knockout.js输入框事件更改 - 传递旧值

When adding a change event binding to an input box using knockout.js the old value is passed to the change function when the event is fired. I can work around this by using blur. Is this the intended behavior? Is the idea to use the change event to have the old value and then use a normal selector to get the value from the dom? It seems counter intuitive.

使用knockout.js将更改事件绑定添加到输入框时,会在触发事件时将旧值传递给change函数。我可以通过使用模糊来解决这个问题。这是预期的行为吗?是否使用change事件来获取旧值,然后使用普通选择器从dom获取值?这似乎反直觉。

jsFiddle Example

JavaScript
----------
var data = {
    saved_value:"1",
    value_changed: function(data){
        alert(data.saved_value());
    }
};
var viewModel = ko.mapping.fromJS(data);
ko.applyBindings(viewModel);

HTML
----
Current Value:<span data-bind="text:saved_value"></span><br/>
<input data-bind="event:{change:value_changed},value:saved_value"></input>

4 个解决方案

#1

Try using the text and value bindings:

尝试使用文本和值绑定:

Current Value:<span data-bind="text: saved_value"></span><br/>
<input data-bind="value: saved_value"></input>

And change the JavaScript to this:

并将JavaScript更改为:

var data = {
    saved_value: "1"    
};

var viewModel = ko.mapping.fromJS(data);
ko.applyBindings(viewModel);

Here's an associated jsFiddle: http://jsfiddle.net/6zmJs/

这是一个相关的jsFiddle:http://jsfiddle.net/6zmJs/

If you want to alert() the value of saved_value when it is updated you could use ko.computed or viewModel.saved_value.subscribe(function(value) { alert(value); }); -- although those aren't the only ways to do this.

如果你想更新saved_value的值,你可以使用ko.computed或viewModel.saved_value.subscribe(function(value){alert(value);}); - 虽然这些不是唯一的方法。

#2

Update: For newer versions of knockout, you can replace the value binding with textInput, which handles many edge cases not covered by valueUpdate.

更新:对于较新版本的knockout,您可以使用textInput替换值绑定,textInput处理valueUpdate未涵盖的许多边缘情况。

No, this is not the right way to do things.

不,这不是正确的做事方式。

You're getting the old value because saved_value doesn't get updated until the textbox loses focus.

您将获得旧值,因为saved_value在文本框失去焦点之前不会更新。

If you want to push the new value in as the user types, using the valueUpdate option of the input binding:

如果要在用户键入时使用输入绑定的valueUpdate选项推送新值:

<input data-bind="event: { change: value_changed }, value: saved_value, valueUpdate: 'afterkeydown'" />

The valueUpdate option takes an event name (e.g. 'keyup'). When that event fires, your saved_value will be updated.

valueUpdate选项采用事件名称(例如'keyup')。当该事件触发时,您的saved_value将被更新。

Now let me propose an alternate solution.

现在让我提出一个替代解决方案。

Still do the valueUpdate binding like I showed above, but instead of listening for the changed event, just subscribe to the observable:

仍然像我上面所示的那样执行valueUpdate绑定,但是不是监听已更改的事件,只需订阅observable:

<input data-bind="textInput: saved_value" />

Then in JS:

然后在JS中:

var viewModel = {
    saved_value: ko.observable("1"),
};
viewModel.saved_value.subscribe(function (newValue) {
   alert(data.saved_value());
});
ko.applyBindings(viewModel);

#3

If you put the 'event' option at the end you don't need the 'valueUpdate' option. Like this:

如果您将'event'选项放在最后,则不需要'valueUpdate'选项。喜欢这个:

<input data-bind="value: saved_value, event: { change: value_changed }" />

Also note that when you make use of subscribe to an observable, it gets triggered every time your value changes. (either by user interaction or programmatically).

另请注意,当您使用订阅可观察对象时,每次您的值更改时都会触发它。 (通过用户交互或以编程方式)。

#4

Try this in the data bind write event handlers, after the value handlers and not before:

在数据绑定写事件处理程序中尝试此操作,在值处理程序之后而不是之前:

<input data-bind="value: property, event:{ change: doSomething}" />

#1