如何提高ngFor循环的性能？

Question

当ngFor应该呈现7600个字符串项时,性能非常慢,浏览器会冻结几秒钟.

是否有可能提高ngFor的性能？

ng代码:

  <ul *ngIf="isOpen"
    class="nano-drop-down-list"
    dropdownMenu>
    <li class="nano-f-r nano-f-30">
        <input [(ngModel)]="searchString"
               class="nano-f nano-p-0_10 nano-bc-ws hover-effect"
               placeholder="Search..." type="text"/>
    </li>

    <!-- ngFor which should be improved -->
    <li *ngFor="let option of arrayOfOptions | nanoSearchByKey:searchString:displayProperty;"
        [ngClass]="{'active':isOptionSelected(option[valueProperty])}"
        class="nano-f-r nano-f-30 nano-bc-ws hover-effect">
        <button (click)="handleClickOnOption(option[valueProperty]);"
                type="button"
                class="nano-f-c nano-f nano-p-0_10 nano-overflow-h">
            <div class="nano-f-r nano-f">
                <span class="nano-m-aaa0 nano-overflow-e">
                    {{ option[displayProperty] }}
                </span>
                <div *ngIf="isMultiple"
                     class="nano-f-r nano-f-30">
                    <i *ngIf="isOptionSelected(option[valueProperty])"
                       class="fa fa-check nano-m-a"
                       aria-hidden="true"></i>
                </div>
            </div>
        </button>
    </li>
</ul>

Answer 1

NgForOf在Angular 6中提供了覆盖track by函数(源)的选项.它允许您选择角度应检查更改的属性/条件.

为此,只需向组件添加一个方法,如下所示:

trackByFn(index, item) {
  return item.someUniqueIdentifier;
  // or if you have no unique identifier:
  // return index;
}

而在您的组件HTML中,您将循环更改为

<li *ngFor="let option of arrayOfOptions | nanoSearchByKey:searchString:displayProperty; trackBy: trackByFn"
        [ngClass]="{'active':isOptionSelected(option[valueProperty])}"
        class="nano-f-r nano-f-30 nano-bc-ws hover-effect">

Angular会自动将当前索引以及当前项传递给函数.

这是一个很好的帖子,有更具体的例子和更多信息(感谢@Pedro Arantes).