string String to return as the return value of the text property.
Callback, invoked when the text property is accessed.
The return value of this method will be returned as the value of the data property.
This method will be invoked on the main thread.
If not overridden, the default behavior of this callback is to call GetData. If GetData returns
null or an empty string, then this method will return
null or an empty string (respectively). Otherwise, this method will decode the byte array returned from GetData as a UTF8 string and return the decoded string.