表单显示上的 Delphi 访问冲突

Question

Sorry for having to open new question but I can't find an answer anywhere.

My app is still in progress, but basically I'm trying to call another Form from my MainForm when initializing players, however I get an Access Violation error. Would you please explain to me why this could be happening?

My MainForm code:

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Buttons, ExtCtrls, jpeg, pngimage, getPlayer_u;...

procedure TfrmMain.FormCreate(Sender: TObject);
begin
  Randomize;

  InitGameSetup();
end;...

procedure TfrmMain.InitGameSetup();
begin
  SetWindowProperties();
  InitBackGround();
  InitMainMenu();
  InitGameBoard();
  InitScrabbleTileRack();
  InitPlayers();
//  GameLoop();
end; ...

procedure TfrmMain.InitPlayers();
var
  I : Integer;
  sName, sSurname : string;
begin
  setLength(Players, NUMBER_OF_PLAYERS);
  for I := 1 to High(Players) do
    begin
      GetPlayer(); ---------------- problem is here
      with Players[I] do
        begin
          Name := sName;
          Surname := sSurname;
        end;
    end;
end;...

procedure TfrmMain.GetPlayer();
begin
  frmGetPlayer.Show;
end;

My frmGetPlayer :

unit getPlayer_u;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TfrmGetPlayer = class(TForm)
    btnSubmit: TButton;
    edtName: TEdit;
    edtSurname: TEdit;
    procedure FormCreate(Sender: TObject);
    procedure btnSubmitClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    sPlayerName, sPlayerSurname : string;
  end;

var
  frmGetPlayer: TfrmGetPlayer;

implementation

{$R *.dfm}

procedure TfrmGetPlayer.btnSubmitClick(Sender: TObject);
begin
  sPlayerName := edtName.Text;
  sPlayerSurname := edtSurname.Text;

  if not ((Length(sPlayerName) >= 1) and (Length(sPlayerSurname) >= 1)) then
    MessageDlg('Please enter a name and surname.', mtInformation, [mbOK], 0)
  else
    Self.Free;
end;

procedure TfrmGetPlayer.FormCreate(Sender: TObject);
begin
  with Self do
    begin
      Position := poScreenCenter;
      BorderStyle := bsDialog;
    end;
end;

end.

My dpr:

program main_p;

uses
  Forms,
  main_u in 'main_u.pas' {frmMain},
  getPlayer_u in 'getPlayer_u.pas' {frmGetPlayer};

{$R *.res}

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TfrmMain, frmMain);
  Application.Run;
end.

The error:

Answer 1

Only your MainForm object is created automatically at program startup. Inside its OnCreate event, your Player Form object hasn't been created yet, so the frmGetPlayer variable is not pointing at a valid object.

frmGetPlayer is a global variable, so it is initially nil . The error message is telling you that you are accessing invalid memory near address 0, which is almost always an indication of accessing a member of a class via a nil pointer.

So, you can't call frmGetPlayer.Show() until after you have created the Player Form object and assigned frmGetPlayer to point at it. Which the code you showed is not doing.