Mastering Delphi Programming: A Complete Reference Guide

Updating a progress bar

Almost any change to VCL controls can cause one or more Windows messages to be sent to the operating system. That takes time, especially as the program waits for the operating system to process the message and return an answer. This can happen even if nothing has changed in the user interface.

The next demonstration will show how an abundance of messages can slow down the execution speed. I must admit that the code in the ProgressBar demo is a bit contrived. Still, I assure you that I have seen a similar code running in production.

This demo simulates reading a large file block by block. (The code doesn't really open and read the file; it just runs a loop which would do the reading.) For each read block, a progress ...