Binding context

In DotVVM, each HTML element or DotVVM control has the DataContext property. Using this property, you can change the context in which data bindings are evaluated.

Let's have the following view and viewmodel:

	@viewModel AddressViewModel, DotvvmDemo

	<div DataContext="{value: Customer}">
		{{value: Name}}
	</div>

public class AddressViewModel 
{
	public Customer Customer { get; set; }
}

public class Customer 
{
	public string Name { get; set; }
}

The DataContext property will make all bindings on the <div> element and its children to be evaluated in the context of the Customer property of the viewmodel.

If the DataContext binding is not present, the binding inside the <div> would have to be {{value: Customer.Name}}.

This mechanism allows you to simplify binding expressions - to use {value: Name} instead of {value: CustomerName}.

Scope variables

You can use the following binding context variables to navigate in the DataContext hierarchy:

• _root accesses the top-level viewmodel (the viewmodel of the page).
• _parent accesses the parent binding context.
• _parent2 accesses the parent's parent binding context, and so on...
• _this references the current context. It is useful when you need to pass the entire DataContext e.g. as an argument to a method.

For example, the following binding expression calls the DeleteAddress method in the page viewmodel and passes the current binding context as an argument:

<div DataContext="{value: Company}">
	<dot:Button Click="{command: _root.DeleteAddress(_this)}" />
</div>

public class EditCompanyViewModel 
{
	public Company Company { get; set; }

    public void DeleteAddress(Company company) 
    {
        // ...
    }
}

public class Company 
{
    public int Id { get; set; }
	public string Name { get; set; }
}

Collection context variable

If the binding context is a collection, you can use the _collection binding context variable to access the current item index and other properties. This behavior is most commonly used in the ItemTemplate of a Repeater, GridView, or similar data-bound controls.

The _collection variable has the following properties:

• _collection.Index
• _collection.IsFirst
• _collection.IsOdd
• _collection.IsEven

For example, you can print out the indexes of collection items:

<dot:Repeater DataSource="{value: Items}">
  <p>Item {{value: _collection.Index}}</p>
</dot:Repeater>

Null binding context behavior

There is one useful caveat to the DataContext property. If you set the DataContext of any element to null, the element will be removed from the DOM, and the bindings inside this element won't be evaluated at all.

After a non-null value is set to the DataContext property, the element will be returned back in the page DOM.

This can be used to create optional sections in the page which are available only when corresponding objects are loaded.

Access markup control properties

The _control binding context variable can be used in user control files (*.dotcontrol) to access properties of the user control.

See the Markup controls chapter for more info.

See also

• Value binding
• Resource binding
• Respond to user actions