在Angular 2中动态隐藏/显示工具提示

Question

I have some elements inside ngFor loop. Some of them have tooltips while others don't. When I use the following code like this:

<div ngFor="let item of items">
    <div [title]="item.title">

items that don't have tooltips will show undefined . Is there a way to hide it if the item doesn't have one while other items' tooltips still get to show?

Answer 1

Use the || operator to set the default value as an empty string if item.title is not defined. This will prevent the tooltip from being displayed. An example is shown in this stackblitz .

<div [title]="item.title || ''"> Some content </div>

Answer 2

I thought I would just add another couple approachs, in case you weren't aware, you can also do this:

<div [title]="getTitle()"> Some content </div>

Then in your typescript:

public getTitle(): string{
   return item.title || '';
}

---

Alternatively to this, you could take advantage of typescript getter/setters :

export class Item{
  private _title:string;
  get title():string {
      return this._title || '';
  }
  set title(value:string) {
      this._title = value;
  }
}

This way, title will never return null or undefined .