Delphi 对话框实现源码分析

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mob60475707384d 2013-12-27 10:17:00

文章标签 ico ide sed 2d 应用程序 文章分类 代码人生

Delphi 对话框实现源码分析

简介

在这篇文章中，我将大概的从Delphi XE2 的Dialogs单元入手，分析ShowMessage，MessageBox等对话框运行原理，希望能帮助你理解Delphi，不求你爱上她，只求让你能快速地解决问题。

跟踪代码

为了了解这些对话框的运行原理，我们需要跟踪进源代码中去，为此，你需要做如下设置

1. 简单创建一个使用了ShowMessage的VCL应用程序

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35	`unit``Unit1;``interface``uses``Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,``Dialogs, StdCtrls;``type``TForm1 =` `class``(TForm)``Edit1: TEdit;``Button1: TButton;``procedure``Button1Click(Sender: TObject);``private``{ Private declarations }``public``{ Public declarations }``end``;``var``Form1: TForm1;``implementation``{$R *.dfm}``procedure``TForm1``.``Button1Click(Sender: TObject);``begin``ShowMessage(Edit1``.``Text);``MessageBox(Self``.``Handle,``PChar``(Edit1``.``Text),``PChar``(Application``.``Title),``MB_ICONINFORMATION` `or``MB_OK);``MessageDlg(Edit1``.``Text,mtInformation,[mbOK,mbCancel],``0``);``end``;``end``.`

2. 在29行里设置一个断点, 再在Edit里输入一些内容,按下Message Box按钮, 按F7跟踪到Dialogs单元, 经过一段时间的仔细跟踪, 你会发现程序运行到下面一段代码:

1 2 3 4 5 6 7 8 9 10 11	`function``MessageDlgPosHelp(``const``Msg:` `string``; DlgType: TMsgDlgType;``Buttons: TMsgDlgButtons; HelpCtx:` `Longint``; X, Y:` `Integer``;``const``HelpFileName:` `string``):` `Integer``;``begin``if``(Win32MajorVersion >=` `6``)` `and``UseLatestCommonDialogs` `and``ThemeServices``.``ThemesEnabled` `then``Result := DoTaskMessageDlgPosHelp(``''``, Msg, DlgType, Buttons,``HelpCtx, X, Y, HelpFileName)``else``Result := DoMessageDlgPosHelp(CreateMessageDialog(Msg, DlgType, Buttons),``HelpCtx, X, Y, HelpFileName);``end``;`

函数MessageDlgPosHelp指出, 如果当前系统是Vista,sever2008或以上版本的系统,那就调用DoTaskMessageDlgPosHelp函数进行对话框显示, 否则调用DoMessageDlgPosHelp显示对话框. 继续跟踪DoTaskMessageDlgPosHelp函数, 你会发现如下一段代码:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136	`function``TCustomTaskDialog``.``DoExecute(ParentWnd: HWND):` `Boolean``;``const``CTaskDlgFlags:` `array``[TTaskDialogFlag]` `of``Cardinal``= (``TDF_Enable_Hyperlinks, TDF_Use_Hicon_Main,``tdf_Use_Hicon_Footer, TDF_ALLOW_DIALOG_CANCELLATION,``TDF_USE_COMMAND_LINKS, TDF_USE_COMMAND_LINKS_NO_ICON,``TDF_EXPAND_FOOTER_AREA, TDF_EXPANDED_BY_DEFAULT,``TDF_VERIFICATION_FLAG_CHECKED, TDF_SHOW_PROGRESS_BAR,``TDF_SHOW_MARQUEE_PROGRESS_BAR, TDF_CALLBACK_TIMER,``TDF_POSITION_RELATIVE_TO_WINDOW, TDF_RTL_LAYOUT,``TDF_NO_DEFAULT_RADIO_BUTTON, TDF_CAN_BE_MINIMIZED);``CTaskDlgCommonButtons:` `array``[TTaskDialogCommonButton]` `of``Cardinal``= (``TDCBF_OK_BUTTON, TDCBF_YES_BUTTON, TDCBF_NO_BUTTON,``TDCBF_CANCEL_BUTTON, TDCBF_RETRY_BUTTON, TDCBF_CLOSE_BUTTON);``CTaskDlgDefaultButtons:` `array``[TTaskDialogCommonButton]` `of``Integer``= (``IDOK, IDYES, IDNO, IDCANCEL, IDRETRY, IDCLOSE);``var``LWindowList: TTaskWindowList;``LModalResult:` `Integer``;``LRadioButton:` `Integer``;``LFlag: TTaskDialogFlag;``LFocusState: TFocusState;``LVerificationChecked: LongBool;``LTaskDialog: TTaskDialogConfig;``LCommonButton: TTaskDialogCommonButton;``begin``if``Win32MajorVersion <` `6``then``raise``EPlatformVersionException``.``CreateResFmt(``{$IFNDEF CLR}@{$ENDIF}``SWindowsVistaRequired, [ClassName]);``if``not``ThemeServices``.``ThemesEnabled` `then``raise``Exception``.``CreateResFmt(``{$IFNDEF CLR}@{$ENDIF}``SXPThemesRequired, [ClassName]);``{$IF NOT DEFINED(CLR)}``FillChar(LTaskDialog, SizeOf(LTaskDialog),` `0``);``{``$IFEND``}``with``LTaskDialog` `do``begin``// Set Size, Parent window, Flags``cbSize := SizeOf(LTaskDialog);``hwndParent := ParentWnd;``dwFlags :=` `0``;``for``LFlag := Low(TTaskDialogFlag)` `to``High(TTaskDialogFlag)` `do``if``LFlag` `in``FFlags` `then``dwFlags := dwFlags` `or``CTaskDlgFlags[LFlag];``// Set CommonButtons``dwCommonButtons :=` `0``;``for``LCommonButton := Low(TTaskDialogCommonButton)` `to``High(TTaskDialogCommonButton)` `do``if``LCommonButton` `in``FCommonButtons` `then``dwCommonButtons := dwCommonButtons` `or``CTaskDlgCommonButtons[LCommonButton];``// Set Content, MainInstruction, Title, MainIcon, DefaultButton``if``FText <>` `''``then``pszContent :=` `{$IFNDEF CLR}PWideChar{$ENDIF}``(``WideString``(FText));``if``FTitle <>` `''``then``pszMainInstruction :=` `{$IFNDEF CLR}PWideChar{$ENDIF}``(``WideString``(FTitle));``if``FCaption <>` `''``then``pszWindowTitle :=` `{$IFNDEF CLR}PWideChar{$ENDIF}``(``WideString``(FCaption));``if``tfUseHiconMain` `in``FFlags` `then``hMainIcon := FCustomMainIcon``.``Handle``else``begin``if``FMainIcon` `in``[tdiNone``..``tdiShield]` `then``pszMainIcon := LPCWSTR(CTaskDlgIcons[FMainIcon])``else``pszMainIcon := LPCWSTR(MakeIntResourceW(``Word``(FMainIcon)));``end``;``nDefaultButton := CTaskDlgDefaultButtons[FDefaultButton];``// Set Footer, FooterIcon``if``FFooterText <>` `''``then``pszFooter :=` `{$IFNDEF CLR}PWideChar{$ENDIF}``(``WideString``(FFooterText));``if``tfUseHiconFooter` `in``FFlags` `then``hFooterIcon := FCustomFooterIcon``.``Handle``else``begin``if``FFooterIcon` `in``[tdiNone``..``tdiShield]` `then``pszFooterIcon := LPCWSTR(CTaskDlgIcons[FFooterIcon])``else``pszFooterIcon := LPCWSTR(MakeIntResourceW(``Word``(FFooterIcon)));``end``;``// Set VerificationText, ExpandedInformation, CollapsedControlText``if``FVerificationText <>` `''``then``pszVerificationText :=` `{$IFNDEF CLR}PWideChar{$ENDIF}``(``WideString``(FVerificationText));``if``FExpandedText <>` `''``then``pszExpandedInformation :=` `{$IFNDEF CLR}PWideChar{$ENDIF}``(``WideString``(FExpandedText));``if``FExpandButtonCaption <>` `''``then``pszCollapsedControlText :=` `{$IFNDEF CLR}PWideChar{$ENDIF}``(``WideString``(FExpandButtonCaption));``// Set Buttons``cButtons := FButtons``.``Count;``if``cButtons >` `0``then``pButtons := FButtons``.``Buttons;``if``FButtons``.``DefaultButton <>` `nil``then``nDefaultButton := FButtons``.``DefaultButton``.``ModalResult;``// Set RadioButtons``cRadioButtons := FRadioButtons``.``Count;``if``cRadioButtons >` `0``then``pRadioButtons := FRadioButtons``.``Buttons;``if``not``(tfNoDefaultRadioButton` `in``FFlags)` `and``(FRadioButtons``.``DefaultButton <>` `nil``)` `then``nDefaultRadioButton := FRadioButtons``.``DefaultButton``.``ModalResult;``// Prepare callback``{$IF DEFINED(CLR)}``pfCallBack := @CallbackProc;``{``$ELSE``}``lpCallbackData := LONG_PTR(Self);``pfCallback := @TaskDialogCallbackProc;``{``$IFEND``}``end``;``LWindowList := DisableTaskWindows(ParentWnd);``LFocusState := SaveFocusState;``try``Result := TaskDialogIndirect(LTaskDialog,` `{$IFNDEF CLR}@{$ENDIF}``LModalResult,``{$IFNDEF CLR}@{$ENDIF}LRadioButton, {$IFNDEF CLR}@{$ENDIF}``LVerificationChecked) = S_OK;``FModalResult := LModalResult;``if``Result` `then``begin``FButton := TTaskDialogButtonItem(FButtons``.``FindButton(FModalResult));``FRadioButton := TTaskDialogRadioButtonItem(FRadioButtons``.``FindButton(LRadioButton));``if``LVerificationChecked` `then``Include(FFlags, tfVerificationFlagChecked)``else``Exclude(FFlags, tfVerificationFlagChecked);``end``;``finally``EnableTaskWindows(LWindowList);``SetActiveWindow(ParentWnd);``RestoreFocusState(LFocusState);``end``;``end``;`

上面这段代码在Dialogs单元的第5407行, 该函数先进行可用性判断, 然后填充

1	`LTaskDialog: TTaskDialogConfig;`

一个TTaskDialogConfig的结构体, 该结构体定义在CommCtrl单元第9550行, 其定义如下:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39	`type``{ $EXTERNALSYM TASKDIALOGCONFIG}``TASKDIALOGCONFIG =` `packed``record``cbSize: UINT;``hwndParent: HWND;``hInstance: HINST;` `// used for MAKEINTRESOURCE() strings``dwFlags: DWORD;` `// TASKDIALOG_FLAGS (TDF_XXX) flags``dwCommonButtons: DWORD;` `// TASKDIALOG_COMMON_BUTTON (TDCBF_XXX) flags``pszWindowTitle: LPCWSTR;` `// string or MAKEINTRESOURCE()``case``Integer``of``0``: (hMainIcon: HICON);``1``: (pszMainIcon: LPCWSTR;``pszMainInstruction: LPCWSTR;``pszContent: LPCWSTR;``cButtons: UINT;``pButtons: PTaskDialogButton;``nDefaultButton:` `Integer``;``cRadioButtons: UINT;``pRadioButtons: PTaskDialogButton;``nDefaultRadioButton:` `Integer``;``pszVerificationText: LPCWSTR;``pszExpandedInformation: LPCWSTR;``pszExpandedControlText: LPCWSTR;``pszCollapsedControlText: LPCWSTR;``case``Integer``of``0``: (hFooterIcon: HICON);``1``: (pszFooterIcon: LPCWSTR;``pszFooter: LPCWSTR;``pfCallback: TFTaskDialogCallback;``lpCallbackData: LONG_PTR;``cxWidth: UINT` `// width of the Task Dialog's client area in DLU's.``// If 0, Task Dialog will calculate the ideal width.``);``);``end``;``{$EXTERNALSYM _TASKDIALOGCONFIG}``_TASKDIALOGCONFIG = TASKDIALOGCONFIG;``PTaskDialogConfig = ^TTaskDialogConfig;``TTaskDialogConfig = TASKDIALOGCONFIG;`

该结构体其实是从MSDN里翻译过来的, 定义在CommCtrl.h 头文件里(需要Windows Vista, Windows Server 2008及以上版本, 我是用Windows 7 64位进行的测试), 详细说明可以查看MSDN.

TCustomTaskDialog.DoExecute 填充完LTaskDialog结构体后, 直接调用:

1 2	`Result := TaskDialogIndirect(LTaskDialog,` `{$IFNDEF CLR}@{$ENDIF}``LModalResult,``{$IFNDEF CLR}@{$ENDIF}LRadioButton, {$IFNDEF CLR}@{$ENDIF}``LVerificationChecked) = S_OK;`

TaskDialogIndirect显示对话框, TaskDialogIndirect定义在CommCtrl单元, 其代码如下:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30	`{ Task Dialog }``var``_TaskDialogIndirect:` `function``(``const``pTaskConfig: TTaskDialogConfig;``pnButton: PInteger; pnRadioButton: PInteger;``pfVerificationFlagChecked: PBOOL): HRESULT; stdcall;``_TaskDialog:` `function``(hwndParent: HWND; hInstance: HINST;``pszWindowTitle: LPCWSTR; pszMainInstruction: LPCWSTR; pszContent: LPCWSTR;``dwCommonButtons: DWORD; pszIcon: LPCWSTR; pnButton: PInteger): HRESULT; stdcall;``function``TaskDialogIndirect(``const``pTaskConfig: TTaskDialogConfig;``pnButton: PInteger; pnRadioButton: PInteger; pfVerificationFlagChecked: PBOOL): HRESULT;``begin``if``Assigned(_TaskDialogIndirect)` `then``Result := _TaskDialogIndirect(pTaskConfig, pnButton, pnRadioButton,``pfVerificationFlagChecked)``else``begin``InitComCtl;``Result := E_NOTIMPL;``if``ComCtl32DLL <>` `0``then``begin``@_TaskDialogIndirect := GetProcAddress(ComCtl32DLL,` `'TaskDialogIndirect'``);``if``Assigned(_TaskDialogIndirect)` `then``Result := _TaskDialogIndirect(pTaskConfig, pnButton, pnRadioButton,``pfVerificationFlagChecked)``end``;``end``;``end``;`

查看代码知道, TaskDialogIndirect 直接调用ComCtrl32.Dll里的函数:TaskDialogIndirect 显示对话框. 通过查询MSDN了解TaskDialogIndirect API的用途与用法:

The TaskDialogIndirect function creates, displays, and operates a task dialog. The task dialog contains application-defined icons, messages, title, verification check box, command links, push buttons, and radio buttons. This function can register a callback function to receive notification messages.

函数TaskDialogIndirect 用于创建, 显示, 运行一个任务对话框, 这个任务对话框可以包括由应用程序定义的图标,消息,标题,复选框,按钮,单选框. 该函数还可以接收一个回调函数用于接收通知信息

看到这里你或许会问:

如果我的系统是xp或其他低于Vista, server2008的系统呢? 由上文中可知, 如果是低版本的系统, 则调用DoMessageDlgPosHelp 函数进行对话框显示, 调用代码如下:

1 2	`Result := DoMessageDlgPosHelp(CreateMessageDialog(Msg, DlgType, Buttons),``HelpCtx, X, Y, HelpFileName);`

DoMessageDlgPosHelp代码:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15	`function``DoMessageDlgPosHelp(MessageDialog: TForm; HelpCtx:` `Longint``; X, Y:` `Integer``;``const``HelpFileName:` `string``):` `Integer``;``begin``with``MessageDialog` `do``try``HelpContext := HelpCtx;``HelpFile := HelpFileName;``if``X >=` `0``then``Left := X;``if``Y >=` `0``then``Top := Y;``if``(Y <` `0``)` `and``(X <` `0``)` `then``Position := poScreenCenter;``Result := ShowModal;``finally``Free;``end``;``end``;`

从DoMessageDlgPosHelp代码中可见, 该函数只是简单的将传递进来的TForm以模式窗口的形式显示在指定的位置.

下面是CreateMessageDialog代码:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157	`function``CreateMessageDialog(``const``Msg:` `string``; DlgType: TMsgDlgType;``Buttons: TMsgDlgButtons; DefaultButton: TMsgDlgBtn): TForm;``const``mcHorzMargin =` `8``;``mcVertMargin =` `8``;``mcHorzSpacing =` `10``;``mcVertSpacing =` `10``;``mcButtonWidth =` `50``;``mcButtonHeight =` `14``;``mcButtonSpacing =` `4``;``var``DialogUnits: TPoint;``HorzMargin, VertMargin, HorzSpacing, VertSpacing, ButtonWidth,``ButtonHeight, ButtonSpacing, ButtonCount, ButtonGroupWidth,``IconTextWidth, IconTextHeight, X, ALeft:` `Integer``;``B, CancelButton: TMsgDlgBtn;``{$IF DEFINED(CLR)}``IconID:` `Integer``;``{``$ELSE``}``IconID:` `PChar``;``{``$IFEND``}``TextRect: TRect;``LButton: TButton;``begin``Result := TMessageForm``.``CreateNew(Application);``with``Result` `do``begin``BiDiMode := Application``.``BiDiMode;``BorderStyle := bsDialog;``Canvas``.``Font := Font;``KeyPreview :=` `True``;``PopupMode := pmAuto;``Position := poDesigned;``OnKeyDown := TMessageForm(Result).CustomKeyDown;``DialogUnits := GetAveCharSize(Canvas);``HorzMargin := MulDiv(mcHorzMargin, DialogUnits``.``X,` `4``);``VertMargin := MulDiv(mcVertMargin, DialogUnits``.``Y,` `8``);``HorzSpacing := MulDiv(mcHorzSpacing, DialogUnits``.``X,` `4``);``VertSpacing := MulDiv(mcVertSpacing, DialogUnits``.``Y,` `8``);``ButtonWidth := MulDiv(mcButtonWidth, DialogUnits``.``X,` `4``);``for``B := Low(TMsgDlgBtn)` `to``High(TMsgDlgBtn)` `do``begin``if``B` `in``Buttons` `then``begin``if``ButtonWidths[B] =` `0``then``begin``TextRect := Rect(``0``,``0``,``0``,``0``);``Windows``.``DrawText( canvas``.``handle,``{$IF DEFINED(CLR)}``ButtonCaptions[B], -``1``,``{``$ELSE``}``PChar``(LoadResString(ButtonCaptions[B])), -``1``,``{``$IFEND``}``TextRect, DT_CALCRECT` `or``DT_LEFT` `or``DT_SINGLELINE` `or``DrawTextBiDiModeFlagsReadingOnly);``with``TextRect` `do``ButtonWidths[B] := Right - Left +` `8``;``end``;``if``ButtonWidths[B] > ButtonWidth` `then``ButtonWidth := ButtonWidths[B];``end``;``end``;``ButtonHeight := MulDiv(mcButtonHeight, DialogUnits``.``Y,` `8``);``ButtonSpacing := MulDiv(mcButtonSpacing, DialogUnits``.``X,` `4``);``SetRect(TextRect,` `0``,` `0``, Screen``.``Width` `div``2``,` `0``);``DrawText(Canvas``.``Handle, Msg, Length(Msg)+``1``, TextRect,``DT_EXPANDTABS` `or``DT_CALCRECT` `or``DT_WORDBREAK` `or``DrawTextBiDiModeFlagsReadingOnly);``IconID := IconIDs[DlgType];``IconTextWidth := TextRect``.``Right;``IconTextHeight := TextRect``.``Bottom;``{$IF DEFINED(CLR)}``if``DlgType <> mtCustom` `then``{``$ELSE``}``if``IconID <>` `nil``then``{``$IFEND``}``begin``Inc(IconTextWidth,` `32``+ HorzSpacing);``if``IconTextHeight <` `32``then``IconTextHeight :=` `32``;``end``;``ButtonCount :=` `0``;``for``B := Low(TMsgDlgBtn)` `to``High(TMsgDlgBtn)` `do``if``B` `in``Buttons` `then``Inc(ButtonCount);``ButtonGroupWidth :=` `0``;``if``ButtonCount <>` `0``then``ButtonGroupWidth := ButtonWidth * ButtonCount +``ButtonSpacing * (ButtonCount -` `1``);``ClientWidth := Max(IconTextWidth, ButtonGroupWidth) + HorzMargin ` `2``;``ClientHeight := IconTextHeight + ButtonHeight + VertSpacing +``VertMargin ` `2``;``Left := (Screen``.``Width` `div``2``) - (Width` `div``2``);``Top := (Screen``.``Height` `div``2``) - (Height` `div``2``);``if``DlgType <> mtCustom` `then``{$IF DEFINED(CLR)}``Caption := Captions[DlgType]` `else``Caption := Application``.``Title;``if``DlgType <> mtCustom` `then``{``$ELSE``}``Caption := LoadResString(Captions[DlgType])` `else``Caption := Application``.``Title;``if``IconID <>` `nil``then``{``$IFEND``}``with``TImage``.``Create(Result)` `do``begin``Name :=` `'Image'``;``Parent := Result;``Picture``.``Icon``.``Handle := LoadIcon(``0``, IconID);``SetBounds(HorzMargin, VertMargin,` `32``,` `32``);``end``;``TMessageForm(Result).Message := TLabel``.``Create(Result);``with``TMessageForm(Result).Message` `do``begin``Name :=` `'Message'``;``Parent := Result;``WordWrap :=` `True``;``Caption := Msg;``BoundsRect := TextRect;``BiDiMode := Result``.``BiDiMode;``ALeft := IconTextWidth - TextRect``.``Right + HorzMargin;``if``UseRightToLeftAlignment` `then``ALeft := Result``.``ClientWidth - ALeft - Width;``SetBounds(ALeft, VertMargin,``TextRect``.``Right, TextRect``.``Bottom);``end``;``if``mbCancel` `in``Buttons` `then``CancelButton := mbCancel` `else``if``mbNo` `in``Buttons` `then``CancelButton := mbNo` `else``CancelButton := mbOk;``X := (ClientWidth - ButtonGroupWidth)` `div``2``;``for``B := Low(TMsgDlgBtn)` `to``High(TMsgDlgBtn)` `do``if``B` `in``Buttons` `then``begin``LButton := TButton``.``Create(Result);``with``LButton` `do``begin``Name := ButtonNames[B];``Parent := Result;``{$IF DEFINED(CLR)}``Caption := ButtonCaptions[B];``{``$ELSE``}``Caption := LoadResString(ButtonCaptions[B]);``{``$IFEND``}``ModalResult := ModalResults[B];``if``B = DefaultButton` `then``begin``Default :=` `True``;``ActiveControl := LButton;``end``;``if``B = CancelButton` `then``Cancel :=` `True``;``SetBounds(X, IconTextHeight + VertMargin + VertSpacing,``ButtonWidth, ButtonHeight);``Inc(X, ButtonWidth + ButtonSpacing);``if``B = mbHelp` `then``OnClick := TMessageForm(Result).HelpButtonClick;``end``;``end``;``end``;``end``;`

由代码可见, CreateMessageDialog只是创建了一个TMessageForm, 然后动态地添加了一些设置. 写到这里或许可以解答一些人的问题: 对话框是不是一个窗口? 答案是:是.

你还可能会问: 为什么对话框可以停留在那一行代码直到用户操作完毕后再往下执行, 这里就需要了解一下模态窗口的知识: 请参见这篇文章 Delphi ShowModal解析

参考：

javascript:void(0)

简介