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The V C++ GUI Reference Manual - Vers. 1.20 - 6/30/98
Copyright © 1998, Bruce E. Wampler
This chapter covers the top level classes used to build an application.
The classes covered in this chapter include:
The vApp class serves as the base class for building
applications. There must be exactly one instance of an object
derived from the vApp class. The base class contains and
hides the code for interacting with the host windowing system,
and serves to simplify using the windowing system.
You will usually derive a class based on vApp that will
serve as the main control center of the application, as well as
containing the window objects needed for the user interface.
The single instance of the application class is defined
in the body of the derived application class code.
The vApp class has several utility methods of general
usefulness, as well as several methods that are normally
overridden to provide the control interface from the application
to the command windows. The derived class will
also usually have other methods used to interface with the
application.
In order to simplify the control interface between the application
and the windows, the vAppWinInfo class has been provided.
The application can extend that class to keep track of
relevant information for each window. When the NewAppWin
method is used to create a window, it will create an
appropriate instance of a vAppWinInfo object, and return
a pointer to the new object. The
base vApp then provides the method getAppWinInfo
to retrieve the information associated with a given window.
simSDI This
optional parameter is used to specify
that
Vshould start as a Windows SDI application if it is set
to 1. This parameter has no effect for the X version.
fw, fh These are used to specify the size of a
menuless and canvasless
Vapplication, and are optional.
Your program will not have a C main function. The main
reason for this is portability. While you would usually have
a main in a Unix based program, MS-Windows does not
use main, but rather PASCAL WinMain. By handling
how the program gets started and providing the AppMain
mechanism,
V allows you to ignore the differences. You will
still have all the capability to access the command line arguments
and do whatever else you would do in main without having
to know about getting the host windowing system up and running.
The windowing system will have been initialized before AppMain
is called. You can process the command line arguments, and
perform other required initializations. The top level command
window should also created in AppMain by calling NewAppWin.
Before AppMain is called, the single instance of your
derived vApp object must also be constructed, usually by
instantiating a static instance with a statement such as static
myApp* MyApp = new myApp("ProtoApp"). As part of the
construction of the myApp object, the global pointer
vApp* theApp is also pointed to the single instance of the
vApp or derived myApp object. You can then use
theApp anywhere in your code to access methods provided by
the vApp class.
Your AppMain should return a 0 if it was successful. A
nonzero return value will cause the
V system to terminate with
an exit code corresponding to the value you returned.
The CloseAppWin method is also called when the user clicks
the close button of the window. This close button will
correspond to the standard close window button depending on the
native windowing system. On the X Window System, each window will
have a close button in the menu bar. On Windows, this corresponds
to a double click on the upper left box of the title bar, or
the ``X'' box in Windows 95. To abort this "close all" procedure,
return 0 from your class.
The default behavior of the base NewAppWin class is to set
the window title to name, and the width w and
height h. Note that the height and width are of the
canvas, and not necessarily the whole app window. If you
don't add a canvas to the command window, the results are not
specified. Usually, your derived NewAppWin will create an
instance of your derived vCmdWindow class, and you will
pass its pointer in the win parameter. If the the win
parameter is null, then a standard vCmdWindow will be
created automatically, although that window won't be particularly
useful to anyone.
Your NewAppWin class may also create an instance of your
derived vAppWinInfo class. You would pass its pointer to the
winInfo parameter. If you pass a null, then the base NewAppWin
method also creates an instance of the standard vAppWinInfo
class.
The real work done by the base NewAppWin is to register
the instance of the window with the internal
V run time system.
This is why you must call the base NewAppWin method.
NewAppWin returns a pointer to the object just created. Your
derived code can return the value returned by the base
vApp::NewAppWin, or the pointer it created itself.
The following shows a minimal example of deriving a NewAppWin
method.
Note that it is up to you to implement clipboard interaction.
The vTextCanvasPane does not provide automatic clipboard
support. Thus, your app needs to respond to cut, copy, and paste
commands. The clipboard code will send a message to your
Command Window to control the sensitivity of the M_Paste
command.
V provides two different approaches to handling compute bound
applications. The most straight forward approach is to have
the computation periodically call the
V method vApp::CheckEvents.
CheckEvents will process events, and pass the messages to the
appropriate
V method. This method may be the most appropriate
for applications such as simulations.
The second technique is to have the
V system call a work procedure
periodically to allow some computation to be performed. This technique
may be most appropriate for applications that have short computations
that should be performed even if the user is not entering commands
or interacting with the application. The technique is supported by
the WorkSlice method.
V uses a standard
V vTimer object to implement this
behavior. Thus, all of the information about actual time intervals
and limits on the number of timers discussed in the vTimer
description apply to EnableWorkSlice and WorkSlice.
vWindow, vAppWinInfo
This class is intended to be used as a base class for deriving
your own myAppWinInfo class. The purpose of such a class is
to serve as a controller data base for the MVC architecture. Typically,
you would keep an AppWinInfo record for each view (open window)
of the file or whatever represented by the model. For example, if
your application were a text file viewer, the AppWinInfo record
could track the file name, current line number, and viewing mode
for each view of a file.
V makes using a AppWinInfo object easier by
automatically tracking it when you create each new window with
NewAppWin. You can then easily retrieve the AppWinInfo
object associated with each window by using the vApp::getAppWinInfo
method.
vApp
Chapter 4
The Application
4.1 vApp
The base class for building applications.
Synopsis
Description
Constructor
vApp(char* appName)
vApp(char* appName, simSDI = 0, int fh = 0, int fw = 0)
appName Default name for the application. This name
will be used by default when names are not provided for windows.
The name also appears on the ``main window'' for some platforms,
including Microsoft Windows, but not X.
The constructor also initializes some internal state information.
There must be exactly one instance of the vApp object, and
will usually represent your derived myApp object. See the
code below with AppMain for an example of creating the
single app instance.
Methods to Override
void AppCommand(vWindow* win, ItemVal val)
Any window commands not processed by the vWindow object
are passed to AppCommand. You can override this method
to handle any commands not processed in windows.
int AppMain(int argc, char** argv)
This is a global function (not a class member!) that is called
once by the system at start up time with the standard command
line arguments argc and argv. You provide this
function in your code.
Example
// EVERY V application needs the equivalent of the following line
static myApp* MyApp = new myApp("ProtoApp"); // Construct the app.
//==========================>>> AppMain <<<===========================
int AppMain(int argc, char** argv)
{
// Use AppMain to perform special app initialization, and
// to create the main window. This example assumes that
// NewAppWin knows how to create the proper window.
(void) theApp->NewAppWin(0, "Prototype V Example", 350, 100, 0);
return 0;
}
int CloseAppWin(vWindow* win)
This is the normal way to close a window. Your derived CloseAppWin
should first handle all housekeeping details, such as saving the
contents of a file, and then call the default vApp::CloseAppWin
method. Your code can abort the close process by
not calling
the default vApp::CloseAppwin class, and instead returning
a 0. When you call the default method, the window's CloseWin
method is called and the window removed.
Example
//======================>>> videApp::CloseAppWin <<<===========================
int videApp::CloseAppWin(vWindow* win)
{
// This will be called BEFORE a window has been really closed.
videCmdWindow* cw = (videCmdWindow*)win; // get our cmd window
if (cw->CheckClose()) // check if OK to close
return vApp::CloseAppWin(win); // if OK, then call vApp method
else
return 0; // otherwise, abort close process
}
void Exit(void)
This is the normal way to exit from a standard
V application. The
overridden method can perform any special processing (e.g.,
asking ``Are you sure?'') required. The default Exit will
call CloseAppWin for each window created with NewAppWin,
and then exit from the windowing system.
void KeyIn(vWindow* win, vKey key, unsigned int shift)
Any input key events not handled by the vWindow object are
passed to VApp::KeyIn. See KeyIn in the vWindow
section for details of using keys.
vWindow* NewAppWin(vWindow* win, char* name, int w, int h,
vAppWinInfo* winInfo)
The purpose of the NewAppWin method is to create a
new instance of a window. Most likely, you will override
NewAppWin with your own version, but you still
must
call the base vApp::NewAppWin method
after your
derived method has completed its initializations.
Example
vWindow* myApp::NewAppWin(vWindow* win, char* name, int w, int h,
vAppWinInfo* winInfo)
{
// Create and register a window. Usually this derived method
// knows about the windows that need to be created, but
// it is also possible to create the window instance outside.
vWindow* thisWin = win;
vAppWinInfo* theWinInfo = winInfo;
if (!thisWin) // Normal case: we will create the new window
thisWin = new myCmdWindow(myname, w, h); // create window
// Now the application would do whatever it needed to create
// a new view -- opening a file, tracking information, etc.
// This information can be kept in the vAppWinInfo object.
if (!theWinInfo) // Create if not supplied
vAppWinInfo* theWinInfo = new myAppWinInfo(name);
// Now carry out the default actions
return vApp::NewAppWin(thisWin, name, w, h, theWinInfo);
}
Utility Methods
char* ClipboardCheckText()
Returns 1 if there is text available on the clipboard.
void ClipboardClear()
Clears the contents of the clipboard. Deactivates
M_Paste.
char* ClipboardGetText()
If there is text on the clipboard, this method will return
a pointer to that text.
int ClipboardSetText(char* text)
This will set the system clipboard to the value of text.
It will also send a vApp::SetValueAll message to each of
your windows to set any command object M_Paste to sensitive.
(Whenever the clipboard is emptied, a message to set M_Paste
insensitive is also sent.)
int DefaultHeight()
Returns a default window canvas height value in pixels corresponding to 24 lines
of text in the default font.
int DefaultWidth()
Returns a default window canvas width value in pixels corresponding to 80 columns
of text in the default font.
vFont GetDefaultFont(void)
This method returns a vFont object representing the default
system font. It is a convenience method, and probably not overly useful
to application programs.
vFont GetVVersion(int& major, int& minor)
Returns the current major and minor version of
V.
int IsRunning()
This method returns true if the windowing system is active and
running. A false return means the program was started from
a nonwindowing environment.
int ScreenHeight()
Returns the overall height of the physical display screen in pixels.
Note that this value may or may not be overly useful. On X,
the vCommandWindows are drawn on the full display. On
the Windows MDI version, the command windows all fall inside the
MDI frame, and thus knowing the size of the whole screen is less
useful.
int ScreenWidth()
Returns the overall width of the physical display screen in pixels.
See ScreenHeight.
void SendWindowCommandAll(ItemVal id, int val, CmdType ctype)
This method can be used to send a message to the WindowCommand method
of
ALL currently active windows. This method is most useful for
sending messages to windows from modeless dialogs. While messages to
the WindowCommand method usually originate with the system
in response to menu picks or command object selection, it can be
useful to send the messages directly under program control. The
vDraw sample program contains a good example of using
SendWindowCommandAll (and SetValueAll) in vdrwdlg.cpp.
There is no way to send a message to a specific window. The message
is sent to all active windows.
void SetAppTitle(char* title)
This method is used to set the title of the main application
window. This currently only applies to the Microsoft Windows
MDI version of
V. It is a no-op for the X version. It is still
important that you choose a good title for your main window,
and set it either with this method, or by providing a good
name to the vApp initializer.
void SetValueAll(ItemVal itemId, int Val,
ItemSetType what)
This method is similar to vWindow::SetValue, except that
the control with the given itemId in
ALL currently
active windows is set. This is useful to keep control values
in different windows in sync. The only difference between
vApp :: SetValueAll and vWindow :: SetValueAll is
that the vApp version can be easily called from dialogs
as well as windows.
void SetStringAll(ItemVal itemId, char* title)
This method is similar to vWindow::SetString, except that
the string with the given itemId in
ALL currently
active windows is set. This is useful to keep control strings
in different windows in sync. The only difference between the
vApp::SetStringAll version and the vWindow::SetStringAll
version is that the vApp version can be easily called from
dialogs as well as windows.
int ShowList()
This method is intended mostly for debugging, and will print
on stderr the list of currently registered windows.
vAppWinInfo *getAppWinInfo(vWindow* win)
This method provides an easy way to retrieve the vAppWinInfo
(or more typically, a derived class) object that is associated
with a window. By convention, when a window is first created,
it and its associated vAppWinInfo object are tracked by
NewAppWin. When a user action in a window causes a method
in vApp to be invoked, the this of that window is
usually sent to the vApp method. You then use that
vWindow pointer to call getAppWinInfo to get a
pointer to the associated vAppWinInfo object. It will be
up to you to determine what information that object has, and how
to use it.
Tasking
Some applications may have extensive computation requirements. In
traditional programming environments, this is usually no problem.
However, for GUI based applications, the code cannot simply
perform extensive computation in response to some command event
(such as a "Begin Computation" menu command). GUIs make a basic
assumption that the application will process events relatively
quickly. While computation is in process, the application will
not receive additional events, and may appear to hang if the
computation is too long.
CheckEvents()
Most
V applications will
not need this utility. However, it is possible
for some compute bound applications to lock out system response to the
events needed to update the screen. If you notice that your application
stops responding to input, or fails to consistently update items
in your window, then place calls to vApp::CheckEvents() in
your code somewhere. You may have to experiment how often you need
to call it. It does have some overhead, so you don't want it to
slow down your app. But it does need to get called enough so the
system can keep up with the screen updates. This function needs
no parameters, and returns no value.
EnableWorkSlice(long slice)
For applications that need computations to be performed continuously
or periodically, even while the user is not interacting with the program,
V provides EnableWorkSlice and WorkSlice. After
EnableWorkSlice has been called,
V will call the app's
WorkSlice method every slice milliseconds.
The WorkSlice method of every open vCommandWindow
will also be called. Calling EnableWorkSlice with a zero
value will stop the calls to the WorkSlice methods.
WorkSlice()
When a EnableWorkSlice has been called with a positive value,
V calls vApp::WorkSlice at approximately the specified
interval (or more
likely, the overridden method in your app), as well as the
vWindow::WorkSlice method of each open vCommandWindow.
Your application can override the appropriate WorkSlice
method to perform short, periodic computations. Theses
computations should be shorter than the time interval specified for
EnableWorkSlice. This may be difficult to ensure since
different processors will work at different speeds. One simple
way to be sure you don't get multiple calls to the WorkSlice
method is to set a static variable on entry to the code. Note
that vCommandWindow also has a WorkSlice method.
The WorkSlice for the vApp is called first,
followed by a call to each open vCommandWindow
sequentially in no specific order.
See Also
4.2 vAppWinInfo
A utility class to interface views to models.
Synopsis
Description
Constructor
vAppWinInfo(char* infoName = "", void* ptr = 0)
You can provide two values for the vAppWinInfo constructor.
The first is a pointer to a character string which you can use
to store some name meaningful to you application. The second is a
void * pointer, and can be used to point to anything you
want. The constructor makes a copy of the name string, but just
copies the void pointer and does not copy the object pointed to.
Utility Methods
virtual char* infoName()
Returns a pointer to the name supplied to the constructor.
virtual void* getPtr()
Returns the value of the pointer name supplied to the constructor.
See Also
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