Binding Syntax

One of the most useful things in DotVVM is the data binding. The magic of writing "rich client-side apps" without using JavaScript is the ability of DotVVM to translate binding expressions to JavaScript.

All data bindings are strongly typed and compiled right before the page is accessed for the first time. Dynamic types are not supported yet.

Therefore, each master page has to specify the @viewModel directive so the binding compiler can verify the correctness of the expression and compile it.

There are several types of data binding in DotVVM.

• {value: Property} - accesses the value of a specified property from the viewmodel.
• {command: Function()} - executes the specified method in the viewmodel.
• {staticCommand: Function()} - executes a static method in the viewmodel.
• {resource: ResourceFile.ResourceKey} - gets the resource entry value from the specified RESX file.

There are also the controlCommand and controlProperty bindings. They are used when writing your own user controls. You can find more about them in the Markup Controls section.

The commercial version of DotVVM for Visual Studio shows the IntelliSense for expressions in all types of bindings.

Usage

We can use a data binding expression almost everywhere in DOTHTML.

The binding expression is enclosed in curly braces and has two parts:

• Binding type - e.g. value, command etc.
• Binding expression - a C#-like expression (with some restrictions and some enhancements).

For example, to bind some value from the viewmodel to a HTML attribute, you can use this syntax:

<a href="{value: Url}">...</a>

If you want to render the value as a text, you have to use double curly braces. That is because of the <script> and <style> elements. The curly braces have special meaning inside these elements.

<p>Hello {{value: YourName}}!</p>

It is not possible to use the binding expression in the HTML attribute value in combination with another content:

<!-- This does not work - the whole attribute value has to be a data binding! -->
<a class="tab {value: AdditionalLinkClass}">...</a>

However, you can use expressions inside the binding, so you can combine the values easily:

<!-- This works - the whole attribute is a data binding! -->
<a class="{value: "tab " + AdditionalLinkClass}">...</a>