2.2 Windowing Functions

2.2.1 Dialogs

These functions get input from the user and/or display messages.

The result is #f if the user cancels the dialog, the selected pathname otherwise. The returned pathname may or may not exist, although the style of the dialog is directed towards selecting existing files.

If directory is not #f, it is used as the starting directory for the file selector (otherwise the starting directory is chosen automatically in a platform-specific manner, usually based on the current directory and the user’s interactions in previous calls to get-file, put-file, etc.). If filename is not #f, it is used as the default filename when appropriate, and it should not contain a directory path prefix.

Under Windows, if extension is not #f, the returned path will use the extension if the user does not supply one; the extension string should not contain a period. The extension is ignored on other platforms.

The style list can contain 'common, a platform-independent version of the dialog is used instead of a native dialog. Under Mac OS X, if the style list contains 'packages, a user is allowed to select a package directory, which is a directory with a special suffix (e.g., “.app”) that the Finder normally displays like a file. If the list contains 'enter-packages, a user is allowed to select a file within a package directory. If the list contains both 'packages and 'enter-packages, the former is ignored.

Under Windows and X, filters determines a set of filters from which the user can choose in the dialog. Each element of the filters list contains two strings: a description of the filter as seen by the user, and a filter pattern matched against file names.

See also path-dialog%.

The result is #f if the user cancels the dialog, the selected pathname otherwise. The returned pathname may or may not exist, although the style of the dialog is directed towards creating a new file.

If directory is not #f, it is used as the starting directory for the file selector (otherwise the starting directory is chosen automatically in a platform-specific manner, usually based on the current directory and the user’s interactions in previous calls to get-file, put-file, etc.). If filename is not #f, it is used as the default filename when appropriate, and it should not contain a directory path prefix.

Under Windows, if extension is not #f, the returned path will get a default extension if the user does not supply one. If extension is the empty string, then the extension is derived from the user’s filters choice if the corresponding pattern is of the form (string-append "*." extension); if the pattern is "*.*", then no default extension is added. Finally, if extension is any string other than the empty string, extension is used as the default extension when the user’s filters choice has the pattern "*.*". Meanwhile, the filters argument has the same format and auxiliary role as for get-file. In particular, if the only pattern in filters is (string-append "*." extension), then the result pathname is guaranteed to have an extension mapping extension.

Under Mac OS X 10.5 and later, if extension is not #f, the returned path will get a default extension if the user does not supply one. If filters contains as "*.*" pattern, then the user can supply any extension that is recognized by the system; otherwise, the extension on the returned path will be either extension or other-extension for any (string-append "*." other-extension) pattern in filters. In particular, if the only pattern in filters is empty or contains only (string-append "*." extension), then the result pathname is guaranteed to have an extension mapping extension.

Under Mac OS X versions before 10.5, the returned path will get a default extension only if extension is not #f and filters contains only (string-append "*." extension).

The extension argument is ignored under X, and filters can be used to specify glob-patterns.

The style list is treated as for get-file.

See also path-dialog%.

If directory is not #f, it is used on some platforms as the starting directory for the directory selector (otherwise the starting directory is chosen automatically in a platform-specific manner, usually based on the current directory and the user’s interactions in previous calls to get-file, put-file, etc.).

The style argument is treated as for get-file, except that only 'common or 'enter-packages can be specified. The latter matters only under Mac OS X, where 'enter-packages enables the user to select package directory or a directory within a package. A package is a directory with a special suffix (e.g., “.app”) that the Finder normally displays like a file.

See also path-dialog%.

Displays a message to the user in a (modal) dialog, using parent as the parent window if it is specified. The dialog’s title is title. The message string can be arbitrarily long, and can contain explicit linefeeds or carriage returns for breaking lines.

In addition, style can contain 'caution to make the dialog use a caution icon instead of the application (or generic “info”) icon. Alternately, it can contain 'stop to make the dialog use a stop icon. If style contains both 'caution and 'stop, then 'caution is ignored.

The class that implements the dialog provides a get-message method that takes no arguments and returns the text of the message as a string. (The dialog is accessible through the get-top-level-windows function.)

The dialog contains up to three buttons for the user to click. The buttons have the labels button1-label, button2-label, and button3-label, where #f for a label indicates that the button should be hidden.

If the user clicks the button labelled button1-label, a 1 is returned, and so on for 2 and 3. If the user closes the dialog some other way – which is only allowed when style does not contain 'disallow-close – then the result is the value of close-result. For example, the user can usually close a dialog by typing an Escape. Often, 2 is an appropriate value for close-result, especially when Button 2 is a Cancel button.

If style includes 'number-order, then the buttons are displayed in the dialog left-to-right with equal spacing between all buttons, though aligned within the dialog (centered or right-aligned) in a platform-specific manner. Use 'number-order sparingly.

The style list must contain exactly one of 'default=1, 'default=2, 'default=3, and 'no-default to determine which button (if any) is the default. The default button is “clicked” when the user types Return. If 'default=n is supplied but button n has no label, then it is equivalent to 'no-default.

In addition, style can contain 'caution to make the dialog use a caution icon instead of the application (or generic “info”) icon. Alternately, it can contain 'stop to make the dialog use a stop icon. If style contains both 'caution and 'stop, then 'caution is ignored.

The class that implements the dialog provides a get-message method that takes no arguments and returns the text of the message as a string. (The dialog is accessible through the get-top-level-windows function.)

Like message-box, except that

• the dialog contains a check box whose label is check-label;

• the result is two values: the message-box result, and a boolean indicating whether the box was checked; and

• style can contain 'checked to indicate that the check box should be initially checked.

The result is #f if the user cancels the dialog, the user-provided string otherwise.

If style includes 'password, the dialog’s text field draws each character of its content using a generic symbol, instead of the actual character.

The style must contain exactly one of 'single, 'multiple, or 'extended. The styles have the same meaning as for creating a list-box% object. (For the single-selection style, only the last selection in init-choices matters.)

The result is #f if the user cancels the dialog, the list of selections otherwise.

The style argument is provided for future extensions. Currently, style must be the empty list.

The result is #f if the user cancels the dialog, the selected color otherwise.

The style argument is provided for future extensions. Currently, style must be the empty list.

The result is #f if the user cancels the dialog, the selected font otherwise.

The style argument is provided for future extensions. Currently, style must be the empty list.

The result is #f if the user cancels the dialog, , a ps-setup% object that encapsulates the selected PostScript configuration otherwise.

The parent argument is used as the parent window for a dialog if it is specified. The message string might be displayed as a prompt in the dialog. If init-setup is provided, the dialog is initialized to the given configuration, otherwise the current configuration from current-ps-setup is used.

The style argument is provided for future extensions. Currently, style must be the empty list.

The result is #f if the user cancels the dialog, a ps-setup% object that encapsulates the selected configuration otherwise.

2.2.2 Eventspaces

See Event Dispatching and Eventspaces for more information about eventspaces.

See Event Dispatching and Eventspaces for more information about eventspaces.

See Event Dispatching and Eventspaces for more information about eventspaces.

An event dispatch handler must ultimately call the primitive event dispatch handler. If an event dispatch handler returns without calling the primitive handler, then the primitive handler is called directly by the eventspace handler thread.

If on? is provided and #f, Control is passed to the system translation as normal. This setting affects all windows and eventspaces.

If no argument is provided, the result is #t if Control is currently treated specially, #f otherwise.

If on? is provided #f, Option is passed to the system translation as normal. This setting affects all windows and eventspaces.

If no argument is provided, the result is #t if Option is currently treated specially, #f otherwise.

A second (optional) boolean argument indicates whether the callback has a high or low priority in the event queue. See Event Dispatching and Eventspaces for information about the priority of events.

A handler procedure invoked by the system during a call to yield can itself call yield, creating an additional level of nested (but single-threaded) event handling.

See also sleep/yield .

If no argument is provided, yield dispatches an unspecified number of events, but only if the current thread is the current eventspace’s handler thread (otherwise, there is no effect). The result is #t if any events may have been handled, #f otherwise.

If v is 'wait, and yield is called in the handler thread of an eventspace, then yield starts processing events in that eventspace until

• no top-level windows in the eventspace are visible;

• no timers in the eventspace are running;

• no callbacks are queued in the eventspace; and

• no menu-bar% has been created for the eventspace with 'root (i.e., creating a 'root menu bar prevents an eventspace from ever unblocking).

When called in a non-handler thread, yield returns immediately. In either case, the result is #t.

Evaluating (yield 'wait) is thus similar to (yield (current-eventspace)), except that it is sensitive to whether the current thread is a handler thread, instead of the value of the current-eventspace parameter.

If v is an event in Racket’s sense (not to be confused with a GUI event), yield blocks on v in the same way as sync, except that it may start a sync on v multiple times (but it will complete a sync on v at most one time). If the current thread is the current eventspace’s handler thread, events are dispatched until a v sync succeeds on an event boundary. For other threads, calling yield with a Racket event is equivalent to calling sync. In either case, the result is the same that of sync; however, if a wrapper procedure is associated with v via handle-evt, it is not called in tail position with respect to the yield.

Always use (yield v) instead of a busy-wait loop.

Attempting to use certain methods of windows and timers in a shut-down eventspace also raises the exn:misc exception, but the get-top-level-window in area<%> and get-eventspace in top-level-window<%> methods work even after the area’s eventspace is shut down.

2.2.3 System Menus

This procedure is intended for use in deciding whether to include a Quit, About, and Preferences menu item in a frame’s menu. Under Mac OS X, the application Quit menu triggers a call to a frame’s on-exit method, the About menu item is controlled by application-about-handler, and the Preferences menu item is controlled by application-preferences-handler.

This procedure is intended for use in deciding whether to create a menu-bar% instance with 'root as its parent.

The default handler displays a generic Racket dialog.

If the current eventspace is not the initial eventspace, this procedure returns void (when called with zero arguments) or has no effect (when called with a handler).

The default handler is #f.

If the current eventspace is not the initial eventspace, this procedure returns void (when called with zero arguments) or has no effect (when called with a handler).

The default handler queues a call to the can-exit? method of the most recently active frame in the initial eventspace (and then calls the frame’s on-exit method if the result is true). The result is #t if the eventspace is left with no open frames after on-exit returns, #f otherwise.

If the current eventspace is not the initial eventspace, this procedure returns void (when called with zero arguments) or has no effect (when called with a handler).

The default handler queues a callback to the on-drop-file method of the most-recently activated frame in the main eventspace (see get-top-level-edit-target-window), if drag-and-drop is enabled for that frame.

When the application is not running and user double-clicks an application-handled file or drags a file onto the application’s icon, the filename is provided as a command-line argument to the application.

If the current eventspace is not the initial eventspace, this procedure returns void (when called with zero arguments) or has no effect (when called with a handler).

2.2.4 Miscellaneous

The cursor installed by begin-busy-cursor overrides any window-specific cursors installed with set-cursor.

See also is-busy?.

The get operation always returns #"????" and #"????" for Unix or Windows. The set operation has no effect under Unix or Windows.

The result depends on what, and a #f result is only possible when what is 'x-display:

• 'init-file returns the ,path to the user-specific initialization file (containing Racket code). The directory part of the path is the same path as returned for 'init-dir by Racket’s find-system-path. The file name is platform-specific:

  • Unix and Mac OS X: ".gracketrc"

  • Windows: "racketrc.rktl"

• 'setup-file returns the path to the file containing resources used by get-resource; obsolete.

• 'x-display returns a “path” whose string identifies the X display if specified by either the -display flag or the DISPLAY environment variable when GRacket starts under X. For other platforms, or when neither -display nor DISPLAY was specified, the result is #f.

Under Windows, the default is '(ctl). Under Mac OS X, the default is '(cmd). Under X, the default is normally '(ctl), but the default can be changed through the 'GRacket:defaultMenuPrefix preference low-level preference (see Preferences).

If file is #f, platform-specific resource files are read, as determined by find-graphical-system-path with 'setup-file. (Under X, when file is #f, the user’s ".Xdefaults" file is also read, or the file specified by the "XENVIRONMENT" environment variable.)

The format of a resource entry depends on the platform. Windows resources use the standard ".ini" format. X and Mac OS X resources use the standard X resource format, where each entry consists of a section.entry resource name, a colon, and the resource value, terminated by a newline. Section and entry names are case-sensitive.

Under Windows, if section is one of the following strings, then file is ignored, and entry is used as a resource path:

• "HKEY_CLASSES_ROOT"

• "HKEY_CURRENT_CONFIG"

• "HKEY_CURRENT_USER"

• "HKEY_LOCAL_MACHINE"

• "HKEY_USERS"

In that case, the entry argument is parsed as a resource entry path, followed by a backslash, followed by a value name. To get the “default” value for an entry, use the empty name. For example, the following expression gets a command line for starting a browser:

(let ([b (box "")])

(get-resource "HKEY_CLASSES_ROOT"

"htmlfile\\shell\\open\\command\\" b)

(unbox b))

See also write-resource.

See also get-text-extent in dc<%>.

Expressions entered into the graphical read-eval-print loop can be evaluated in an eventspace (and thread) that is distinct from the one implementing the graphical-read-eval-print-loop window (i.e., the current eventspace when graphical-read-eval-print-loop is called).

If no eventspace is provided, or if #f is provided, an evaluation eventspace is created using (make-eventspace) with a new custodian; the eventspace and its threads are be shut down when the user closes the graphical-read-eval-print-loop window. If an eventspace is provided, closing the window performs no shut-down actions on eventspace.

The keymap for the read-eval-print loop’s editor is initialized by calling the current keymap initializer procedure, which is determined by the current-text-keymap-initializer parameter.

The current-prompt-read parameter is used in the current thread to read input. The result is queued for evaluation and printing in the created eventspace’s handler thread, which uses current-eval and current-print. After printing completes for an interaction result, the next expression in read in the original thread, and so on.

If an exn:break exception is raised in the original thread during reading, it aborts the current call to (current-read) and a new one is started. If an exn:break exception is raised in the original thread while waiting for an interaction to complete, a break is sent (via break-thread) to the created eventspace’s handler thread.

Under Windows, only ".wav" files are supported.

Under X, the function invokes an external sound-playing program; looking for a few known programs (aplay, play, esdplay, sndfile-play, audioplay). In addition, a play command can be defined through the 'GRacket:playcmd preference preference (see Preferences). The preference can hold a program name, or a format string containing a single ~a where the filename should be substituted – and used as a shell command. (Don’t use ~s, since the string that is used with the format string will be properly quoted and wrapped in double quotes.) A plain command name is usually better since execution is faster. The command’s output is discarded, unless it returns an error code – in this case the last part of the error output is shown.

Under Mac OS X, Quicktime is used to play sounds; most sound formats (.wav, .aiff, .mp3) are supported in recent versions of Quicktime. In order to play .wav files, Quicktime 3.0 (compatible with OS 7.5 and up) is required.

The receiver-bytes, event-class-bytes, and event-id-bytes arguments specify the signature of the receiving application, the class of the AppleEvent, and the ID of the AppleEvent.

The direct-arg-v value is converted (see below) and passed as the main argument of the event; if direct-argument-v is #<void>, no main argument is sent in the event. The argument-list argument is a list of two-element lists containing a typestring and value; each typestring is used ad the keyword name of an AppleEvent argument for the associated converted value.

The following types of Racket values can be converted to AppleEvent values passed to the receiver:

	#t or #f		→		Boolean
	small integer		→		Long Integer
	inexact real number		→		Double
	string		→		Characters
	list of convertible values		→		List of converted values
	#(file pathname)		→		Alias (file exists) or FSSpec (does not exist)
	#(record (typestring v) ...)		→		Record of keyword-tagged values

If other types of values are passed to send-event for conversion, the exn:fail:unsupported exception is raised.

The send-event procedure does not return until the receiver of the AppleEvent replies. The result of send-event is the reverse-converted reply value (see below), or the exn:fail exception is raised if there is an error. If there is no error or return value, send-event returns #<void>.

The following types of AppleEvent values can be reverse-converted into a Racket value returned by send-event:

	Boolean		→		#t or #f
	Signed Integer		→		integer
	Float, Double, or Extended		→		inexact real number
	Characters		→		string
	List of reverse-convertible values		→		list of reverse-converted values
	Alias or FSSpec		→		#(file pathname)
	Record of keyword-tagged values		→		#(record (typestring v) ...)

If the AppleEvent reply contains a value that cannot be reverse-converted, the exn:fail exception is raised.

If file is #f, the platform-specific resource database is read, as determined by find-graphical-system-path with 'setup-file.

The return value is #t if the write succeeds, #f otherwise. (A failure indicates that the resource file cannot be written.)

If value is an integer outside a platform-specific range, an exn:fail:contract exception is raised.

See also get-resource.