Question

For example i have such template and i want to calculate some values dynamically based on current $index

    <div class="cond" title="Click to flip">
        <div class="condFlip" data-bind="attr: {id: Id }, click: viewModel.setClick">               
            <div class="piece-all piece" data-bind="attr: {style: background-position: viewModel.getValue($index)  viewModel.getValue($index) }"></div>
        </div>
    </div>      
</script>

<script type="text/javascript">
    viewModel = {
        flips: ko.observableArray([]),      

        setClick: function (data, e) {
            e.preventDefault();
            //doing things
        },

        getValue: function (data, e) {
            return //get my value
        }        
    };    

ko.applyBindings(viewModel);

so how can i use function viewModel.getValue in model binding? is there any way of doing this?

Answer 1

You can call functions that return strings in the way that you are doing it, but your format is slightly off. Here are a few tips:

• you can use the style binding rather than the attr binding, as it will add/remove the individual styling rather than replace the entire style attribute (maybe not important for your case).

• in the binding string, background-position is an invalid property name in the object literal that you are creating to specify your bindings. You need to either use "background-position" in quotes or the name that you can use in JavaScript backgroundPosition

• you would either want your getValue function to return the full string like 15px 30px or build it in the binding like: getValue($index) + ' ' + getValue($index)

• $index is an observable, so you will need to call it as a function to get its value, when you are processing it in your function.

So, your binding might look like:

<i class="icon-blah" data-bind="style: { backgroundPosition: viewModel.getValue($index) + ' ' + viewModel.getValue($index) }"></i>

Sample here: http://jsfiddle.net/rniemeyer/BAVZa/