How do Hex editors display data so quickly?

Question

I'v created a Notepad-like application and if I load a 1MB file into the textbox, it takes about 1 minute. The Visual Studio Binary editor displays lines, Hex, and ascii versions in a fraction of a second. How do they get the data into the textbox so quickly? Thanks

Answer 1

They only read enough of the file to display what is viewable on screen. In other words, if your UI can only display 100 bytes at a time, you only need to read 100 bytes to fill the screen. If the user scrolls the window, you have to read additional bytes to fill in the missing pieces.