Here's a "writableComputedArray" if you want the best of both worlds. If you add/remove from the array, and a subsequent re-compute of the observable performs the same add/remove, subscribers will not get notified the second time. However, it's your responsibility to make sure that there are no discrepancies between the computation of the array and what actually gets added/removed. You can accomplish this by making the necessary changes in the sortable binding's afterMove event.
ko.writeableComputedArray = function (evaluatorFunction) {
// We use this to get notified when the evaluator function recalculates the array.
var computed = ko.computed(evaluatorFunction);
// This is what gets returned to the caller and they can subscribe to
var observableArray = ko.observableArray(computed());
// When the computed changes, make the same changes to the observable array.
computed.subscribe(function (newArray) {
// Add any new values
newArray.forEach(function (value) {
var i = observableArray.indexOf(value);
if (i == -1) {
// It's a new value, push it
observableArray.unshift(value);
}
});
// Remove any old ones. Loop backwards since we're removing items from it.
for (var valueIndex = observableArray().length - 1; valueIndex >= 0; valueIndex--) {
var value = observableArray()[valueIndex];
var i = newArray.indexOf(value);
if (i == -1) {
// It's an old value, remove it
observableArray.remove(value);
}
}
});
return observableArray;
};