javascript - 将 View 模型绑定(bind)到 knockout 中属性的存在

Question

我正在使用 Knockout.js 填充一组 HTML5 <details>元素。这是结构:

<div class="items" data-bind="foreach: Playlists">
    <details class="playlist-details" data-bind="attr: {id: 'playlist-details-' + $index()}">
        <summary>
            <span data-bind="text: name"></span> - <span data-bind="text: count"></span> item(s)
            <div class="pull-right">
                <button data-bind="click: $parent.play, css: {disabled: count() == 0}, attr: {title: playbtn_title}" class="btn"><i class="icon-play"></i> Play</button>
                <button data-bind="click: $parent.deleteList" class="btn btn-danger"><i class="icon-trash"></i> Delete</button>
            </div>
        </summary>
        <div class="list" data-bind="with: items" style="padding-top: 2px;">
            ...
        </div>
    </details>
</div>

ViewModel 中的数据看起来像这样:

var VM = {
    Playlists: [
        {
            name: "My Playlist1",
            count: 3,
            items: [<LIST OF SONG ID'S>],
            playbtn_title: "Play this playlist"
        },
        {
            name: "My Playlist2",
            count: 5,
            items: [<LIST OF SONG ID'S>],
            playbtn_title: "Play this playlist"
        },
        {
            name: "My Playlist3",
            count: 0,
            items: [],
            playbtn_title: "You need to add items to this list before you can play it!"
        }
    ]
};

我想添加记住 open or closed state 的能力的详细信息 View 。我之前使用 jQuery 实现了此行为和 localStorage ¹，但对于这个项目，我想原生使用 Knockout 而不是使用 jQuery。

我添加了一个 isOpen从 localStorage 检索到的 ViewModel 中播放列表的属性页面加载时。但是，我似乎无法使用 attr在 Knockout 中绑定(bind)，因为 HTML5 spec说只寻找 presence or absence的 open属性，而不是值。

如何让 Knockout 添加和删除 open <details> 的属性(property)元素为 isOpen ViewModel 的属性改变了吗？

---

¹:像这样:

// On the initial page load.
contents += '<details ' + ((localStorage['tl_open_playlist-details-' + counter] == 1) ? 'open' : '') ' class="playlist-details" id="playlist-details-' + counter + '" data-name="' + escape(listname) + '">'

...

// Update storage when things are clicked.
$(document).on('DOMSubtreeModified', 'details.playlist-details', function() {
    if ($(this).prop('open')) {
        localStorage['tl_open_' + this.id] = 1;
    } else {
        delete localStorage['tl_open_' + this.id];
    }
});

Answer 1

您可以修改 attr 绑定(bind)以考虑另一个绑定(bind)选项(此处名为 attrRemoveWhenFalse)并为您删除该属性:

<input class='testInput' type="text" 
       data-bind="attr: { disabled: isDisabled }, attrRemoveWhenFalse: true" />

var originalAttr = { init: ko.bindingHandlers.attr.init, 
                     update: ko.bindingHandlers.attr.update }
ko.bindingHandlers.attr.update = function (element, valueAccessor, 
                                           allBindingAccessor, viewModel, 
                                           bindingContext) {
    if (typeof originalAttr.update === 'function') 
        originalAttr.update(element, valueAccessor, allBindingAccessor, 
                            viewModel, bindingContext);
    if (allBindingAccessor().attrRemoveWhenFalse) {
        for (var prop in valueAccessor()) {
            if (!ko.utils.unwrapObservable(valueAccessor()[prop])) {
                element.removeAttribute(prop);
            }
        }
    }
}

Demo