KnockoutJS:从 JavaScript 模板中访问数组中项目的索引 [英] KnockoutJS: Access index of item in array from within the JavaScript template

问题描述

我使用 KnockoutJS 从数组中填充列表:

<input type="text" data-bind="value: myText"/>
函数视图模型(){self.list = ko.observableArray([新列表项(示例文本")]);};功能列表项(文本){this.myText = 文本；};

我可以像这样为我的输入的各个实例分配一个 id

<input data-bind="attr: { id: $index } ...

如何从我的 listItem 函数中访问该索引?我希望能够做类似的事情

function listItem (text) {this.myText = 文本；this.index = $index;};

为了将其用于进一步处理.

解决方案

您可以创建一个自定义绑定，将您的属性设置为索引，它看起来像:

ko.bindingHandlers.setIndex = {初始化:函数(元素，valueAccessor，allBindings，数据，上下文){var prop = valueAccessor();数据[prop] = context.$index;}};

这假设您正在处理数组中的对象.你会像这样使用它:

<li data-bind="setIndex: 'myIndex', text: name"></li>

因此，这会将 $index observable 复制到具有您指定的属性名称的对象上.示例:http://jsfiddle.net/rniemeyer/zGmcg/

在绑定之外执行此操作的另一种方法(这是我在 $index 之前使用的方法)是订阅对 observableArray 的更改并每次重新填充索引.

observableArray 的扩展如下所示:

//跟踪 observableArray 中项目的索引ko.observableArray.fn.indexed = 函数(道具){道具 = 道具 ||'指数';//每当数组更改时，进行一个循环以更新每个数组的索引this.subscribe(function(newValue) {如果(新值){变量项目；for (var i = 0, j = newValue.length; i < j; i++) {item = newValue[i];如果 (!ko.isObservable(item[prop])) {item[prop] = ko.observable();}项目[道具](i);}}});//初始化索引this.valueHasMutated();返回这个；};

然后你会像这样使用它:

this.myItems = ko.observableArray().indexed('myIndexProp');

这是一个示例:http://jsfiddle.net/rniemeyer/bQD2C/

I populate a list from an array using KnockoutJS:

<div data-bind:"foreach: list">
   <input type="text" data-bind="value: myText" />
</div>

function ViewModel() {
    self.list = ko.observableArray([
        new listItem("sample text")
    ]);
};

function listItem (text) {
    this.myText = text;
};

I can assign an id to the individual instances of my input like so

<input data-bind="attr: { id: $index } ...

How do I access this index from within my listItem function? I want to be able to do something like

function listItem (text) {
    this.myText = text;
    this.index = $index;
};

in order to use this for further processing.

解决方案

You could create a custom binding that sets your property to the index, it would look something like:

ko.bindingHandlers.setIndex = {
    init: function(element, valueAccessor, allBindings, data, context) {
        var prop = valueAccessor();
        data[prop] = context.$index;
    }        
};

This assumes that you are dealing with objects in your array. You would use it like:

<ul data-bind="foreach: items">
    <li data-bind="setIndex: 'myIndex', text: name"></li>
</ul>

So, this copies the $index observable on to your object with the property name that you specify. Sample: http://jsfiddle.net/rniemeyer/zGmcg/

Another way that you can do this outside of bindings (this is how I used to do it before $index) is to subscribe to changes to the observableArray and repopulate an index each time.

Here is what an extension to an observableArray might look like:

//track an index on items in an observableArray
ko.observableArray.fn.indexed = function(prop) {
    prop = prop || 'index';
   //whenever the array changes, make one loop to update the index on each
   this.subscribe(function(newValue) {
       if (newValue) {
           var item;
           for (var i = 0, j = newValue.length; i < j; i++) {
               item = newValue[i];
               if (!ko.isObservable(item[prop])) {
                  item[prop] = ko.observable();
               }
               item[prop](i);      
           }
       }   
   }); 

   //initialize the index
   this.valueHasMutated(); 
   return this;
};

You would then use it like:

this.myItems = ko.observableArray().indexed('myIndexProp');

Here is a sample: http://jsfiddle.net/rniemeyer/bQD2C/

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