Angular 2 - ngFor - 局部变量“first"不起作用 [英] Angular 2 - ngFor - local variable "first" does not work

问题描述

我正在使用 ngFor 循环来创建一个带有按钮的列表来移动对象.我试图首先和最后使用 ngFor 变量来禁用某些按钮.我发现第一"不起作用

I am using ngFor loop to create a list with buttons to move objects around. I have attempted to use the ngFor variables first and last to disable certain buttons. I am finding "first" does not work

<ul>
<li *ngFor="#hero of heroes; #i=index, #first=first, #last=last">
    <button class="btn btn-default btn-lg" [disabled]="first" (click)="moveToTop(hero, i)">Top</button>
    <button class="btn btn-default btn-lg" [disabled]="first" (click)="moveUp(hero, i)">Up</button>
    <button class="btn btn-default btn-lg" [disabled]="last" (click)="moveDown(hero, i)">Down</button>
    <button class="btn btn-default btn-lg" [disabled]="last" (click)="moveToBottom(hero, i)">Bottom</button>
</li>

我在这里有一个工作示例 Plunker 预览

I have a working example here Plunker preview

我这样做正确吗?我知道我可以做到

Am I doing this correctly? I know I could do

[disabled]="i==0"

但我认为第一个"和最后一个"看起来更优雅.

but I was thinking "first" and "last" looked more elegant.

推荐答案

现在你可以使用 [disabled]="i === 0" 因为局部变量 first 不存在，但有一个 pull request 来添加它，尚未合并尽管.

For now you can use [disabled]="i === 0" since the local variable first doesn't exist, but there's a pull request to add it, not yet mergerd though.

更新

上面的pull request引用在beta.15登陆，可以看到changelog https://github.com/angular/angular/blob/master/CHANGELOG.md.

The pull request reference above it landed with beta.15, you can see the changelog https://github.com/angular/angular/blob/master/CHANGELOG.md.

这是一个 plnkr，first 正在运行.您也可以查看文档.

Here's a plnkr with first working. You can see the documentation as well.

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