如何使用 *NgIf 或任何 Ng 函數刪除 Dom 元素和組件？我有一個下拉列表；根據下拉菜單，它將顯示不同的形式。當人員更改下拉類型然后稍后返回相同的下拉類型時 - 以前的表單數據仍然存在，何時應該清除。當下拉列表更改時刪除所有表單、變量和組件本身的最佳方法是什么？見下面的聲明，<div class = "addressformtotal">    <div class = "addressblock">        <app-address-formatheader-form></app-address-formatheader-form>        <div *ngIf="formatMessage?.addressFormatDescription.includes('Standard')"><app-address-mailing-standard-form></app-address-mailing-standard-form></div>        <div *ngIf="formatMessage?.addressFormatDescription.includes('Military')"><app-address-mailing-military-form></app-address-mailing-military-form></div>        <div *ngIf="formatMessage?.addressFormatDescription.includes('Post')"><app-address-mailing-pobox-form></app-address-mailing-pobox-form></div>        <div *ngIf="formatMessage?.addressFormatDescription.includes('Free')"><app-address-free-form></app-address-free-form></div>        <div *ngIf="formatMessage?.addressFormatDescription.includes('Rural')"><app-address-mailing-rural-form></app-address-mailing-rural-form></div>        <div *ngIf="formatMessage?.addressFormatDescription.includes('International')"><app-address-mailing-international-form></app-address-mailing-international-form></div>    </div>