Slow code insight - How to improve

Over the past couple of weeks I've noticed my code insight has gone slow. It seemed to happen after about 10 minutes of using Delphi, and got slower and slower to a point even typing in a string took over 5 seconds per character. The following reasons could have been the cause for this:

1. Something in Windows after an update is causing the issue. I believe this to be highly unlikely because all my other software works fine.
2. The problem seemed to coincide with installing the latest version of Visual Studio Professional (2015). This again seems unlikely.
3. Something specific to my current project is causing the problem. I think this is the most likely issue, other smaller projects work fine.

I did manage to improve the situation by turning off 'Error Insight' (red swiggle under error in code) in the code insight options. This feature was sometimes useful, but I also found it behaved strangely and reported errors in blank areas of code. I now have to restart Delphi every couple of hours instread of every 20 minutes.

I am still looking at how to improve the situation.

How to draw an arrow head

I've worked on a few developments that require graphical input form users like CAD, flow control and diagram applications. Here is a snippet of code that draws an arrow head to a line.

This is an example and in real code you might want to pass the arrow head length and width in as parameters.




procedure TMainForm.DrawArrowHead(const x1, y1, x2, y2: integer;
  Canvas: TCanvas);
var
  HeadLength : real;
  HeadWidth : real;
  xbase : Integer;
  xLineDelta : Integer;
  xLineUnitDelta : Double;
  xNormalDelta : Integer;
  xNormalUnitDelta : Double;
  ybase : Integer;
  yLineDelta : Integer;
  yLineUnitDelta : Double;
  yNormalDelta : Integer;
  yNormalUnitDelta : Double;
  OrigBrushColor : TColor;
begin
   OrigBrushColor := Canvas.Brush.Color;
   Canvas.Brush.Color := clBlack;
   xLineDelta := x2 - x1;
   yLineDelta := y2 - y1;
   xLineUnitDelta := xLineDelta / SQRT( SQR(xLineDelta) + SQR(yLineDelta));
   yLineUnitDelta := yLineDelta / SQRT( SQR(xLineDelta) + SQR(yLineDelta));
   // (xBase,yBase) is were the arrow line is perpendicular to base triangle.
   HeadLength := 12;
   HeadWidth := 2;
   xBase := x2 - ROUND(HeadLength * xLineUnitDelta);
   yBase := y2 - ROUND(HeadLength * yLineUnitDelta);

   xNormalDelta := yLineDelta;
   yNormalDelta := -xLineDelta;
   xNormalUnitDelta := xNormalDelta / SQRT( SQR(xNormalDelta) + SQR(yNormalDelta));
   yNormalUnitDelta := yNormalDelta / SQRT( SQR(xNormalDelta) + SQR(yNormalDelta));
   //Draw the arrow tip
   Canvas.Polygon([Point(x2,y2),
     Point(xBase + Round(HeadWidth*xNormalUnitDelta),
       yBase + ROUND(HeadWidth*yNormalUnitDelta)),
     Point(xBase - ROUND(HeadWidth*xNormalUnitDelta),
       yBase - ROUND(HeadWidth*yNormalUnitDelta)) ]);
   Canvas.Brush.Color := OrigBrushCOlor;
end;

TMemIniFile Vs TIniFile

Ini files have been around for some time now and are very useful for storing small amounts of data, and I use them as an alternative to the registry. Years ago I found that they had been designed with a limit of 64k, however these days it is possible to store more than that. Recently I needed to store a fair bit more than ini files are intended for and after some research decided the way to use them.

There are 2 main classes for reading and writing to ini files TIniFile and TMemIniFile, but which one should you use?

Basically, I found out that TIniFile should be used to write to the file and TMemIniFile should be used to read from the file. A few people mentioned to me to just use the TMemIniFile and you should not use TIniFile, however I believe the TMemIniFile uses an internal hash table which causes writing to the file to be slow. So there it is, use TIniFile to write and TMemIniFile to read.

Delphi increases in popularity

I've been developing software using Delphi for well over 15 years and for at least the last 10 years I hear all about how Delphi is dead and developers are moving to other languages. I have just looked at the TOIBE index which list software development languages by popularity and Delphi has moved from ranking 15 last year to 13 this year, so this shows that Delphi is going to stay around for some time to come.

Obviously these ranking change constantly and it could be next year Delphi goes back down the list, but I do think it says shows that Delphi is not dead and that all the people who have said 'Delphi is dead' for the last 10+ years are wrong.

Prefix class with 'I'

The other week I was looking at some code another Delphi developer had written and noticed that he prefixed classes with 'I' instead of 'T'. In my world the prefix 'I' means its an interface, but he argued that an abstract class is an interface and that all abstract classes should be prefixed with 'I'. I disagreed with him for various reasons, one being that Delphi standard classes do not do this.

Does anyone else prefix their abstract classes with 'I' and only use 'T' for concrete classes?  

How to refresh a treeview control

I recent development I have been working on uses a TTreeview control. The underlining classes that relate to the nodes of the control get updated and I reflect the state of the class as dynamic colour of the node text. This state change can happen every few seconds so I wanted to refresh the treeview at least every couple of seconds.

I read a few articles on how to do this but found the treeview would flicker. The best solution I found was simple, when I wanted to refresh just simply call the 'invalidiate' method, at first this did not work until I set the doublebuffered property to true and now it works really well.

Delphi XE5 App does not work with Android Lollipop

Last year I developed a prototype App using Delphi XE5 and deploying to my Nexus 4. It all worked OK and I was fairly happy with what I had. Last month I updated my Nexus phone to Android Lollipop, the other day I tried to open the App and nothing happened it just did not work anymore. I was a little disappointed and a similar App I had developed using Xamarin still worked fine. I am now not sure how feasible it is using Delphi to develop Android Apps.