Re: re-jig two classes

Posted by Donald on March 31, 2007

In Reply to Re: re-jig two classes posted by Donald on March 31, 2007

: : : I have a zigzag line called TWire (TObject). To avoid the clickable area from being a surrounding rectangle for the whole zizgzag, which would overlap others, I created a second class TWseg (TGraphicControl). I have an array of 6 TWseg within TWire.
: : : The end result is that the clickable area is only as thick as the line and follows it's contour. Also, which is essential, I can detect a mouse click on any segment and know which.
: : : My problem is, when I click on a segment I cannot tell which wire it belongs to and am not too sure about the sender use.
: : -------------------

: : Add a property "Wire" to the TWSeg class, that gets/sets a pointer to the TWire that the TWSeg object belongs to. Example:

: : TWSeg = class(TGraphicControl)
: : private
: : ...
: : FWire: TWire; // added
: : ...
: : public
: : ...
: : property Wire: TWire read FWire write FWire; // added
: : ...

: : In your application, set the TWSeg.Wire property when you initialize the TWSeg objects, for example:

: : procedure TForm1....;
: : var Wire1: TWire;
: : ...
: : begin
: : Wire1 := TWire.Create;
: : ... initialize Wire1
: : ... finally, create its 6 segments:
: : for i := 1 to 6 do begin
: : Wire1.WSeg[i] := TWSeg.Create;
: : ...initialize the segment:
: : ...
: : // in this example: the same handler for mouse-down event
: : // of every segment (of course each segment could have it's own handler(s))
: : Wire1.WSeg[i].OnMouseDown := Form1.SegmentMouseDown;
: : // store a pointer to Wire1 in the segment:
: : Wire1.WSeg[i].Wire := Wire1;
: : end;
: : ...
: : end;

: : OnMouseDown is a property of TWSeg, and it's of the type TMouseEvent. So, write an event handler like this:

: : procedure TForm1.SegmentMouseDown(Sender: TObject; Button: TMouseButton;
: : Shift: TShiftState; X, Y: Integer);
: : var
: : Wire: TWire;
: : begin
: : ... do whatever you want to do when the mouse button goes down...
: : ...
: : Wire := (Sender as TWSeg).Wire;
: : ... use the wire-info, for example:
: : ShowMessage("Left of the wire: " + IntToStr(Wire.Left));
: : end;

: Thank you Willy for your time and effort. It is nice to have the full example and explanation.
: Your answer looks to be superb and I aim to try it today.
: If I have problems, which I don't foresee with your example, I hope I can come back to you.

Thank you again Willy, it works a treat.
I did make a variation. The Mousedown is within the TWseg and does not have a sender parameter, however, all I have to do is access wire, since I am already 'in' the segment. Perfect.