onUpload

Single-file callback that fires the moment a user adds a file to the Upload control queue (drag & drop or picker). Returning false from the event handler cancels the upload for that specific entry.

When it runs

• After the client-side threshold checks (extension, blacklist, size, max files) succeed.

• Before the binary is sent to Attachment/Upload and before the document type is set or the record is linked.

Use it to enforce additional validation (record must exists, document type semantics, advanced MIME checks) or to tweak the upload metadata (file name template, doc type override) right on the client.

Event payload (eventArgs.details)

Field	Description
fileName	Final name after applying the optional template (can still be changed in the handler).
originalFileName	Name reported by the browser/OS.
fileSize	Size in bytes.
fileType	MIME type reported by the browser.
documentTypeId / documentTypeLabel	Selected document type or null if none was chosen.
recordId / appName	Record context that the Upload control plans to use for auto-linking. Empty when the form has not been saved yet.
rawFile	Native File object reference for deep inspection.

Example

if (!checksSuccessfull) {
    return false; //this will stop the upload
} else {
    return true; //this will allow the upload to continue
}

Tips

• Always guard against missing record context (brixxApi.attachmentRecordId) when uploads must be linked immediately.

• Heavy logic or server calls should remain rare; running them per file impacts perceived performance.