Skip to main content

Creating Custom binding handler in knockout and how it works

Custom helper is very useful in knockout it is suggested to make custom helpers for implementing any custom knockout functionality and sometime it is required to do so like when you are using templates in knockout as we know templates render later than jquery code after knockout apply binding call. So with the common jquery code we can’t access the element which declares inside the templates.

For that we need to create custom knockout handler which executes at the time when element renders, so we can access the element and child element inside custom handler.

Below is the prototype for custom handler:
ko.bindingHandlers.slickgrid = {
init: function(element, valueAccessor, allBindingAccessor, viewModel, bindingContext) {
    var settings = valueAccessor();

    var gridData = ko.toJS(;
    var columns = ko.utils.unwrapObservable(settings.columns);
    var options = ko.unwrap(settings.options);

    var grid = new Slick.Grid(element, gridData, columns, options);

    $(element).data('grid', grid);
update:function(element, valueAccessor, allBindingAccessor, viewModel, bindingContext) {
    var grid = $(element).data("grid");

    var settings = valueAccessor();
    var gridData = ko.toJS(;
    grid.setData(gridData, false);



<div data-bind="uniqueName:true, slickGrid: { columns: $root.columns, data: $root.Data , options:$root.viewOptions }" class="size100"></div>

There are 5 parameters -

Element: the element in which custom binding handler attached.

valueAccessor: property that you pass in handler during the call.

allBindingAccessor: all binding handlers that attached with the element.
all binding accessor for knockout custom handler
viewModel: the viewmodel with that you applied binding in case of template data that is binding with template will be the viewmodel.

bindingContext: binding context like $data, $parentdata, how many parent data is there etc.

binding context for knockout custom handler

How custom handler works and update fires:

First time when custom handler execute both function fires Knockout execute the code of Init() as well as the code of Update() and analysis the dependencies declared in Update function.

And when these dependencies change knockout executes the code of Update() function again, like in above example if valueAccessor().data (gridData) dependency changes then Update() will fire.

Popular posts from this blog

Uploading large file in chunks in Mvc c# from Javascript ajax

Often we have a requirement to upload files in, Mvc c# application but when it comes to uploading larger file, we always think how to do it as uploading large file in one go have many challenges like UI responsiveness, If network fluctuate for a moment in between then uploading task get breaks and user have to upload it again etc.

Regular expression for alphanumeric with space in c#

How to validate that string contains only alphanumeric value with some spacial character and with whitespace and how to validate that user can only input alphanumeric with given special character or space in a textbox (like name fields or remarks fields). In remarks fields we don't want that user can enter anything, user can only able to enter alphanumeric with white space and some spacial character like -,. etc if you allow. Some of regular expression given below for validating alphanumeric value only, alphanumeric with whitspace only and alphanumeric with whitespace and some special characters.

How to handle click event of linkbutton inside gridview

Recently I have posted how to sort only current page of gridview , Scrollble gridview with fixed header through javascript , File upload control inside gridview during postback and now i am going to explain how to handle click event of linkbutton or any button type control inside gridview. We can handle click event of any button type control inside gridview by two way first is through event bubbling and second one is directly (in this type of event handling we need to access current girdviewrow container)

regex - check if a string contains only alphabets c#

How to validate that input string contains only alphabets, validating that textbox contains only alphabets (letter), so here is some of the ways for doing such task. char have a property named isLetter which is for checking if character is a letter or not, or you can check by the regular expression  or you can validate your textbox through regular expression validator in Following code demonstrating the various ways of implementation.