敲除Select2按对象设置初始值

时间：2018-09-18 03:49:17

标签： html select knockout.js jquery-select2 dropdown

我有一个Knockout.js Web应用程序，其中有一个select2下拉菜单。我想将id和text值都绑定到变量上，而不仅仅是id。这是我的数据：

var cars = [{id: 1, name: 'Honda'}, {id: 2, name: 'Toyota'}, {id: 3, name: 'Dodge'}];
var selectedCar = ko.observable();

这是我的html：

<select data-bind="value: selectedCar, optionsCaption: 'Select', optionsText: 'name', options: cars"></select>

现在，每当我在下拉列表中选择某项时，我的变量就包含整个对象，如下所示：

selectedCar = {id: 1, name: 'Honda'};

唯一的问题是在您加载页面并希望将下拉菜单设置为特定值时发生。即使在呈现html之前将selectedCar变量设置为{id: 1, name: 'Honda'}（当页面呈现下拉菜单时）并未设置为任何值，它只是设置为占位符“选择”。

我在做什么错了？

2 个答案:

答案 0 :(得分：1)

如果要将id和text值都绑定到变量，则需要使用optionsValue绑定并将整个上下文绑定到该变量（$data）; 

<select data-bind="value: selectedCar, 
                   optionsCaption: 'Select', 
                   optionsText: 'name', 
                   options: cars, 
                   optionsValue: $data"></select>

通常，我们将指定ID或其他以获得初始值的内容。因此，在您的问题中，如果将湿对象集{id: 1, name: 'Honda'}而不是selectedCar设置为optionsValue: $data，则将整个对象$optionsValue: 'id'作为初始值提供给cars就很有意义。

（重要）但事实证明这是行不通的，因为我们正在创建一个新对象，因此当Knockout的相等性测试将selectedCar的对象与cars[0]中的对象。设置初始值的正确方法是this。

我确定这是一个错字，但是无论如何我都会指定：创建任何需要HTML访问的变量时，您需要将其绑定到this.cars = [{id: 1, name: 'Honda'}, {id: 2, name: 'Toyota'}, {id: 3, name: 'Dodge'}]; this.selectedCar = ko.observable(); ，这将是对viewModel。

var viewModel = function(){
  var self = this;
  self.cars = [{id: 1, name: 'Honda'}, {id: 2, name: 'Toyota'}, {id: 3, name: 'Dodge'}];
  self.selectedCar = ko.observable(self.cars[0]);
  

};

ko.applyBindings(new viewModel());

让我们用小提琴测试所有这些：

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.2/knockout-min.js"></script>
<select data-bind="value: selectedCar, optionsCaption: 'Select', optionsText: 'name', optionsValue:$data, options: cars"></select>

<!-- to verify that we are getting the entire object -->
<p data-bind="text: ko.toJSON(selectedCar)"></p>
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1: File: latin2.xml,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\charsets\,  Size: 7651
1: File: latin5.xml,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\charsets\,  Size: 5928
1: File: latin7.xml,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\charsets\,  Size: 7851
1: File: macce.xml,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\charsets\,  Size: 8460
1: File: macroman.xml,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\charsets\,  Size: 8471
1: File: README,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\charsets\,  Size: 1749
1: File: swe7.xml,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\charsets\,  Size: 6943
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\czech\,  Size: 259348
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\danish\,  Size: 259348
1: File: dictionary.txt,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 25575
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\dutch\,  Size: 260368
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\english\,  Size: 258589
1: File: errmsg-utf8.txt,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 826306
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\estonian\,  Size: 258853
1: File: fill_help_tables.sql,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 1023732
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\french\,  Size: 259996
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\german\,  Size: 266283
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\greek\,  Size: 265380
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\hungarian\,  Size: 259230
1: File: innodb_memcached_config.sql,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 3999
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\italian\,  Size: 260359
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\japanese\,  Size: 266035
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\korean\,  Size: 261629
1: File: mysql_sys_schema.sql,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 289722
1: File: mysql_system_tables.sql,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 109850
1: File: mysql_system_tables_data.sql,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 5510155
1: File: mysql_system_users.sql,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 2289
1: File: mysql_test_data_timezone.sql,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\,  Size: 10830
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\norwegian\,  Size: 258659
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\norwegian-ny\,  Size: 258712
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\polish\,  Size: 259518
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\portuguese\,  Size: 261549
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\romanian\,  Size: 260301
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\russian\,  Size: 273927
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\serbian\,  Size: 260970
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\slovak\,  Size: 259115
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\spanish\,  Size: 260243
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\swedish\,  Size: 259442
1: File: errmsg.sys,  Directory: C:\Program Files\MySQL\MySQL Server 8.0\share\ukrainian\,  Size: 268501
1: Action 23:38:59: CreateShortcuts. Creating shortcuts
1: Shortcut: icon.ico
1: Shortcut: Icon.MysqlCmdShell
1: Shortcut: rpxm3ds_|MySQL 8.0 Command Line Client
1: Shortcut: 7ejegqmo|MySQL 8.0 Command Line Client - Unicode
1: Action 23:38:59: WriteRegistryValues. Writing system registry values
1: Key: \SOFTWARE\MySQL AB\MySQL Server 8.0, Name: Location, Value: C:\Program Files\MySQL\MySQL Server 8.0\
1: Key: \SOFTWARE\MySQL AB\MySQL Server 8.0, Name: Version, Value: 8.0.12
1: Key: \SOFTWARE\MySQL AB\MySQL Server 8.0, Name: DataLocation, Value: C:\ProgramData\MySQL\MySQL Server 8.0\
1: Key: \SOFTWARE\MySQL AB\MySQL Server 8.0, Name: , Value: 
1: Key: \Console\MySQL 8.0 Command Line Client - Unicode, Name: FaceName, Value: Lucida Console
1: Key: \Console\MySQL 8.0 Command Line Client - Unicode, Name: FontWeight, Value: #400
1: Key: \Console\MySQL 8.0 Command Line Client - Unicode, Name: , Value: 
1: Key: \Software\MySQL AB\MySQL Server 8.0, Name: installed, Value: #1
1: Action 23:38:59: ExecSecureObjects. 
1: Action 23:38:59: Rollback. Rolling back action:
1: ExecSecureObjects
1: Writing system registry values
1: Creating shortcuts
1: Copying new files
1: Creating folders
1: Updating component registration
1: 1: MySQL Server 8.0 2: {29AEA9CC-3A6A-4F86-8A0E-AC8750F91B69} 3: 3 
1: The action 'Install' for product 'MySQL Server 8.0.12' failed.

答案 1 :(得分：0)

选择框的value将成为与所选项目或optionsValue参数中设置的属性相对应的对象。因此，对于对象，您设置的所选值必须与数组中存在的实例相同。具有对象的不同实例恰好在结构上等效是不够的。

在这种情况下，我发现将选择框的值绑定到对象的唯一ID更容易。然后，您可以通过计算值将该ID映射到所需的实际实例。

function ViewModel(data) {
    this.cars = data.cars;
    this.selectedCarId = ko.observable(data.selectedCarId);
    this.selectedCar = ko.computed(() => {
        let selectedCarId = this.selectedCarId();
        return this.cars.find(c => c.id === selectedCarId);
    });
}

let model = {
    cars: [
        { id: 1, name: 'Honda' },
        { id: 2, name: 'Toyota' },
        { id: 3, name: 'Dodge' }
    ],
    selectedCarId: 2
};
ko.applyBindings(new ViewModel(model), document.getElementById('content'));
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.5/js/select2.min.js"></script>
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.5/css/select2.min.css">
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.2/knockout-min.js"></script>

<div id="content">
  <select data-bind="value: selectedCarId,
                     optionsCaption: 'Select',
                     optionsText: 'name',
                     optionsValue: 'id',
                     options: cars">
  </select>
  <p>selectedCarId: <span data-bind="text: selectedCarId"></span></p>
  <p>selectedCar: <span data-bind="text: ko.toJSON(selectedCar)"></span></p>
  
  <pre data-bind="text: ko.toJSON($root, null, 2)"></pre>
</div>

如果您不想使用单独的计算属性，则仍然需要传递索引，但是必须从数组中获取设置的值。

function ViewModel(data) {
    this.cars = data.cars;
    this.selectedCar = ko.observable(
        data.cars.find(c => c.id === data.selectedCarId)
    );
}
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