Question

我认为对于淘汰赛专家来说，这对我来说是一个简单的问题，这让人感到困惑。

我的JSON输入：

    {
      "odata.metadata":"http://localhost:49163/odata/$metadata#TwitterMessages","value":[
        {
          "message":{
            "text":"Pellentesque fermentum a diam a suscipit. Donec ultrices tempor sapien, vitae dictum erat pulvinar sagittis. Vivamus a fermentum lectus, et lacinia enim. Morbi pretium adipiscing risus, vitae euismod lacus fermentum eu.","company_fk":3,"image_url":"http://www.baconwrappedmedia.com/wp-content/uploads/2013/01/funny-kids-bacon-wrapped-media-21.jpg","active":true,"author_id":"3242342423","message_id":3,"author_picture":"http://3.bp.blogspot.com/_Gxh8CVH8l8Y/TJBDI4QVfnI/AAAAAAAAAWE/W1H4Z2MAub0/s1600/547206_1271901770610.27res_400_483.jpg","author_name":"Ligula","source":"TWITTER","createddatefriendly":"1 day ago","message":"Ut at erat at mauris euismod tincidunt non id justo?","pubdate":"2014-01-10T13:27:42.917"
          },"hashtag":{
            "hashtag_id":2,"hashtag":"#voetbal","company_fk":3
          },"twitter_id":"0","user_screenname":"Ligula","user_name":"Ligula","message_fk":3,"hashtag_fk":2
        },{
          "message":{
            "text":"Duis sed nunc semper, volutpat urna et, volutpat diam.","company_fk":3,"image_url":"http://www.allfunnystuff.com/wp-content/uploads/2013/04/funny-baby-angry-punch.jpg","active":true,"author_id":"75675675","message_id":4,"author_picture":"http://www.drodd.com/images8/funny-face15.jpeg","author_name":"Curabitur","source":"TWITTER","createddatefriendly":"3 day(s) ago","message":"Suspendisse a sapien id lorem tincidunt imperdiet eget id velit.","pubdate":"2014-01-10T13:30:26.657"
          },"hashtag":{
            "hashtag_id":2,"hashtag":"#voetbal","company_fk":3
          },"twitter_id":"0","user_screenname":"Curabitur","user_name":"Curabitur","message_fk":4,"hashtag_fk":2
        }
      ]
    }

我的javascript / Knockout代码：

    function CompanyViewModel() {
        var self = this;
        self.name = ko.observable();
    }

    function TweetViewModel(item) {
        var self = this;
        self.user_screenname = ko.observable("");
        self.user_name = ko.observable("");
        self.message = ko.observable("");
        self.hashtag = ko.observable("");
        ko.mapping.fromJS(item, {}, self);
    }

    function ViewModel() {
        var self = this;
        self.Company = ko.observable(new CompanyViewModel());
        self.Tweets = ko.observableArray([new TweetViewModel()]);

        $.getJSON('/Data/company.json', function (data) {
            ko.mapping.fromJS(data, {}, self.Company());
        });

        $.getJSON('/Data/tweets.json', function (allData) {
            var mappedTweets = $.map(allData.value, function (item) {
                return new TweetViewModel(item)
            });
            self.Tweets(mappedTweets);

            console.log(self.Tweets())
        });
    }

    var vm = new ViewModel();

    ko.applyBindings(vm);

我的HTML：

    <tbody data-bind="foreach: Tweets">
        <tr>
            <td data-bind="text: user_screenname"></td>
            <td data-bind="text: message().text"></td>
            <td data-bind="text: hashtag().hashtag"></td>
        </tr>
    </tbody>

一切都很好。但这是我的问题：

为什么我不需要“声明”Message.Text observable来使用它进行数据绑定，但是我需要声明user_screenname是否可观察？

如果我删除该行：

        self.user_screenname = ko.observable("");

我收到错误：未定义user_screenname。当我使用映射构造时，我希望user_screenname属性也自动映射到viewmodel。或者我做错了什么？

Answer 1

您需要明确声明您的user_screenname，因为返回数据中的某个message不包含user_screenname属性，因此映射不会创建它，您的绑定也会中断。

您可以使用$data：

为您的财产添加前缀

<td data-bind="text: $data.user_screenname"></td>`

在这种情况下，如果您没有user_screenname属性，绑定将不会中断，因此它可以在不明确声明user_screenname的情况下工作。

淘汰不是所有属性都被映射

1 个答案: