Knockout.js扩展与拦截器的值绑定

Question

这似乎是在绑定到输入字段时使用knockout清理/验证/格式化数据的常用方法，它创建了一个使用计算的observable的可重用自定义绑定。 它基本上扩展了默认值绑定，以包括一个拦截器，它将在写入/读取之前格式化/清理/验证输入。

ko.bindingHandlers.amountValue = {
  init: function (element, valueAccessor, allBindingsAccessor) {
    var underlyingObservable = valueAccessor();

    var interceptor = ko.computed({
      read: function () {
        // this function does get called, but it's return value is not used as the value of the textbox.
        // the raw value from the underlyingObservable is still used, no dollar sign added. It seems like 
        // this read function is completely useless, and isn't used at all
        return "$" + underlyingObservable();
      },

      write: function (newValue) {
        var current = underlyingObservable(),
            valueToWrite = Math.round(parseFloat(newValue.replace("$", "")) * 100) / 100;

        if (valueToWrite !== current) {
          // for some reason, if a user enters 20.00000 for example, the value written to the observable
          // is 20, but the original value they entered (20.00000) is still shown in the text box.
          underlyingObservable(valueToWrite);
        } else {
          if (newValue !== current.toString())
            underlyingObservable.valueHasMutated();
        }
      }
    });

    ko.bindingHandlers.value.init(element, function () { return interceptor }, allBindingsAccessor);
  },

  update: ko.bindingHandlers.value.update
};

jsFiddle示例： http ： //jsfiddle.net/6wxb5/1/

我错过了什么吗？ 我已经看到这种方法在任何地方使用，但它似乎没有完全奏效。 read函数似乎完全无用，因为它根本没有被使用..在write函数中，输入“23.0000”会将写入值更改为23，但文本框值不会更新。

Answer 1

问题来自自定义绑定的update部分。 此部分将根据原始模型值更新字段。 因此， init附加的事件处理程序将通过可写入的计算机发送新值，但实际上update时会update字段。

一个选项是从init函数应用值绑定并跳过update函数，如：

ko.bindingHandlers.amountValue = {
  init: function (element, valueAccessor, allBindingsAccessor) {
    var underlyingObservable = valueAccessor();

    var interceptor = ko.computed({
      read: function () {
        // this function does get called, but it's return value is not used as the value of the textbox.
        // the raw value from the underlyingObservable, or the actual value the user entered is used instead, no   
        // dollar sign added. It seems like this read function is completely useless, and isn't used at all
        return "$" + underlyingObservable();
      },

      write: function (newValue) {
        var current = underlyingObservable(),
            valueToWrite = Math.round(parseFloat(newValue.replace("$", "")) * 100) / 100;

        if (valueToWrite !== current) {
          // for some reason, if a user enters 20.00000 for example, the value written to the observable
          // is 20, but the original value they entered (20.00000) is still shown in the text box.
          underlyingObservable(valueToWrite);
        } else {
          if (newValue !== current.toString())
            underlyingObservable.valueHasMutated();
        }
      }
    });

      ko.applyBindingsToNode(element, { value: interceptor });
  }
};

更新小提琴： http ： //jsfiddle.net/rniemeyer/Sr8Ev/