javascript - 为什么 ObservableArray 对象的访问在子 foreach 中不起作用?
问题描述
您好,我是淘汰赛的新手,我遇到了这样一种情况,即我正在创建一个带有嵌套 foreach 的表,但内循环在与外循环匹配的条件下工作,但是当上面的对象是给定的普通数组时它正在工作。
viewModel.Subject=ko.observableArray(['Science','Math']);
下面给定的 observable 无法绑定子元素
viewModel.SubjectClass=ko.observableArray([{'Class':'8','Subject':'Science'},{'Class':'7','Subject':'Math'},{'Class':'8','Subject':'Science'},{'Class':'6','Subject':'Math'}]);
var viewModel={};
viewModel.Subject=ko.observableArray(['Science','Math']);
viewModel.SubjectClass=ko.observableArray([{'Class':'8','Subject':'Science'},{'Class':'7','Subject':'Math'},{'Class':'8','Subject':'Science'},{'Class':'6','Subject':'Math'}]);
viewModel.Students=ko.observableArray([
{'StId':1,'StName':'John','Class':'8','Subject':'Science'},
{'StId':2,'StName':'Martha','Class':'7','Subject':'Math'},
{'StId':3,'StName':'George','Class':'6','Subject':'Math'},
{'StId':4,'StName':'Martin','Class':'8','Subject':'Science'},
{'StId':5,'StName':'Donny','Class':'7','Subject':'Math'},
{'StId':6,'StName':'Kit','Class':'6','Subject':'Science'},
{'StId':7,'StName':'Albert','Class':'8','Subject':'Math'}
]);
ko.applyBindings(viewModel);
body{
background-color: white;
}
.subjectHeader{
font-weight: bolder;
font-size: 14px;
}
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.2/knockout-min.js"></script>
<table class='table table-condensed table-bordered'>
<thead>
<th>St Id</th>
<th>St Name</th>
<th>Class</th>
<th>Subject</th>
</thead>
<!--<tbody data-bind='foreach: viewModel.SubjectClass'>-->
<tbody data-bind='foreach: viewModel.Subject'>
<tr><td colspan="4">
<p class="subjectHeader">
<!--<span data-bind="text:Class"></span>
<span data-bind='text:Subject' style="margin-left: 40%;"></span>-->
<span data-bind='text:$data' style="margin-left: 40%;"></span>
</p>
<table class='table table-condensed table-bordered'>
<tbody data-bind="foreach:viewModel.Students">
<!--<tr data-bind="if: Subject == $parentContext.Subject">-->
<tr data-bind="if: Subject == $parentContext.$data">
<td data-bind='text:StId'></td>
<td data-bind='text:StName'></td>
<td data-bind='text:Subject'></td>
<td data-bind='text:Class'></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
我理解这个问题是因为$parentContext因为它没有 observableArray 的引用,这就是为什么 'Subject' 数组正在工作,但没有 SubjectClass 用于绑定子循环。我评论了不工作的部分。
解决方案
您只需要使用$parent
保存实际数据的 ,而不是对$parentContext
绑定上下文的引用。
var viewModel={};
viewModel.Subject=ko.observableArray(['Science','Math']);
viewModel.SubjectClass=ko.observableArray([{'Class':'8','Subject':'Science'},{'Class':'7','Subject':'Math'},{'Class':'8','Subject':'Science'},{'Class':'6','Subject':'Math'}]);
viewModel.Students=ko.observableArray([
{'StId':1,'StName':'John','Class':'8','Subject':'Science'},
{'StId':2,'StName':'Martha','Class':'7','Subject':'Math'},
{'StId':3,'StName':'George','Class':'6','Subject':'Math'},
{'StId':4,'StName':'Martin','Class':'8','Subject':'Science'},
{'StId':5,'StName':'Donny','Class':'7','Subject':'Math'},
{'StId':6,'StName':'Kit','Class':'6','Subject':'Science'},
{'StId':7,'StName':'Albert','Class':'8','Subject':'Math'}
]);
ko.applyBindings(viewModel);
body{
background-color: white;
}
.subjectHeader{
font-weight: bolder;
font-size: 14px;
}
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.2/knockout-min.js"></script>
<table class='table table-condensed table-bordered'>
<thead>
<th>St Id</th>
<th>St Name</th>
<th>Class</th>
<th>Subject</th>
</thead>
<tbody data-bind='foreach: viewModel.SubjectClass'>
<!--<tbody data-bind='foreach: viewModel.Subject'>-->
<tr><td colspan="4">
<p class="subjectHeader">
<span data-bind="text:Class"></span>
<span data-bind='text:Subject' style="margin-left: 40%;"></span>
<!--<span data-bind='text:$data' style="margin-left: 40%;"></span>-->
</p>
<table class='table table-condensed table-bordered'>
<tbody data-bind="foreach:viewModel.Students">
<tr data-bind="if: Subject == $parent.Subject">
<!--<tr data-bind="if: Subject == $parentContext.$data">-->
<td data-bind='text:StId'></td>
<td data-bind='text:StName'></td>
<td data-bind='text:Subject'></td>
<td data-bind='text:Class'></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
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