Chaining Knockout Custom Bindings

Question

I have a Knockout custom binding handler that I want to call the foreach bindings functionality on within it and then call a callback function afterwards. I keep getting a "Uncaught Error: You cannot apply bindings multiple times to the same element. " error now as I try to do this.

My custom binding is pretty simple (typescript):

/// <reference path="knockout.d.ts" />
ko.bindingHandlers["postForeach"] = {
    init: function (element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
        if (!allBindingsAccessor().postForeachCallback)
            throw "Callback not defined for postForeach binding!";

        //call foreach init functionality
        ko.bindingHandlers['foreach'].init(element, valueAccessor, allBindingsAccessor, viewModel, bindingContext);
    },
    update: function (element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
            //call foreach update functionality
            ko.bindingHandlers['foreach'].update(element, valueAccessor, allBindingsAccessor, viewModel, bindingContext);
            //call callback
            allBindingsAccessor().postForeachCallback();
    }
};

Is there something I am missing in constructing this?

Thanks!

EDIT:

Callback Function

self.populateMainContentWindow = function () {
                    var dataTable = $(this.tableId).dataTable();
        dataTable.fnDestroy();

                // create the datatable
                        var actualTable = this.jQuery(this.tableId);
        if (actualTable.length == 0) {
            return false;
        }

        // create the data table with options
        var newDataTable = actualTable.dataTable(this.options);

        // always set the width afterwards
        actualTable.css("width", "100%");
            };

Data Bind Signature (which is within a 'with' binding):

postForeach: array, postForeachCallback: $parent.viewModel().populateMainContentWindow

Answer 1

Knockout uses the return value of init to determine whether it should process the element's descendants. You can either just return the value of the foreach.init function or specifically return { controlsDescendantBindings: true } from your init function:

init: function (element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
    if (!allBindingsAccessor().postForeachCallback)
        throw "Callback not defined for postForeach binding!";

    //call foreach init functionality
    return ko.bindingHandlers['foreach'].init(element, valueAccessor, allBindingsAccessor, viewModel, bindingContext);
},

Reference: http://knockoutjs.com/documentation/custom-bindings-controlling-descendant-bindings.html