为什么Dropdown值不会使用Angular？

<select #classProductTypeCombobox 
        name="classProductTypeCombobox" 
        class="form-control col-md-3" 
        [(ngModel)]="classification.codeType"
        [attr.data-live-search]="true" 
        jq-plugin="selectpicker" 
        required>
    <option *ngFor="let classType of classificationTypes" 
            [value]="classType">{{classType}}</option>
</select>

角度代码：

getClassificationTypes(): void {
    //need to remove hard coding
    this._commonService.getLookupItems(1,6).subscribe((result) => {
        this.classificationTypes= result.items;

    });
}

ngOnInit(): void {
    this.getClassificationTypes();
}

当我尝试调试代码时,classificationTypes有适当的数据,我用作硬编码值的数据.它工作正常.

方法getClassificationTypes调用API从数据库中获取数据.

我正在使用ASP.NET Zero框架编写此应用程序.

我尝试了以下解决方案.这是将数据绑定到下拉列表,但是下拉列表的自动搜索功能已经消失,它显示简单的下拉列表.并在控制台中,它提供以下错误消息.

getClassificationTypes(): any {
    return this._commonService.getLookupItems(2,6).subscribe((result) => {
        console.log(result.items)
        return this.classificationTypes = result.items;
    });
}

classificationTypes: TaxonomyItemsLocDto[] = this.getClassificationTypes();


ERROR Error: Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays

在控制台日志中,classificationTypes显示为[classType,classType,classType]

来自API的回复：

{"result":{"items":[{"taxonomyItemsId":4,"taxonomyMasterId":2,"taxonomyItemLocDesc":"Sales"},{"taxonomyItemsId":5,"taxonomyItemLocDesc":"Administrative"},{"taxonomyItemsId":6,"taxonomyItemLocDesc":"Financial"},{"taxonomyItemsId":7,"taxonomyItemLocDesc":"Informative"}]},"targetUrl":null,"success":true,"error":null,"unAuthorizedRequest":false,"__abp":true}