Nativescript中ViewModel方法绑定itemTap

Question

我对 Nativescript 事件处理有点困惑。我正在使用明确分离代码隐藏和视图模型的打字稿，并且我试图将 itemTap 属性绑定到视图模型方法（就像在https://github.com/NativeScript/template-hello-world 中显示的示例中一样-ts/blob/master/main-view-model.ts）。

XML：

<Page xmlns="http://schemas.nativescript.org/tns.xsd" navigatingTo="navigatingTo" loaded="pageLoaded" class="page">
  <StackLayout>
    <ListView items="{{ items }}" itemTap="onItemTapped">
      <ListView.itemTemplate>
        <Label text="{{ Name }}"/>
      </ListView.itemTemplate>
    </ListView>
  </StackLayout>
</Page>

代码隐藏：

import { EventData } from 'data/observable';
import { Page } from 'ui/page';
import { EditItemViewModel } from '../../ViewModels/EditItemViewModel';

export function navigatingTo(args: EventData) {
    let page = <Page>args.object;
    page.bindingContext = new EditItemViewModel();
}

视图模型：

import { Observable } from 'data/observable';
import { ObjectRelationalMapper } from '../Common/Data'
import { WebServiceDataManager } from '../Common/Data'

import { Item } from '../Models/Item';

export class EditItemViewModel extends Observable {
  _wsDataManager: WebServiceDataManager;
  _orm: ObjectRelationalMapper;
  _items: Array<Item>;

  get items(): Array<Item> {
    return this._items;
  }

  set items(items: Array<Item>) {
    this._items = items;
  }

  constructor() {
    super();
    this._wsDataManager = new WebServiceDataManager();
    this._orm = new ObjectRelationalMapper();
    this.listAllItems();
  }

  private listAllItems(): void {
    this._orm.getAllObjects(Item, this, this.onItemsReceived)
  }

  public onItemsReceived(items: Array<Item>) {
    this._items = items;
    this.notify({ object: this, eventName: Observable.propertyChangeEvent, propertyName: 'items', value: this._items });
  }

  public onItemTapped(args): void {
    let tappedView: any = args.view;
    let tappedItem: Item = tappedView.bindingContext;
  }
}

该onItemTapped方法不会被解雇。如果我onItemTapped输入代码隐藏：

export function onItemTapped(args): void {
    let tappedView: any = args.view;
    let tappedItem: any = tappedView.bindingContext;
}

..它按预期工作。在 viewModel 中使用事件处理程序有什么问题，为什么“HelloWorld”示例如此具有误导性？

Answer 1

问题是，在第一种情况下，您的onItemTapped来自您的视图模型。因此，您应该像引用视图模型属性items和name一样引用它，这意味着使用双大括号：

<ListView items="{{ items }}" itemTap="{{ onItemTapped }}">

现在，如果onItemTapped函数放置在您的代码隐藏文件中，那么您可以直接引用它，如您的代码中所写：

<ListView items="{{ items }}" itemTap="onItemTapped">