The GridView 'gdABCD' fired event PageIndexChanging which wasn't handled.

1) If we change DataGrid to a GridView so inside any Event we change
DataGridPageChangedEventArgs to GridViewPageEventArgs.

2) If you set AllowPaging="true" or AllowSorting="true" on a GridView control without using a DataSourceControl DataSource (i.e. SqlDataSource, ObjectDataSource), you will run into the following errors: -

When changing the page on the GridView control: -

The GridView 'GridViewID' fired event PageIndexChanging which wasn't handled.
When clicking a column name to sort the column on the GridView control: -

The GridView 'GridViewID' fired event Sorting which wasn't handled.

As a result of not setting the DataSourceID property of the GridView to a DataSourceControl DataSource, you have to add event handlers for sorting and paging.