Angular 2 ng for first，last，index loop [英] Angular 2 ngfor first, last, index loop

问题描述

在此示例中，我尝试将默认值设置为默认值: plunkr

I'm trying to set as default the first occurrence in this example: plunkr

出现以下错误:

Unhandled Promise rejection: Template parse errors:
TypeError: Cannot read property 'toUpperCase' of undefined ("dButtonToggleGroup">
                                                            <md-button-toggle [ERROR ->]*ngFor="let indicador of indicadores; #first = first" value="indicador.id" [checked]="first">
      "): ng:///AppModule/HomeComponent.html@35:78
Parser Error: Unexpected token #, expected identifier, keyword, or string at column 31 in [let indicador of indicadores; #first = first] in ng:///AppModule/HomeComponent.html@35:78 ("       <md-button-toggle *ngFor="let indicador of indicadores; #first = first" value="indicador.id" [ERROR ->][checked]="first">
                                                                <span>{{ indicado"): ng:///AppModule/HomeComponent.html@35:153

怎么了?

推荐答案

查看此 plunkr .

绑定变量时，需要使用方括号.另外，当您要获取对html中元素的引用时，可以使用井号标签，而不是在这样的模板内部声明变量.

When you're binding to variables, you need to use the brackets. Also, you use the hashtag when you want to get references to elements in your html, not for declaring variables inside of templates like that.

<md-button-toggle *ngFor="let indicador of indicadores; let first = first;" [value]="indicador.id" [checked]="first"> 
...

---

修改: 感谢 Christopher Moore : Angular公开了以下局部变量:

---

Thanks to Christopher Moore: Angular exposes the following local variables:

• index
• first
• last
• even
• odd

• index
• first
• last
• even
• odd

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