ItemAdding

This rule is triggered when a new record is created, before it is added at the end of the data source.
This can be done :

• by a user clicking on an Add button.
• by code when calling AddNewAsync, AddAsync, InsertNewAsync or InsertAsync

It can be used, for example, to initialize the values of the newly created item.

Warning

When the rule is triggered, the item is not yet added to the view model datasource. Thus, modifying the value of its properties inside an ItemAdding rule does not trigger the associated PropertyChanged rules.

Warning

Adding an item does not persist it. The item is locally added to the datasource but is not sent to the server until saving.

See this article for more information on event rules execution order.

Arguments

The Arguments property provides the following options.

Name	Type	Description
Item	The type of the UI view model	Instance of the item being added to the datasource.
Cancel	bool	If set to true, the item will not be added to the datasource.
MarkAsVirtual	bool	If set to true, the item will be mark as virtual once the item has been added.

The MarkAsVirtual option is true when the item is being added via the add row of the datagrid, otherwise it is false.

Item versus DatasourceCurrent

Item refers to the item that has been added. It is the same as using Arguments.Item.

Important

In an ItemAdding event rule, since the item is not yet added to the datasource, DatasourceCurrent is always different from Item.

To know more on the difference between the Item and DatasourceCurrent properties in an UI view event rule, you can check this article.

Examples

Example 1
Initializing the OrderDate property with the current date.

Item.OrderDate = DateTime.Today;

Example 2
Initializing the OrderDate property with the date of the previously selected record.

if (DatasourceCurrent == null)
{
    // The datasource has no records, we initialize the date to the current date
    Item.OrderDate = DateTime.Today;
}
else
{
    // Initializing the date with the date of the previously selected record
    Item.OrderDate = DatasourceCurrent.OrderDate;
}