使用Knockout檢查「Select all」複選框onload

Question

我有一組Checkboxes和一個Select All複選框，使用Knockout按以下方式實現。我需要在頁面加載時默認選中「全選」複選框。

$(document).ready(function(){ 
    viewModel=new model(ko,$); 
    ko.applyBindings(viewModel); 
}); 

function model(ko,$){ 
    var jsonResponse= $.parseJSON(response); 

    this.factors=ko.observableArray(jsonResponse["factors"]); 
    this.selectedFactors=ko.observableArray(); 

    this.selectAll = ko.dependentObservable({ 
     read: function() { 
      return this.selectedFactors().length === this.factors().length; 
     }, 
     write: function(newValue) { 
      this.selectedFactors(this.selectedFactors().length === this.factors().length ? [] : this.factors().slice(0)); 
     }, 
     owner: this 
    }); 

}

HTML：

<table> 
    <tr> 
     <td><input type="checkbox" id="selectAll" data-bind="checked: selectAll" />Select All</td> 
    </tr> 
</table> 
<table data-bind="foreach: factorsSplitJsonArray"> 
    <tr data-bind="foreach: $data"> 
     <td> 
      <!-- ko if: $data.hasOwnProperty("factorCode") --> 
      <input type="checkbox" class="jqFactors" id="jqFactors" data-bind="checkedValue: $data, checked: $root.selectedFactors" /> 
      <span data-bind="text: factorDescription"></span> 
      <!-- /ko --> 
     </td> 
    </tr> 
</table> 

當我選擇或不選擇任何複選框或全選複選框selectedFactors得到改變的observableArray即。現在我需要在頁面加載時默認選擇「全選」複選框，而selectedFactors也應該包含所有選中的因素。

我是Knockout的新手，無法找到如何使用Knockout實現此功能。如果我們以某種方式顯式調用函數selectAll，它會完成這項工作嗎？我如何調用一個ko.dependentObservable函數。有人可以幫幫我嗎。

Answer 1

這裏有一個稍微不同的方法來得到同樣的事情：

var jsonData = { 
 
    allFactors: [ 
 
    { code: "A1", desc: "Alpha one" }, 
 
    { code: "A2", desc: "Alpha two" }, 
 
    { code: "B1", desc: "Beta one" }, 
 
    ], 
 
    
 
    // Simulate that no selection was ever made 
 
    selectedFactors: null // or "undefined" 
 
    
 
    // Unomment this version instead if you want to simulate loading 
 
    // data that was previously selected: 
 
    //selectedFactors: ["A1", "B1"] 
 
}; 
 

 
function ViewModel(data){ 
 
    var self = this; 
 
    
 
    self.factors = ko.observableArray(data.allFactors); 
 
    
 
    function getAllCodes() { 
 
    return data.allFactors.map(function(f) { return f.code; }); 
 
    } 
 
    
 
    self.selectedFactors = ko.observableArray(
 
    data.selectedFactors || getAllCodes() 
 
); 
 
    
 
    self.selectAll = ko.computed({ 
 
    read: function() { 
 
     return self.selectedFactors().length === self.factors().length; 
 
    }, 
 
    write: function(newVal) { 
 
     if (newVal === self.selectAll()) return;  
 
     if (!!newVal) self.selectedFactors(getAllCodes()); 
 
     if (!newVal) self.selectedFactors([]); 
 
    } 
 
    }); 
 
} 
 

 
ko.applyBindings(new ViewModel(jsonData));

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script> 
 

 
<label><input type="checkbox" data-bind="checked: selectAll"> Select All</label> 
 
<hr> 
 
<ul data-bind="foreach: factors"> 
 
    <li> 
 
    <label> 
 
     <input type="checkbox" data-bind="checkedValue: code, checked: $root.selectedFactors"> 
 
     <span data-bind="text: desc"></span> 
 
    </label> 
 
    </li> 
 
</ul>