Angular 前端下拉选择框

html：

<nz-form-item>
            <nz-form-label [nzSm]="6" [nzXs]="24" nzRequired nzFor="gradeNo">年级</nz-form-label>
            <nz-form-control [nzSm]="14" [nzXs]="24">
              <nz-select (click)="searchGradeList()" [(ngModel)]="grade" formControlName="gradeNo" id="gradeNo" [nzSize]="size"
                nzPlaceHolder="请选择年级" nzShowSearch>
                <nz-option *ngFor="let option of gradeListOfOption" [nzLabel]="option.name" [nzValue]="option.code"></nz-option>
              </nz-select>
            </nz-form-control>
</nz-form-item>

ts：

searchGradeList() {
    this.gradeListOfOption = [{ name: '大一', code: '1' },
    { name: '大二', code: '2' },