Top Document: comp.windows.x Frequently Asked Questions (FAQ) 7/7 Previous Document: 155) How can I open multiple displays with Xt? Next Document: 157) How do I determine the name of an existing widget? See reader questions & answers on this topic! - Help others by sharing your knowledge It is possible to have code which looks like this trivial callback, which has a clear flow of control. The calls to AskUser() block until answer is set to one of the valid values. If it is not a "yes" answer, the code drops out of the callback and back to an event-processing loop: void quit(Widget w, XtPointer client, XtPointer call) { int answer; answer = AskUser(w, "Really Quit?"); if (RET_YES == answer) { answer = AskUser(w, "Are You Really Positive?"); if (RET_YES == answer) exit(0); } } A more realistic example might ask whether to create a file or whether to overwrite it. This is accomplished by entering a second event-processing loop and waiting until the user answers the question; the answer is returned to the calling function. That function AskUser() looks something like this, where the Motif can be replaced with widget-set-specific code to create some sort of dialog-box displaying the question string and buttons for "OK", "Cancel" and "Help" or equivalents: int AskUser(w, string) Widget w; char *string; { int answer=RET_NONE; /* some not-used marker */ Widget dialog; /* could cache&carry, but ...*/ Arg args[3]; int n = 0; XtAppContext context; n=0; XtSetArg(args[n], XmNmessageString, XmStringCreateLtoR(string, XmSTRING_DEFAULT_CHARSET)); n++; XtSetArg(args[n], XmNdialogStyle, XmDIALOG_APPLICATION_MODAL); n++; dialog = XmCreateQuestionDialog(XtParent(w), string, args, n); XtAddCallback(dialog, XmNokCallback, response, &answer); XtAddCallback(dialog, XmNcancelCallback, response, &answer); XtAddCallback(dialog, XmNhelpCallback, response, &answer); XtManageChild(dialog); context = XtWidgetToApplicationContext(w); while ((RET_NONE == answer) || XtAppPending(context)) XtAppProcessEvent (context, XtIMAll); XtDestroyWidget(dialog); /* blow away the dialog box and shell */ return answer; } The dialog supports three buttons, which are set to call the same function when tickled by the user. The variable answer is set when the user finally selects one of those choices: void response(w, client, call) Widget w; XtPointer client; XtPointer call; { int *answer = (int *) client; XmAnyCallbackStruct *reason = (XmAnyCallbackStruct *) call; switch (reason->reason) { case XmCR_OK: *answer = RET_YES; /* some #define value */ break; case XmCR_CANCEL: *answer = RET_NO; break; case XmCR_HELP: *answer = RET_HELP; break; default: return; } } and the code unwraps back to the point at which an answer was needed and continues from there. Note that modifications are needed to handle receiving WM_DELETE_WINDOW on the window; possibly WM_DELETE_WINDOW can be handled by setting the "answer" variable. [Thanks to Dan Heller (now argv@z-code.com); note that the code in his book caches the dialog but neglects to make sure that the callbacks point to the current automatic "answer".] User Contributions:Top Document: comp.windows.x Frequently Asked Questions (FAQ) 7/7 Previous Document: 155) How can I open multiple displays with Xt? Next Document: 157) How do I determine the name of an existing widget? Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: faq%craft@uunet.uu.net (X FAQ maintenance address)
Last Update March 27 2014 @ 02:12 PM
|
Comment about this article, ask questions, or add new information about this topic: