warning of duplicate item while uploading file in document library

Question

I have a standard document library. I want to prompt the user if file name already exists in document library. I want this Friendly Error (with custom error text) on "Upload Document" form when when user clicks 'OK' button. I don't want to show default SharePoint Error page.

Answer 1

You can write a List Item Receiver (Synchronous).

More specific "Item Adding" event receiver, where you can get the current file name & check it against the existing items & show a message.

UPDATE:

public override void ItemAdding(SPItemEventProperties properties)
        {
            base.ItemAdding(properties);
            if (CheckIfExisting()) //this is where you call yout private method to check file names
            {
                try
                {
            properties.Cancel = true;
                    properties.ErrorMessage = "Please choose some other name.";
                }
                catch (InvalidCreatorIdException ex)
                {
                    properties.Cancel = true;
                    properties.ErrorMessage = ex.ToString();
                    properties.InvalidateListItem();
                    throw;
                }
            }
        }