Angular：嵌套表单“无法读取null的属性'长度'”

Question

我有一个嵌套表单，这里是formcontrols：

this.newRequest = this._fb.group({
    requestType: [],
    tripType: [],
    feeders: [''],
    directFlight: [],
    departure: [''],
    arrival: [''],
    depDate: [''],
    arrDate: [''],
    nbPax: ['', [Validators.max(95), Validators.min(1), Validators.pattern('^[0-9]+$')]],
    class: [''],
    daterangeToggle: [],
    viaToggle: [],
    detailsToggle: [],
    roundway: this._fb.array([
        this.initRoundway()
    ])
});  

initRoundway() {
    return this._fb.group({
        daterangeOutFrom: [],
        daterangeOutTo: [],
        viaOut: this._fb.array([]),
        viaIn: this._fb.array([]),
        flights: this._fb.array([
            this.initFlights()
        ])
    });
}

initFlights() {
    return this._fb.group({
        class: ['', Validators.required],
        flightNb: [''],
        timeMin: [''],
        timeMax : ['']
    });
}

我在访问viaOut和flightNb时遇到问题。

我试过了：

const control1 = <FormArray>this.newRequest.controls['roundway'];
if (control1.controls['viaOut'].length===0) {...}

还有：

const control1 = <FormArray>this.newRequest.get('roundway.viaOut');
if (control1.length === 0) {...}

但两者都不起作用，我收到错误"Cannot read property 'length' of null"

修改

这是使用第一个代码的console.log（control1）的输出。

感谢。

Answer 1

嗨，请试试这个，

const control1 = <FormArray>this.newRequest.controls['roundway'];
if (control1.controls['viaOut']['controls'].length===0) {...}

OR

const control1 = <FormArray>this.newRequest.get('roundway.0.viaOut');
if (control1.length === 0) {...}