Angular 4 嵌套 FormArrays 无法读取 属性 'push' of null

Question

我无法将推送到数组。 我有一个段（id，时间），可以有一个或几个人（角色，信息）。该字段是动态生成的。加载页面时显示字段（见下图）。

当尝试添加一个人时出现错误：ERROR TypeError: Cannot read property 'push' of null
这是 .ts 代码：

addPerson(index: number) {
//let personRows3 = <FormArray>this.mySummaryForm.get('personRows3'); 
let personRows3 = <FormArray>this.mySummaryForm.get(`segmentRows3.${index}.personRows3`)
personRows3.push(this.fb.group({
    personR3: '',
    personI3: ''
}));

}

  segmentRows3: this.fb.array([
    this.fb.group({
        segmentId3: '',
        segmentTime3: '',
        personRows3: this.fb.array([
        this.fb.group({
           personR3: '',
           personI3: ''
          })
        ])
    })
  ]),

.html代码

<div formArrayName="segmentRows3">
  <div *ngFor=" let segmentRow of mySummaryForm.controls.segmentRows3.controls; let i=index " > 
    <div  class="form-group" [formGroupName]="i" >   {{i+1}}
    <label for="segmentId3">Segment ID
        <select formControlName="segmentId3"  formControlName="segmentId3" placeholder="pick" type="text" id="segmentId3" class="form-control" [(ngModel)]="levelNumSegment3" (ngModelChange)="toNumberSegment3()">
            <option *ngFor="let level of segmentId" [value]="level.num">{{level.name}}</option>
        </select> 
    </label>      
    <label for="segmentTime3">Segment time
        <input formControlName="segmentTime3" type="text" id="segmentTime3" class="form-control" placeholder="select a time" (ngModelChange)="onChange($event)">
    </label>    
        <div formArrayName="personRows3">
            <div *ngFor=" let personRow of segmentRow.controls.personRows3.controls; let j=index " >
                <div  class="form-group" [formGroupName]="j" >   {{j+1}}    
                    <label for="personR3">person Role 
                    <input formControlName="personR3" [typeahead]="personRole" [typeaheadOptionsLimit]="10" [typeaheadMinLength]="0" type="text" id="personR3" class="form-control" placeholder="select a role" (ngModelChange)="onChange($event)" >
                    </label>
                    <label for="personI">Person infos
                    <input formControlName="personI3" [typeahead]="states" [typeaheadOptionsLimit]="10" [typeaheadMinLength]="0" type="text" id="personI3" class="form-control" placeholder="select infos" (ngModelChange)="onChange($event)" >
                    </label>
                    <label><span (click)="deletePerson(j)" class="btn btn-danger">Remove</span></label>
                </div> 
            </div>
        </div>
        <br><button type="button" (click)="addPerson(j)" class="btn btn-info">Add a person</button><br><br><br>
    </div> 
  </div>
</div>

Answer 1

当你的personRows3为null或没有元素时会出现上述错误

在推送元素之前添加检查，

if(personRows3){
  personRows3.push(this.fb.group({
    personR3: '',
    personI3: ''
  }));
}