输入值的敲除力更新答案

【问题标题】：Knockout force update of input value输入值的敲除力更新
【发布时间】：2013-08-02 23:01:57
【问题描述】：

我的页面上有一个使用值绑定具有可观察绑定的输入。但是，如果新值小于指定的字符数，我有一个扩展器会阻止对可观察对象的写入：

ko.extenders.minLengthRevert = function(target, minLength) {
    "use strict";

    //create a write able computed observable to intercept writes to our observable
    var result = ko.computed({
        read: target,  //always return the original observables value
        write: function(newValue) {
            var current = target();
            if (current !== newValue){
                if (newValue.length >= minLength){
                    target(newValue);
                }
            }
        }
    });

    //return the new computed observable
    result(target());
    return result;
};

这很好用，除非我清除输入框的值，否则该框不会恢复为旧值（但 observable 不会正确更新）。所以基本上我需要一些方法来强制输入框从 observable 更新，即使 observable 没有更新。这是一个演示行为的 JSFiddle：http://jsfiddle.net/4Z5bp/

【问题讨论】：

标签： knockout.js

【解决方案1】：

添加“else { target.notifySubscribers(current); }”子句。这将诱使文本框认为值已更改并自行重置：

ko.extenders.minLengthRevert = function(target, minLength) {
    "use strict";

    //create a write able computed observable to intercept writes to our observable
    var result = ko.computed({
        read: target,  //always return the original observables value
        write: function(newValue) {
            var current = target();
            if (current !== newValue){
                if (newValue.length >= minLength){
                    target(newValue);
                }
                else {
                    // forces textbox which is performing the write() to think
                    // the value has changed and reset itself.
                    target.notifySubscribers(current);
                }
            }
        }
    });

    //return the new computed observable
    return result;
};

你也不需要result(target());，因为它什么都不做。

【讨论】：