Delphi - 是否可以禁用 Delphi 的表单延迟加载？

Question

我听说 Delphi 应用程序使用“延迟加载”，延迟加载表单组件，直到它们被实际引用。 another post 中提到过- “这就是我们将 TPageControl 更改为延迟加载的原因 - Delphi IDE 的选项对话框加载时间过长!”

我假设这也适用于使用 Delphi 创建的应用程序，但我在 VCL 源代码中找不到任何提及延迟加载的内容，这表明如果它确实存在，它可能被称为其他东西。

在正常使用中，应用程序不经常启动并运行很长时间的情况下，可能需要放弃更快的启动时间并在第一次实际使用 VCL 组件时更快地绘制 VCL 组件。

Delphi 程序员对此有任何控制权吗？ (LazyLoad := false ; 没用 ;-)

Answer 1

考虑以下简单的演示项目:

项目1.dpr

program Project1;

uses
  Vcl.Forms,
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

Unit1.pas

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes,
  Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ComCtrls, Vcl.StdCtrls;

type
  TButton = class(Vcl.StdCtrls.TButton)
  protected
    procedure CreateWnd; override;
  end;

  TForm1 = class(TForm)
    PageControl1: TPageControl;
    TabSheet1: TTabSheet;
    TabSheet2: TTabSheet;
    TabSheet3: TTabSheet;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure FormCreate(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TButton.CreateWnd;
begin
  inherited;
  Writeln('Window created: ' + Name);
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  i: Integer;
begin
  AllocConsole;
end;

end.

Unit1.dfm

object Form1: TForm1
  Caption = 'Form1'
  ClientHeight = 299
  ClientWidth = 635
  OnCreate = FormCreate
  PixelsPerInch = 96
  TextHeight = 13
  object PageControl1: TPageControl
    Left = 40
    Top = 40
    Width = 537
    Height = 233
    ActivePage = TabSheet1
    object TabSheet1: TTabSheet
      Caption = 'TabSheet1'
      object Button1: TButton
        Caption = 'Button1'
      end
    end
    object TabSheet2: TTabSheet
      Caption = 'TabSheet2'
      object Button2: TButton
        Caption = 'Button2'
      end
    end
    object TabSheet3: TTabSheet
      Caption = 'TabSheet3'
      object Button3: TButton
        Caption = 'Button3'
      end
    end
  end
end

当你运行它时，控制台窗口会显示:

Window created: Button1

As you select each page in turn, the other buttons are created, as shown in the console window:

Window created: Button1Window created: Button2Window created: Button3

Now change the OnCreate event handler to force each page to be visible when the form is created:

procedure TForm1.FormCreate(Sender: TObject);
var
  i: Integer;
begin
  AllocConsole;

  for i := 0 to PageControl1.PageCount-1 do begin
    PageControl1.Pages[i].Visible := True;
  end;
end;

现在，当表单首次显示时，控制台窗口显示:

Window created: Button1Window created: Button2Window created: Button3

This is because, as Danny says, the windows are not created until they are shown.

Now, the nuance with regards page controls is the handling of visibility of the pages. The constructor of TTabSheet contains this:

Visible := False;

此外， Visible TTabSheet 的属性(property)是这样发布的:

property Visible stored False;

这意味着当一个页面控件开始它的生命时，它的页面是隐藏的，在 VCL 意义上有 Visible。等于 False .正如 Danny 所说，窗口控件是在显示控件时首先创建的。这发生在 TWinControl.UpdateShowing开始是这样的:

procedure TWinControl.UpdateShowing;
var
  ShowControl: Boolean;
  I: Integer;
begin
  ShowControl := (FVisible and (not (csDesigning in ComponentState) or not (csDesignerHide in ControlState)) or
    ((csDesigning in ComponentState) and not (csDesignerHide in ControlState)) and
    not (csNoDesignVisible in ControlStyle)) and
    not (csReadingState in ControlState) and not (csDestroying in ComponentState);
  if ShowControl then
  begin
    if WindowHandle = 0 then CreateHandle; // <-- this is the key
    if FWinControls <> nil then
      for I := 0 to FWinControls.Count - 1 do
        TWinControl(FWinControls[I]).UpdateShowing;
  end;
  ....
end;

页面开始时不显示，然后当它们在 TPageControl.ChangeActivePage 中变为事件状态时对新激活的页面执行以下操作:

Page.BringToFront;
Page.Visible := True;

设置 Visible至 True结果 TWinControl.UpdateShowing执行，并创建窗口句柄。

这就是为什么在表单创建时使所有页面可见的上述技巧具有您想要的效果。

现在，以上所有内容都非常以页面控制为中心。对于许多其他控件，如果控件可见，则在创建窗体时首先创建窗口。如果您对特定表格有特定问题，那么最好分享具体细节。