delphi pick a random value from an enum

Question

I need a delphi solution for this solution in java JAVA CODE

type
 TColors = (red, green, blue, white, purple, orange, yellow, black);
type
 TForm1 = class(TForm)
 Button1: TButton;
 Memo1: TMemo;
 procedure Button1Click(Sender: TObject);
 private
 { Private-Deklarationen }
 public
 { Public-Deklarationen }
 end;

 var Form1: TForm1;

 implementation

 {$R *.fmx}

 function RandomColor: TColors;
 begin
  result := blue;  //   make this random value from enum ????
end;

procedure TForm1.Button1Click(Sender: TObject);
var
s: string;
begin
  s := GetEnumName(TypeInfo(TColors), integer(RandomColor));
 Memo1.Lines.Add(s);   ///  print random color to memo 
end;

Chris Rolliston · Accepted Answer · 2013-10-12 08:52:26Z

5

function RandomColor: TColors;
begin
  Result := TColors(Random(Succ(Ord(High(TColors)))));
end;

var
  MyColor: TColors;
begin
  Randomize; //call this once at startup
  MyColor := RandomColor;

edited Oct 12, 2013 at 8:52

answered Oct 11, 2013 at 22:20

Chris Rolliston

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9 Comments

JensG Over a year ago

I would add a +1 to the Ord(), otherwise you will never see the highest possible enum value. The upper limit is exclusive.

Kromster Over a year ago

There seems to be a mistake. Random(A) returns range of 0..A-1, so if you want to have last element included you need to use Random(A+1).

Chris Rolliston Over a year ago

@JensG and Krom - completely right, thanks - I've now added a Succ call.

JensG Over a year ago

With the Succ() and RANGECHECKS ON my Delphi XE doesn't even compile this. Nice solution, indeed. BTW, why do you earn all the points while we do the work correcting your stuff?

Chris Rolliston Over a year ago

@JensG - the Succ call is against an integer, so works fine with range checking enabled - I have no idea why your Delphi XE 'doesn't even compile this'. Perhaps you haven't copied and pasted correctly?

|

JensG · Accepted Answer · 2013-10-12 11:43:26Z

0

Here's a complete test program, including a check against Low(TColors) not being zero, which must otherwise taken into account within the RandomColor function, if that later changes for some reason.

program Project7;

{$APPTYPE CONSOLE}
{$RANGECHECKS ON}

uses
  SysUtils;

type
  TColors = (red, green, blue);

const NAMES : array[TColors] of string = ('red','green','blue');

function RandomColor: TColors;
begin
  ASSERT( Ord(Low(TColors)) = 0);
  Result := TColors(Random(1+Ord(High(TColors))));
end;

var i : integer;
begin
  Randomize; 
  while true do begin
    for i := 0 to 7 do write('"', NAMES[RandomColor], '" ');
    writeln;
    writeln('press Ctrl+C to break, ENTER to continue ');
    readln;
  end;
end.

edited Oct 12, 2013 at 11:43

answered Oct 12, 2013 at 10:09

JensG

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