避免使用ko.compute主动聆听

Question

how can i avoid height [ ko.computed] repeatedly run when i put a mouse over ? [ mouseAreHoverFotoBanner ]

When a read something from ui, all ko.computed are automatically executed...

Code sample [ js ]:

var ui = function () {

            var fotoBanner = {
                scale: scale,
                scaleIn: function () { scale(0.9); },
                scaleOut: function () { scale(scale(0)); },
                mouseAreHoverFotoBanner: mouseAreHoverFotoBanner,
                enableHoverFotoBanner: function () { ( (mouseAreHoverFotoBanner()) ? "" :mouseAreHoverFotoBanner(true)); },
                disabelHoverFotoBanner: function () { mouseAreHoverFotoBanner(false); },

                url: ko.observable("270829_184226781631642_1559736_n.jpg"),
                height: ko.computed(function () {
                    toastr.info((this.wd.height() * scale()) + "px");//debug
                    return (this.wd.height() * scale()) + "px";
                }, this)
            };

            return { fotoBanner: fotoBanner };
        };

Answer 1

A computed will always automatically update, because it is a Knockout observable . To maintain full control of updating: you may use a normal JavaScript variable, calculated from the Knockout observables wd.height() and scale() . As a normal JavaScript variable, your new variable (say, " height ") can be updated only at the times you wish for it to update.

• For example:

  var height = (this.wd.height() * scale()) + "px"; var updateHeight = function () {

  }

Ways to update:

• Write a setTimeout() to update it after an amount of time you choose. This can be put in a while loop for repeated updating at an interval you choose.

• Write an update function (say, updateHeight() ) and call it every time height() or scale() changes. This can be done by placing a subscribe() on height() and scale() :

   wd.height.subscribe(function(newValue) { updateHeight(); });