讲述如何开发一个控件,很有价值(七)

SUCCESS - (Nearly...)

I think you''''ll agree we are pretty close. There is just a little bit of flicker. This flicker is the SelStart jumping the Cursor position around the text. We need to hide this. This "Cursor" is also known as a Caret. Looking throught Win32.Hlp again we find the lovely, and appropriately named, HideCaret() function.

Lets try this then: everytime we change the value of MyRe.SelStart lets call HideCaret(MyRe.Handle) immediately before.

I''''ll be kind - that doesn''''t work. I tried 2 x HideCaret(MyRe.Handle), and it still didn''''t work. Neither did three,four or 25x. So close - but yet - so far. I think its time for another Delphi Rule:

DELPHI RULE #5 - If you bother to get your way through the atrocious index of the Win32.HLP file to find what you are looking for - make sure you really read what you found properly!

The key was the last paragraph in the description of not HideCaret but ShowCaret (which I had also read as I thought we were going to need it, especially to reverse my 25x HideCaret()). You also need another Delphi Rule to understand it:

DELPHI RULE #6 - Everything (basically) is a Window

You see the RichEdit is a windows control and is also.. in a weird sense.. a window. It has a Handle, which is why HideCaret would accept it. So re-reading the last line again we get:

So - in the end - we''''re back to were we started - we have to disable the RichEdit to stop the final bit of flickering. This also (co-incidentially) means that EM_HIDESELECTION is not needed anymore (if HideSelection is set properly during Design time). So in the end everyone gets 10/10 for marks!

ASH Version 0.9b