使用 Knockout-ES5 时如何访问自定义绑定中的可观察对象

Question

如果模型属性是 ko.observable()，则可以在自定义绑定中按如下方式访问这些属性。

var observable = valueAccessor();

当使用 Knockout-ES5 插件时，如何在自定义绑定中获取 observable？检查下面的代码并查找注释“如何在此处获取 propertyName？”

JS Fiddle when not using Knockout-ES pluginAnother Look at Custom Bindings for KnockoutJS 友情提供

Updated fiddle with model changed to use Knockout-ES plugin

ko.bindingHandlers.datepicker = {
    init: function(element, valueAccessor, allBindingsAccessor, viewModel) {
        //initialize datepicker with some optional options
        var options = allBindingsAccessor().datepickerOptions || {};
        $(element).datepicker(options);

        //handle the field changing
        ko.utils.registerEventHandler(element, "change", function () {
            var observable = valueAccessor();
            if (!ko.isObservable(observable)) {                
                console.log("Not Observable");
                //How to get propertyName here?
                //ko.getObservable(viewModel, 'propertyName');
                return;
            }
            observable($(element).datepicker("getDate"));
        });

        //handle disposal (if KO removes by the template binding)
        ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
            $(element).datepicker("destroy");
        });

    },
    //update the control when the view model changes
    update: function(element, valueAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor()),
            current = $(element).datepicker("getDate");

        if (value - current !== 0) {
            $(element).datepicker("setDate", value);   
        }
    }
};

var viewModel = {
    myDate: new Date("11/01/2011"),
    setToCurrentDate: function() {
       this.myDate = new Date();   
    }
};

ko.track(viewModel);

ko.applyBindings(viewModel);

Answer 1

您可以将实际的 observable 传递给绑定：

data-bind="datepicker: ko.getObservable($data, 'myDate') ..."

http://jsfiddle.net/xb6vR/1/

但这很难看。幸运的是，Knockout 确实提供了一种方法（未记录）从绑定中写入属性值：

//handle the field changing
ko.utils.registerEventHandler(element, "change", function () {
    var writable = valueAccessor();
    if (!ko.isObservable(writable)) {                
        var propWriters = allBindingsAccessor()._ko_property_writers;
        if (propWriters && propWriters.datepicker) {
            writable = propWriters.datepicker;
        } else {
            return;
        }
    }
    writable($(element).datepicker("getDate"));
});

http://jsfiddle.net/xb6vR/3/

Answer 2

我最终使用了传递属性名和回退到 _ko_property_writers 的组合。 JS Fiddle.

HTML

<input data-bind="datepicker: myDate, datePropertyName: 'myDate',
       datepickerOptions: { minDate: new Date() }" />

Javascript

ko.bindingHandlers.datepicker = {
    init: function(element, valueAccessor, allBindingsAccessor, viewModel) {
        var _viewModel = viewModel;
        //initialize datepicker with some optional options
        var options = allBindingsAccessor().datepickerOptions || {};
        $(element).datepicker(options);

        //handle the field changing
        ko.utils.registerEventHandler(element, "change", function () {
            var observable = valueAccessor();
            if (!ko.isObservable(observable)) {                
                console.log("Not Observable");
                var datePropertyName = allBindingsAccessor().datePropertyName;

                if (datePropertyName) {
                    console.log("Using datePropertyName");
                    observable = ko.getObservable(_viewModel, datePropertyName);
                }
                else {
                    console.log("No datePropertyName, trying _ko_property_writers");
                    var propWriters = allBindingsAccessor()._ko_property_writers;

                    if (propWriters && propWriters.datepicker) {
                        observable = propWriters.datepicker;
                    } else {
                        console.log("No way to get observable");
                        return;
                    }
                }
            }
            observable($(element).datepicker("getDate"));
        });

        //handle disposal (if KO removes by the template binding)
        ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
            $(element).datepicker("destroy");
        });

    },
    //update the control when the view model changes
    update: function(element, valueAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor()),
            current = $(element).datepicker("getDate");

        if (value - current !== 0) {
            $(element).datepicker("setDate", value);   
        }
    }
};

var viewModel = {
    myDate: new Date("11/01/2011"),
    setToCurrentDate: function() {
       this.myDate = new Date();   
    }
};

ko.track(viewModel);

ko.applyBindings(viewModel);

Answer 3

作为对 Michael Best 回答的补充，如果您将 knockoutjs 3.0 与 es5 插件一起使用，则无法使用 allBindingsAccessor()._ko_property_writers; 访问 observable 但是我发现可以使用ko.getObservable 函数访问它。所以它应该是这样的：

ko.bindingHandlers.myCustomBinder = {
    init: function (element, valueAccessor, allBindingsAccessor, context) {
        var observable = ko.getObservable(context, 'observableName');
    }
}

Answer 4

好吧，您可以使用预处理来放置 getObservable 并在绑定处理程序中正常使用它。

preprocess: function (markup: string) {
        console.log("markup", markup);

        var lastDotIndex = markup.lastIndexOf('.');

        if (lastDotIndex > 0) {
            var obj = markup.substring(0, lastDotIndex);
            var property = markup.substring(lastDotIndex + 1);

            return 'ko.getObservable(' + obj + ', \'' + property + '\');';

        } else {
            return 'ko.getObservable($data, \'' + markup + '\')';
        }
    },

Answer 5

function es5Preprocess(val){
    var alt = val.split('.');
    var tail = alt.pop();
    if(alt.length == 0) alt.push('$data');
    tail = 'ko.getObservable( ' + alt.join('.') + ', ' + '\'' + tail + '\'' + ' )';
    return tail + ' || ' + val;
};
window.ko.es5.customBinding = function(name, binding){
    binding.preprocess = es5Preprocess;
    window.ko.bindingHandlers[name] = binding;
};

然后

window.ko.es5.customBinding('contentEditable', {
    init: function(element, valueAccessor) {
        var val = valueAccessor();
        element.onblur = function() {
            val(element.textContent);
        };
    },
    update: function(element, valueAccessor) {
        element.textContent = valueAccessor()();
    }
});