This example showcases a few scenarios of adding validation to the listview Edit and Insert operations.

The general way to do that is to:

1. Add the desired validation (forms, some async logic from a data service, whatever suits the project needs).
2. Cancel the ListView event when validation fails (set the IsCancelled flag of the event arguments to true) to keep it in edit/insert mode.

In this sample project, you will find the following examples:

• synchronous validation - one way to add an EditForm and instantiate an EditContext to use for validation

• async methods - one way to use the edit form (or other remote validation) when the methods are async.

• custom edit form - an example of implementing all the editing/inserting logic with your own code without having to take into account any built-in ListView logic and capabilities - this provides you with full control over the rendering, logic, async operations and so on.

You may also find useful articles like the following ones on handling server-side validation:

• MSDN: Handle WebAPI Errors

• MSDN: Blazor Server Validation

• Handling Errors in ASP.NET Core WebAPI by devtrends.co.uk