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<HTML><LINK HREF="style.css" REL="STYLESHEET" TYPE="text/css"><HEAD><TITLE>Tutorial: Dialogs, GUI coders best friend</TITLE></HEAD><BODY><FONT SIZE="-1">[ <A HREF="./index.html">contents</A>| <A HREF="http://www.winprog.org/">#winprog</A>]</FONT><HR><H1>Dialogs, GUI coders best friend</H1><P>Example: dlg_one</P><IMG SRC="images/dlg_one.gif" ALT="[images/dlg_one.gif]" ALIGN="right">There's hardly a windows program out there that doesn't use dialog boxes. Justgo File -> Open in any text editor or any other kind of editor for that matterand voila, you are presented with a dialog box, one that probably allows youto select a file to be opened.<P>Dialogs aren't limited to the standard open file ones, they can look like anddo whatever you choose. The attractive point of dialogs is that they providea quick way to arrange and create a GUI (Graphic User Interface) and evensome default processing, cutting down on the amount of code you must write.<P>One thing to remember is that <B>dialogs are just windows</B>. The difference betweena dialog and a "normal" window is that the system does some additional defaultprocessing for dialogs, such as creating and initialising controls, and handling tab order. Nearly all APIs that are applicable to "normal" windows will work just as wellon dialogs, and vice versa!<P>The first step is to create the dialog resource. As with any resource how youdo this will depend on your compiler/IDE. Here I will show you the plain textof the dilaog in the .rc file and let you incorporate it into your project.<PRE CLASS="SNIP">IDD_ABOUT DIALOG DISCARDABLE 0, 0, 239, 66STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENUCAPTION "My About Box"FONT 8, "MS Sans Serif"BEGIN DEFPUSHBUTTON "&OK",IDOK,174,18,50,14 PUSHBUTTON "&Cancel",IDCANCEL,174,35,50,14 GROUPBOX "About this program...",IDC_STATIC,7,7,225,52 CTEXT "An example program showing how to use Dialog Boxes\r\n\r\nby theForger", IDC_STATIC,16,18,144,33END</PRE>On this first line, <CODE>IDD_ABOUTDLG</CODE> is the idof the resource. <CODE>DIALOG</CODE> is the resource type, and the four number are the Left,Top, Width and Height co-ordinates. These ARE NOT PIXELS, they are in DialogUnits, which are based on the size of the font used by the system (and chosen by the user). If you have a large font selected, the dialog will be large, if you use a smaller font, thedialog will be that much smaller. This is important as it makes sure that all of the controlsare the proper size to display their text in the current font. You can convert dialog units to pixels at runtime using <CODE>MapDialogRect()</CODE>. <CODE>DISCARDABLE</CODE> tells thesystem it may swap the resource memory to disk when it's not being used in order to conserve system resources (essentially pointless).<P>The second line starts with <CODE>STYLE</CODE> and follows with the window styles that willbe used to create the dialog. These should be explained under <CODE>CreateWindow()</CODE>in your help files. In order to use the predefined constants you may need to add<CODE>#include "windows.h"</CODE> to your .rc file, or in the case of VC++, <CODE>winres.h</CODE> or <CODE>afxres.h</CODE>will do. If you use the resource editor these files will certainly be included automaticallyif needed.<P>The <CODE>CAPTION</CODE> line should be self explanitory.<P>The <CODE>FONT</CODE> line specifies the size and name of the font you wish to use forthis dialog box. This might not end up exactly the same on each computeras different people will have different fonts and may have specified differentfont sizes. You usually don't need to worry about that though.<P>Now we have the list of controls to create on the dialog<P><PRE> DEFPUSHBUTTON "&OK",IDOK,174,18,50,14</PRE></P>Here's the line for the OK button. The & in this case like with menus underlines thenext letter "O", so that by pressing Alt+O the user can activate this control(part of the default processing I mentioned).<CODE>IDOK</CODE> is the control identifier. <CODE>IDOK</CODE> is pre-defined so we don't need to<CODE>#define</CODE> it ourselves. The four numbers at the end are the left, top, widthand height, all in dialog units.<P>This information should be purely academic, as you almost always use aresource editor to create dialogs, but knowing how to do it from text issometimes necessary, expecially if you have no visual editor.<P>Two of the controls have an ID of <CODE>IDC_STATIC</CODE> (which is -1), this is used to indicate we never need to access them, so they have no need of an identifier. However it doesn't hurt to give them an ID and your resource editor might do so automatically.<P>The <CODE>"\r\n"</CODE> in the text of the static control is a CR-LF pair, the way windowsrepresents a new line.<P>So! Having added that to your .rc file we need to write a Dialog Procedureto process message for this box. Don't worry this is nothing new, it'spracticly the same as our main Window Procedure (but not exactly).<PRE CLASS="SNIP">BOOL CALLBACK AboutDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam){ switch(Message) { case WM_INITDIALOG: return TRUE; case WM_COMMAND: switch(LOWORD(wParam)) { case IDOK: EndDialog(hwnd, IDOK); break; case IDCANCEL: EndDialog(hwnd, IDCANCEL); break; } break; default: return FALSE; } return TRUE;}</PRE>There are a few important differences between a dialog procedure and windowprocedure. One is that you DO NOT call <CODE>DefWindowProc()</CODE> for message you don'thandle. With dialogs this is done automatically for you (and will really screw things up if you do it).<P>Secondly, in general you return FALSE for messages you don't process, and TRUE formessages you do process, UNLESS the message specifies you return somethingelse. Note that this is what we do above, the default is to do nothing and return FALSE,while messages we do handle break the <CODE>switch()</CODE> and return <CODE>TRUE</CODE>.<P>Thirdy, You do not call <CODE>DestroyWindow()</CODE> to close a dialog, you call <CODE>EndDialog()</CODE>. The second paramter is the value that is returned to whatever code called <CODE>DialogBox()</CODE>.<P>Finally, instead of handling <CODE>WM_CREATE</CODE>, you handle <CODE>WM_INITDIALOG</CODE> to do anyprocessing that needs to be done before the dialog appears, and then returnTRUE to have the keyboard focus set to the default control. (You can actually handle <CODE>WM_CREATE</CODE>as well, but it is sent BEFORE any of the controls have been created, so you can't access them. In<CODE>WM_INITDIALOG</CODE> the controls have already been created).<P>Enough chit-chat, lets create it....<PRE CLASS="SNIP">case WM_COMMAND: switch(LOWORD(wParam)) { case ID_HELP_ABOUT: { int ret = DialogBox(GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_ABOUT), hwnd, AboutDlgProc); if(ret == IDOK){ MessageBox(hwnd, "Dialog exited with IDOK.", "Notice", MB_OK | MB_ICONINFORMATION); } else if(ret == IDCANCEL){ MessageBox(hwnd, "Dialog exited with IDCANCEL.", "Notice", MB_OK | MB_ICONINFORMATION); } else if(ret == -1){ MessageBox(hwnd, "Dialog failed!", "Error", MB_OK | MB_ICONINFORMATION); } } break; // Other menu commands... }break;</PRE><P>This is the code I used to create my about box, you can probably guess thatthis is to be merged into your <CODE>WM_COMMAND</CODE> handler, if you aren't clear onthis aspect, you might want to review the section on menus. <CODE>ID_HELP_ABOUT</CODE>is the identifier of my Help -> About menu item.<P>Since we want the menu on our main window to create the dialog, we obviously want to put this code in the <CODE>WndProc()</CODE> of our main window, not the dialog proc.<P>Now I stored the return value from the call to <CODE>DialogBox()</CODE>, this is just soyou can observe the effects of pressing the two buttons, hitting Esc, Enteretc... from inside the dialog. It also illustrates how to use the return valuefrom a dialog box to check for success, failure, a users choice, or whateverother information you choose to send back to the caller from the Dialog Procedure.<PRE CLASS="SNIP">DialogBox(GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_ABOUT), hwnd, AboutDlgProc);</PRE>This is the only important part, and you can choose to put it wherever in yourcode that you want the dialog to come up. <CODE>IDD_ABOUT</CODE> is the id of the dialogresource. <CODE>hwnd</CODE> is the handle to the parent window of the dialog.<CODE>AboutDlgProc()</CODE> is of course the dialog procedure to use to control the dialog.<P>That's it! Sit IDD_UBU, sit.<P>A perticularly astute reader might eventually wonder, if <CODE>DialogBox()</CODE> doesn'treturn untill the dialog closes we can't process messages while it's up, so how does it work? Well the nifty thing about <CODE>DialogBox()</CODE> is that it has it's own messageloop, so while the dialog is displayed, our message loop is out of the picture and thedefault loop is handled by windows. This loop also takes care of fun things like movingthe keyboard focus from control to control when you press Tab.<P>Another effect of using DialogBox is that your main window is disabled untill the dialog isdismissed. Sometimes this is what we want, and sometimes it isn't, such as when we want to use a dialog as a floating toolbar. In this case we want to be able to interact with bothout dialog and our main window, and this will be the focus of the next section.<HR><FONT SIZE="-1">Copyright © 1998-2003, Brook Miles (<A HREF="mailto:forger(nospam)winprog.org">theForger</A>). 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