淘汰赛:编写和读取计算属性 [英] Knockout: writing and reading a computed property

问题描述

我有一个具有两个属性的模型:标题和内容，我想做的是:

I have a model with two property: title and content and what I want to do is:

如果title具有值，请使用它，但如果其为空白，请使用内容的前20个字符+"...".

If title has a value, use it but in case it's blank use the first 20 chars + "..." from content.

这是模型:

       function Note(title, content) {
        var self = this;

        self.content = ko.observable(content);
        self.title = ko.computed({
          read: function(){
            if(!title){
              var content = self.content();
              if(content) return content.substring(0,19) + "...";
            }
          },
          write: function(title){
           return title;
          }
        });
       }

标题值已从内容中正确更新，但对我而言，不可能直接写标题.

Title value gets correctly updated from content but it's impossible (for me) to get writing directly on title working..

RP Niemeyer回答中的唯一问题是，我只能拥有用于读/写的属性，这可能吗?

推荐答案

在创建可写的可计算观察值时，您将需要一个单独的观察值来包含实际标题.

When creating your writeable computed observable, you will want to have a separate observable to contain the actual title.

更像是:

function Note(title, content) {
    var self = this;

    self.content = ko.observable(content);
    self.title = ko.observable(title);

    self.displayTitle = ko.computed({
        read: function() {
            var title = self.title();
            if (!title) {
                var content = self.content();
                if (content) return content.substring(0, 19) + "...";
            }

            return title;
        },
        write: self.title
    });
}​

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