Introduction to Motif Application Development

Part 8: Application Two, editors

 #include <Xm/Xm.h>  #include <Xm/Text.h>    XtAppContext context;   Widget toplevel, text;   void main(argc,argv)     int argc;     char *argv[]; {     Arg al[20];     int ac;       /* create the toplevel shell */     toplevel = XtAppInitialize(&context,"",NULL,0,       &argc,argv,NULL,NULL,0);       /* set the default size of the window. */      ac=0;     XtSetArg(al[ac],XmNwidth,200); ac++;     XtSetArg(al[ac],XmNheight,200); ac++;     XtSetValues(toplevel,al,ac);       /* create a text widget */     ac=0;     XtSetArg(al[ac],XmNeditMode,XmMULTI_LINE_EDIT); ac++;     text=XmCreateText(toplevel,"text",al,ac);     XtManageChild(text);           XtRealizeWidget(toplevel);     XtAppMainLoop(context); } 

Get this code compiled and running. You can type. You can use the arrow keys. You can use the backspace key. You can even select a region and press the backspace key to delete the region. You can click on an arbitrary insertion point with the mouse and insert text. If you type a line longer than the window can hold, the text will scroll automatically.

Motif also provides a scrollable text widget, which combines a scrolled window widget with a text widget. It is created with a convenience function called XmCreateScrolledText. Simply substitute this convenience function for XmCreateText in the above code and recompile. When you run the new program you should see scroll bars.

Obviously, given a widget that does everything for you, it isn't going to be that difficult to create a complete text editor. This is especially true since Motif provides a number of convenience routines for working with text widgets. If you combine a menu bar with a scrolled text widget, you can create a simple text editor with very little code:

 #include <stdio.h>  #include <sys/types.h>  #include <sys/stat.h>   #include <Xm/Xm.h>  #include <Xm/Text.h>  #include <Xm/Form.h>  #include <Xm/PushB.h>  #include <Xm/RowColumn.h>  #include <Xm/CascadeB.h>  #include <Xm/FileSB.h>  #include <Xm/MessageB.h>    /* integer values used to distinguish the call to menuCB. */ #define MENU_OPEN     1 #define MENU_CLOSE    2 #define MENU_QUIT     3   #define MENU_CUT      4 #define MENU_CLEAR    5 #define MENU_COPY     6 #define MENU_PASTE    7   /* integer values used to distinguish the call to dialogCBs. */ #define OK            1 #define CANCEL        2   XtAppContext context; XmStringCharSet char_set=XmSTRING_DEFAULT_CHARSET;   /* all widgets are global to make life easier. */ Widget toplevel, text, form, label, menu_bar; Widget open_option, close_option, quit_option; Widget cut_option, clear_option, copy_option, paste_option; Widget open_dialog, save_dialog;   char *filename=NULL; Boolean text_changed=False;   void change_sensitivity(open_state)     Boolean open_state; /* changes the menu sensitivities as needed for opened    and closed states. */ {     XtSetSensitive(open_option,open_state);     XtSetSensitive(quit_option,open_state);     XtSetSensitive(close_option,!open_state);     XtSetSensitive(cut_option,!open_state);     XtSetSensitive(copy_option,!open_state);     XtSetSensitive(paste_option,!open_state);     XtSetSensitive(clear_option,!open_state); }   void changedCB(w,client_data,call_data)     Widget w;     XtPointer client_data;     XmAnyCallbackStruct *call_data; /* triggered every time a character is inserted or deleted in    the text widget. text_changed is used to decide if file needs    saving or not. */ {     text_changed=True; }   void openCB(w,client_data,call_data)     Widget w;     int client_data;     XmAnyCallbackStruct *call_data; /* handles the file selection box callbacks. */ {     XmFileSelectionBoxCallbackStruct *s =         (XmFileSelectionBoxCallbackStruct *) call_data;     FILE *f;     char *file_contents;     int file_length;     struct stat stat_val;       if (client_data==CANCEL) /* do nothing if cancel is selected. */     {         XtUnmanageChild(open_dialog);         return;     }       if (filename != NULL) /* free up filename if it exists. */     {         XtFree(filename);         filename = NULL;     }       /* get the filename from the file selection box */     XmStringGetLtoR(s-> value, char_set, &filename);       /* open and read the file. */     if (stat(filename, &stat_val) == 0)     {         file_length = stat_val.st_size;         if ((f=fopen(filename,"r"))!=NULL)         {             /* malloc a place for the string to be read to. */             file_contents = (char *) XtMalloc((unsigned)file_length);             *file_contents = '\0';               /* read the file string */             fread(file_contents, sizeof(char), file_length, f);             fclose(f);             file_contents[file_length]='\0';               /* give the string to the text widget. */             XmTextSetString(text, file_contents);             XtFree(file_contents);               /* set up all resources as needed to make menus and                 text widget sensitive. */             change_sensitivity(False);             XtSetSensitive(text,True);             XmTextSetEditable(text,True);             XmTextSetCursorPosition(text,0);             text_changed=False;         }     }     XtUnmanageChild(open_dialog); }   void handle_save() /* saves the edit widget's string to a file. */ {     FILE *f;     char *s=NULL;       if ((f=fopen(filename,"w"))!=NULL)     {         /* get the string from the text widget */         s = (char *)XmTextGetString(text);           if (s!=NULL)          {             /* write the file. */             fwrite(s, sizeof(char), strlen(s), f);               /* make sure the last line is terminated by '\\n'                  so that vi, compilers, etc. like it. */             if (s[strlen(s)-1]!='\n')                  fprintf(f,"\n");             XtFree(s);          }         fflush(f);         fclose(f);     } }   void save_dialogCB(w,client_data,call_data)     Widget w;     int client_data;     XmAnyCallbackStruct *call_data; /* handles save_dialog buttons. */ {     switch (client_data)     {         case OK:             handle_save();             break;         case CANCEL:             break;     }     /* get rid of the text in the text widget and set it so it        can't be used. */     XtSetSensitive(text,False);     XmTextSetEditable(text,False);     XmTextSetString(text,"");       /* change menu sensitivites and make the dialog invisible. */     change_sensitivity(True);     XtUnmanageChild(save_dialog); }   void menuCB(w,client_data,call_data)     Widget w;     int client_data;      XmAnyCallbackStruct *call_data; /* handles menu options. */ {     Time time;       switch (client_data)     {         case MENU_OPEN:             /* make the file selection box appear. */             XtManageChild(open_dialog);             break;         case MENU_CLOSE:             /* if the text was changed, ask the user about saving it.                 If not, lose the text and set the widget insensitve. */             if (text_changed)                 XtManageChild(save_dialog);             else             {                 XtSetSensitive(text,False);                 XmTextSetEditable(text,False);                 XmTextSetString(text,"");                 change_sensitivity(True);             }             break;         case MENU_QUIT:             exit(0);         case MENU_CUT:             time=call_data-> event-> xbutton.time;             XmTextCut(text,time);             break;         case MENU_CLEAR:             XmTextRemove(text);             break;         case MENU_PASTE:             XmTextPaste(text);             break;          case MENU_COPY:             time=call_data-> event-> xbutton.time;             XmTextCopy(text,time);             break;     } }   Widget make_menu_option(option_name,client_data,menu)     char *option_name;     int client_data;     Widget menu; {     int ac;     Arg al[10];     Widget b;       ac = 0;     XtSetArg(al[ac], XmNlabelString,         XmStringCreateLtoR(option_name,char_set)); ac++;     b=XmCreatePushButton(menu,option_name,al,ac);     XtManageChild(b);           XtAddCallback (b, XmNactivateCallback, menuCB, client_data);     return(b); }   Widget make_menu(menu_name,menu_bar)     char *menu_name;     Widget menu_bar; {     int ac;     Arg al[10];     Widget menu, cascade;       ac = 0;     menu = XmCreatePulldownMenu (menu_bar, menu_name, al, ac);       ac = 0;     XtSetArg (al[ac], XmNsubMenuId, menu);  ac++;     XtSetArg(al[ac], XmNlabelString,         XmStringCreateLtoR(menu_name, char_set)); ac++;     cascade = XmCreateCascadeButton (menu_bar, menu_name, al, ac);     XtManageChild (cascade);        return(menu); }   void create_menus(menu_bar)     Widget menu_bar; {     int ac;     Arg al[10];     Widget menu;       menu=make_menu("File",menu_bar);     open_option = make_menu_option("Open",MENU_OPEN,menu);     close_option = make_menu_option("Close",MENU_CLOSE,menu);     XtSetSensitive(close_option,False);     quit_option = make_menu_option("Quit",MENU_QUIT,menu);       menu=make_menu("Edit",menu_bar);     cut_option = make_menu_option("Cut",MENU_CUT,menu);     copy_option = make_menu_option("Copy",MENU_COPY,menu);     paste_option = make_menu_option("Paste",MENU_PASTE,menu);     clear_option = make_menu_option("Clear",MENU_CLEAR,menu); }   void main(argc,argv)     int argc;     char *argv[]; {     Arg al[10];     int ac;       /* create the toplevel shell */     toplevel = XtAppInitialize(&context,"",NULL,0,       &argc,argv,NULL,NULL,0);       /* default window size. */     ac=0;     XtSetArg(al[ac],XmNheight,200); ac++;     XtSetArg(al[ac],XmNwidth,200); ac++;     XtSetValues(toplevel,al,ac);       /* create a form widget. */     ac=0;     form=XmCreateForm(toplevel,"form",al,ac);     XtManageChild(form);           /* create a menu bar and attach it to the form. */     ac=0;     XtSetArg(al[ac], XmNtopAttachment,    XmATTACH_FORM); ac++;     XtSetArg(al[ac], XmNrightAttachment, XmATTACH_FORM); ac++;     XtSetArg(al[ac], XmNleftAttachment,   XmATTACH_FORM); ac++;     menu_bar=XmCreateMenuBar(form,"menu_bar",al,ac);     XtManageChild(menu_bar);       /* create a text widget and attach it to the form. */     ac=0;     XtSetArg(al[ac], XmNtopAttachment,    XmATTACH_WIDGET); ac++;     XtSetArg(al[ac], XmNtopWidget, menu_bar); ac++;     XtSetArg(al[ac], XmNrightAttachment, XmATTACH_FORM); ac++;     XtSetArg(al[ac], XmNleftAttachment,   XmATTACH_FORM); ac++;     XtSetArg(al[ac], XmNbottomAttachment,   XmATTACH_FORM); ac++;     XtSetArg(al[ac],XmNeditMode,XmMULTI_LINE_EDIT); ac++;     text=XmCreateScrolledText(form, "text", al, ac);     XtAddCallback (text, XmNvalueChangedCallback, changedCB, NULL);     XtManageChild(text);     XtSetSensitive(text,False);     XmTextSetEditable(text,False);       create_menus(menu_bar);       /* create the file selection box used by open option. */     ac=0;     XtSetArg(al[ac],XmNmustMatch,True); ac++;     XtSetArg(al[ac],XmNautoUnmanage,False); ac++;     open_dialog=XmCreateFileSelectionDialog(toplevel,       "open_dialog",al,ac);     XtAddCallback (open_dialog, XmNokCallback,openCB, OK);     XtAddCallback (open_dialog, XmNcancelCallback, openCB, CANCEL);     XtUnmanageChild(XmSelectionBoxGetChild(open_dialog,         XmDIALOG_HELP_BUTTON));       /* create the file saving dialog. */     ac=0;     XtSetArg(al[ac], XmNmessageString,         XmStringCreateLtoR("The text was changed. Save it?",             char_set));  ac++;     save_dialog=XmCreateMessageDialog(toplevel,"ok_dialog",al,ac);     XtAddCallback(save_dialog,XmNokCallback,save_dialogCB,OK);     XtAddCallback(save_dialog,XmNcancelCallback,save_dialogCB,CANCEL);     XtUnmanageChild(XmMessageBoxGetChild(save_dialog,         XmDIALOG_HELP_BUTTON));       XtRealizeWidget(toplevel);     XtAppMainLoop(context); } 

This is a faily long piece of code, but it is very straightforward. This code consists of the menu bar from tutorial six, along with a scrollable text widget, both of which have been attached to a form. Note that the attachments in the main procedure for both the menu bar and the scrolled text widget are specified AT CREATION. The scrolled text widget in particular must have its attachments specified here or it won't attach correctly. The menu code has been set up so that the client_data type is an integer, but other than that it's the same as in tutorial six.

The main function also creates one new widget, called a "file selection box". This widget gives users an easy way to select files. It activates a callback once the user selects a file, and the file name selected by the user is extracted in a manner identical to that used on a selection box.

The openCB callback routine handles the file selection box callback. It extracts the file name, reads the file into a character array, and then gives this string to the text widget. The reverse is done to save a file: the character array is copied from the text widget and placed in a file. Both openCB and handle_save are careful to enable and disable the text widget as needed so that the user cannot edit if there is nothing to be edited.

Note that the menu options for cut, copy and paste are implemented with just one line of code. The text widget provides convenience functions that make clipboard access easy.

This obviously isn't a complete editor, but it does demonstrate how generally easy it is to create a lot of capability with a little bit of code. For a more complete example, see the nmg_editor example in the ITI FTP site as described in tutorials 2 and 3.

• Go to next article in series
• Go to series introduction
• Go to the Interface Technologies on-line training center
• Go to the ITI home page
• Go to more information about ITI on-site corporate training