II 创建了一个文本计数器来告诉用户他们已经输入了多少字符以及还有多少字符可用。这应该显示文本区域何时具有焦点并消失,然后文本区域失去焦点。
我创建了一个绑定处理程序,它使用扩展器来扩展传递给它的可观察对象。问题是它只有在输入文本、导航离开文本区域,然后导航回文本区域后才能工作。
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
</head>
<body>
<div class="question" >
<label for="successes" data-textkey="successes">This is a question</label>
<textarea data-bind="textCounter: successes, hasFocus: successes.hasFocus, maxLength:200, event: { keyup:successes.updateRemaining }"></textarea>
<div class="lengthmessage edit" data-bind="visible:successes.hasFocus()">
<div >
<em>Length:</em> <span data-bind="text:successes.currentLength"></span>
<em>Remaining:</em> <span data-bind="text:successes.remainingLength"></span>
</div>
</div>
</div>
<script src="../Scripts/knockout-2.3.0.debug.js" type="text/javascript"></script>
<script type="text/javascript">
(function (ko) {
ko.extenders.textCounter = function (target, options) {
options = options || {};
options.maxLength = options.maxLength ? parseInt(options.maxLength) : 2000;
target.maxLength = ko.observable(options.maxLength);
target.currentLength = ko.observable(target().length);
target.remainingLength = ko.observable(target.maxLength() - target.currentLength());
target.hasFocus = ko.observable(false);
target.hasFocus.subscribe(function () {
target.currentLength(target().length);
target.remainingLength(target.maxLength() - target.currentLength());
});
target.updateRemaining = function (data, event) {
if (event.target == undefined && event.srcElement.value == "") {
target.currentLength(0);
}
else {
var e = $(event.target || event.srcElement);
target.currentLength(e.val().length);
if (target.currentLength() > target.maxLength()) {
e.val(e.val().substr(0, target.maxLength()));
target.currentLength(target.maxLength());
}
}
target.remainingLength(target.maxLength() - target.currentLength());
};
return target;
};
ko.bindingHandlers.textCounter = {
init: function (element, valueAccessor, allBindingsAccessor, viewModel) {
var val = ko.utils.unwrapObservable(valueAccessor());
var observable = valueAccessor();
observable.extend({ textCounter: allBindingsAccessor() });
ko.applyBindingsToNode(element, {
value: valueAccessor()
});
},
update: function (element, valueAccessor, allBindingsAccessor, viewModel) {
var val = ko.utils.unwrapObservable(valueAccessor());
var observable = valueAccessor();
ko.bindingHandlers.css.update(element, function () { return { hasFocus: observable.hasFocus }; });
}
};
var viewModel = function () {
this.successes = ko.observable("");
//this.successes.hasFocus = ko.observable();
}
ko.applyBindings(new viewModel());
} (ko));
</script>
</body>
</html>
如果我取消注释:
//this.successes.hasFocus = ko.observable();
从一开始,页面就会按照我想要的方式运行,但是它违背了使用扩展器的全部目的,因为我的视图模型现在有一个来自扩展器的对象。
我必须相信我在这里缺少一些相对简单的东西。
谢谢你的帮助..