       console.log(" before ",   this.service.myBlockPeriod);
       this.showYearsExec();
  });