我怎样才能使淘汰赛“价值”绑定只写，这样它就不会尝试从中读取？

Question

<input data-bind="value: fileName" type="file" multiple="">
<input data-bind="value: fileName" type="text" readonly="">

This works except I get:

Uncaught InvalidStateError: Failed to set the 'value' property on 'HTMLInputElement': This input element accepts a filename, which may only be programmatically set to the empty string.

because it tries to set the value of the file input when I only want to read it and write it to the text input.

Example

http://jsfiddle.net/esk5akwj/2/

• Check box.
• Choose a file.
• Check box again.
• Try to choose a file again.

Answer 1

Since the file chooser value can only be set by using the file chooser, and must start as the empty string, you need a custom binding handler that wraps the value binding and on init sets the bound value to the empty string:

 ko.bindingHandlers.resetValue = { init: function(element, valueAccessor, allBindingsAccessor, data, context) { valueAccessor()(''); ko.bindingHandlers.value.init(element, valueAccessor, allBindingsAccessor, data, context); }, update: function(element, valueAccessor, allBindingsAccessor, data, context) { ko.bindingHandlers.value.update(element, valueAccessor, allBindingsAccessor, data, context); } }; ko.applyBindings({ fileName: ko.observable(), c: ko.observable() });

 <script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script> <input data-bind="checked: c" type="checkbox">Check me, choose a file, uncheck me, check me, choose a file. <!-- ko if: c --> <input data-bind="resetValue: fileName" type="file" multiple=""> <input data-bind="value: fileName" type="text" readonly> <!-- /ko -->