# OnCalendarViewChanging

The **OnCalendarViewChanging** client-side event handler of the [ASP NET AJAX Calendar](https://www.telerik.com/products/aspnet-ajax/calendar.aspx) is called when the calendar navigates to a new view, before the viewable area rendered by the calendar is changed.

The event handler receives two arguments:

1. the [RadCalendar object](https://www.telerik.com/products/aspnet-ajax/documentation/controls/calendar/client-side-programming/radcalendar-object) that fired the event.

2. an event arguments object that exposes the following methods:OnCalendarViewChanging event arguments object

| Name                  | Return Type | Arguments | Description                                                           |
| --------------------- | ----------- | --------- | --------------------------------------------------------------------- |
| **get_step()**        | int         |           | Returns the number of views by which the calendar is about to change. |
| **set_cancel(value)** |             | bool      | Lets you prevent the view from changing.                              |

This event can be used to pre-process some conditions or visual styles and content before the final rendering of the calendar. The following example uses the **OnCalendarViewChanging** event to prevent the view from changing unless a date in the current month is selected:

```ASPNET
<telerik:RadCalendar RenderMode="Lightweight" ID="RadCalendar1" runat="server" ShowOtherMonthsDays="False" >
	<ClientEvents OnCalendarViewChanging="checkSelections" />
</telerik:RadCalendar>
```

```JavaScript
function checkSelections(sender, eventArgs) {
    var selDates = sender.get_selectedDates();
    var focus = sender.get_focusedDate();
    var viewHasSelection = false;
	
    for (var i = 0; i < selDates.length; i++) {
        if ((selDates[i][0] == focus[0]) && (selDates[i][1] == focus[1])) {
			viewHasSelection = true;
		}
    }
	
    eventArgs.set_cancel(!viewHasSelection);
	
    if (eventArgs.get_cancel()) {
    	alert("You must select a value before moving " + (eventArgs.get_step() > 0 ? "forward " : "back ") + "to another month.");
	}
}
```

## See Also

* [OnCalendarViewChanged](https://www.telerik.com/products/aspnet-ajax/documentation/controls/calendar/client-side-programming/events/oncalendarviewchanged)

* [DefaultViewChanged](https://www.telerik.com/products/aspnet-ajax/documentation/controls/calendar/server-side-programming/events/defaultviewchanged)