Trouble with Knockout.js binding not refreshing

I have encountered an issue with my view model where the bindings work correctly when adding objects to the observable array, but do not update when clearing the array.

To help illustrate the problem, I have created a jsfiddle and I am seeking guidance on how to resolve it:

http://jsfiddle.net/chriswnichols/gcywcce7/

function County(name) {
    this.Name = name;
}

function ListCriteria() {
    var self = this;
    self.States = ko.observableArray([]);
    self.Counties = ko.observableArray([]);
    self.Zips = ko.observableArray([]);
    self.Cities = ko.observableArray([]);
    self.DobRanges = ko.observableArray([]);
    self.Clear = function () {
        self.States = ko.observableArray([]);
        self.Counties = ko.observableArray([]);
        self.Zips = ko.observableArray([]);
        self.Cities = ko.observableArray([]);
        self.DobRanges = ko.observableArray([]);
    };
}

var ViewModel = function () {
    var listCriteria = new ListCriteria(),
        reset = ko.computed(function () {
            listCriteria.Clear();
        });
    return {
        listCriteria: listCriteria,
        reset: reset
    }
};
viewModel = new ViewModel();
ko.applyBindings(viewModel);

Any assistance in resolving this issue would be greatly appreciated. Thank you.

Answer №1

The issue arises because each time a new observable array is created, causing the old ones to remain bound in KnockoutJS. This results in the new (unbound) arrays not affecting the user interface.

A possible solution is to clear out the original observable arrays using the ObservableArray.removeAll method:

self.Clear = function () {
    [self.States, self.Counties, self.Zips].forEach(function (arr) {
        arr.removeAll();
        // An alternative is to simply update the existing observable with an empty array
        // arr([]);
    });
};

Another approach involves utilizing an observable indirection layer and rebinding the outer observable, though this may not be necessary in this scenario. Here's how it could be implemented:

var ViewModel = function () {
    var listObs = ko.observable(new ListCriteria());
    return {
        listCriteria: listObs,
        reset: function () {
            listObs( new ListCriteria() );
        }
    }
}

To utilize this setup, you can bind it as foreach: listCriteria().Counties. The same concept can be applied to individual arrays within the object like foreach: listCriteria.States(), but it seems unnecessary given that they are already observable arrays.

function ListCriteria() {
    var self = this;
     self.States = ko.observable(ko.observableArray([]));
     self.Clear = function () {
         self.States(ko.observableArray([]));
     };
}

Ultimately, the key to resolving this issue lies in only making changes to observable objects to impact the bound data.

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