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讲述如何开发一个控件,很有价值(七)

来源：互联网 作者：西部数码 时间：2008-04-09

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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:

The caret is a shared resource; there is only one caret in the system. A window should show a caret only when the window has the keyboard focus or is active.

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:

The caret is a shared resource; there is only one caret in the system. A [RichEdit] should show a caret only when the [RichEdit] has the keyboard focus or is active.

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

procedure TForm1.RichEdit1Change(Sender: TObject);

var

SaveOnChangeIn: TNotifyEvent;
WasSelStart,WasRow,Row,BeginSelStart,EndSelStart: Integer;
MyRe : TRichEdit;
MyPBuff: array[0..255] of char;
MyTokenStr:string;
MyTokenState:TTokenState;
MyRun:PChar;
MySelStart: Integer;

begin

MyRe := TRichEdit(Sender);

SaveOnChangeIn := MyRe.OnChange;
MyRe.OnChange := nil;

MyRe.Enabled := False;

WasSelStart := MyRE.SelStart;
WasRow := MyRE.Perform(EM_LINEFROMCHAR, MyRE.SelStart, 0);
Row := WasRow;
BeginSelStart := MyRe.Perform(EM_LINEINDEX, Row, 0);
EndSelStart := BeginSelStart Length(MyRE.Lines.Strings[Row]);

StrPCopy(MyPBuff,MyRE.Lines.Strings[Row]);
MYPBuff[Length(MyRE.Lines.Strings[Row])] := #0;
MySelStart := BeginSelStart;
MyRun := MyPBuff;

while(MyRun^ <> #0) do
begin

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