Angular 2 index in *ngFor

本文介绍如何在Angular中利用*ngFor指令遍历数组元素,并展示了如何使用索引进行遍历及如何结合函数控制元素显示的例子。

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Sometimes we need to iterate the array while developing with Angular 2, at that time, we may use *ngFor to iterate every elements in the array.


Introduction

First, codes below illustrate how to use *ngFor.
Suppose we have an array which names fruits and contains [“apple”, “pineapple”, “pear”]. Then we could use the following codes to iterate it.

<div class="father">
    <div class="children" *ngFor="#fruit of fruits">
        {{fruit}}
    </div>
</div>

It means that for each fruit in fruits, we append a div with class children . The final source code should be like this:

<div class="father">
    <div class="children" *ngFor="#fruit of fruits">
        apple
    </div>
    <div class="children" *ngFor="#fruit of fruits">
        pineapple
    </div>
    <div class="children" *ngFor="#fruit of fruits">
        pear
    </div>
</div>

Iterate with index

Since sometimes we need to indicate the number of element while iterating it. We could also add a variable that contains the index of iteration.
Take the same example above, we may construct the code like

<div class="father">
    <div class="children" *ngFor="#fruit of fruits; #i = index">
        No.{{(i + 1) + " " + fruit}}
    </div>
</div>

That will create a page like

<div class="father">
    <div class="children" *ngFor="#fruit of fruits">
        No.1 apple
    </div>
    <div class="children" *ngFor="#fruit of fruits">
        No.2 pineapple
    </div>
    <div class="children" *ngFor="#fruit of fruits">
        No.3 pear
    </div>
</div>

As you can see, we have already printed every element within the list using its index.


Index in function

Also we can use the index in a function, like

HTML file:

<div class="father">
    <div class="children" *ngFor="#fruit of fruits; #i = index" *ngIf="getExistance(i)">
        No.{{(i + 1) + " " + fruit}}
    </div>
</div>

Related TypeScript file:

...
getExistance(i: number){
    return i % 2 == 0;
}
...

We pass i as an argument to the function getExistance(). Then getExistance() determine if the element should appear.

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