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May 93 - Three MacApp 3.0.1 Shortcuts

Three MacApp 3.0.1 Shortcuts

Ken Victor

The following three shortcuts have made my life much simpler while developing a new MacApp 3.0.1 application using C++.

Try and Catch Macros

In a past issue of "Develop" magazine, the C macros for Try and Catch were defined for MacApp 2. I got used to using these when I was developing a MacApp 2 product using C++, and although the MacApp 3 approach to exception handling is easier to use with C++, I wanted to continue to use Try and Catch. I find this more meaningful to read than if fi.Try(). So here is my version for MacApp 3:
#define try                    \
    FailInfo fi;            \
    if (fi.Try()) {
#define catch               \
    fi.Success();           \
    }                       \
    else
#define try2                \
    if (fi.Try()) {
#define success     fi.Success()
#define resignal    fi.ReSignal()

Thus you can write code that looks like the following:

try {
    …
    }
catch {
    …
    resignal;
    }

    or:

try …
catch ;

    or:

try {
    …
    success;
    return;
    …
    }
catch ;

These macros nest properly so that you can write the following:

try {
    …
    try {
        …
        }
    catch {
        …
        resignal;
        }
    …
    }
catch {
    …
    resignal;
    }

The Try2 macro is used if you want a second, or third, Try clause at the same level as a previous one. E.g.:

try {
    …
    }
catch {
    …
    resignal;
    }
…
try2 {
    …
    }
catch {
    …
    resignal;
    }

The Catch macro could easily be modified to automatically resignal, but I felt it best not to hide this, and to save the few bytes in the situation where I didn't need to resignal.

TMyDocument Shortcut

When developing a new application, each time you add, change, or delete a class variable from your TMyDocument class, there are up to 8 different methods that you may have to change:
Initialize
IMyDocument
DoInitialState
Free
FreeData
DoNeedDiskSpace
DoRead
DoWrite

And it is important that DoRead and DoWrite perform operations in the same order. I got tired of trying to remember to update each of these methods, and of having to go back and forth between DoRead and DoWrite to make sure I was doing things in the right order. I therefore decided to localize all these functions into one common method. The price I pay for this is a slight performance hit due to the extra switches in my common routine, a slight violation of clean segmentation, and a violation of the tenant of a single routine performing a single function. I felt that these were a small price to pay for the increased convenience. When my app is complete, I can always do away with this common routine, and place the appropriate code in each of the specific methods.

My common routine is defined as follows:

enum tDocIterType {
    forReading,
    forWriting,
    forSizing,
    forInitialize,
    forIDoc,
    forDoInitial,
    forFreeData,
    forFree
    };
void    DoSRWIIDF(  tDocIterType iterType,
                    TFile* aFile,
                    long& dataForkBytes,
                    long& rsrcForkBytes,
                    Boolean modifier = false);

Each of my standard methods is now quite simple and implemented similarly to the following:

pascal void TMyDocument::DoNeedDiskSpace(
                        TFile* itsFile,
                        long& dataForkBytes,
                        long& rsrcForkBytes) {
    // count us
    DoSRWIIDF(  forSizing,
                itsFile, 
                dataForkBytes, 
                rsrcForkBytes);
    }   //  end of TMyDocument :: DoNeedDiskSpace 

My common routine locks the document, so I can read and write to it comfortably, allocates any needed Streams, and for each member variable in the document performs a switch to perform the required action. The core of the code follows:

#pragma segment DocReadWriteEtc
void TMyDocument::DoSRWIIDF(    tDocIterType iterType,
                    TFile* aFile,
                    long& dataForkBytes,
                    long& rsrcForkBytes,
                    Boolean modifier) {
TStream*        aStream = NULL;
VOLATILE( aStream);

// lock us just in case
    SignedByte myState = LockHandleHigh( (Handle) this);

    try {
    // get stream for i/o
        switch (iterType) {
            case forSizing:
                aStream = new TCountingStream;
                ((TCountingStream*) aStream)->ICountingStream();
                aStream->SetPosition( 0);
                inherited::DoNeedDiskSpace( aFile,
                                        dataForkBytes,
                                        rsrcForkBytes);
                break;
            case forReading:
            case forWriting:
                aStream = new TFileStream;
                ((TFileStream*) aStream)->IFileStream( aFile);
                aStream->SetPosition( 0);
                if (iterType == forReading)
                    inherited::DoRead( aFile, modifier);
                else inherited::DoWrite( aFile, modifier);
                break;
            }
    //  field 1
        switch (iterType) {
            case forSizing:     // fall thru
            case forWriting:
                aStream->WriteBytes( &field1, sizeof( field1));
                break;
            case forReading:    
                aStream->ReadBytes( &field1, sizeof( field1));
                break;
            case forInitialize:
                …
                break;
            case forIDoc:
                …
                break;
            case forDoInitial:
                …
                break;
            case forFreeData:
                …
                break;
            case forFree:
                …
                break;
            }
    //  field 2
        …
    // free stream
        if (iterType == forSizing)
            dataForkBytes += aStream->GetSize();
        FreeIfObject( aStream);
    // unlock us
        HSetState( (Handle) this, myState);
    }
catch {
    // free stream
        FreeIfObject( aStream);
    // unlock us
        HSetState( (Handle) this, myState);
    resignal;
    }
}   //  end of TMyDocument :: DoSRWIIDF

Now whenever I add, change, or delete a field, it is a simple matter of modifying the one "block" of code.

Floating TEditTexts

In several of my dialogs, I had fields in which I wanted to restrict what characters the user could enter. I wanted to beep if the user typed an illegal character. In looking at the MacApp3Tech$ archives, the suggestions for accomplishing this basically involved subclassing TEditText and a few other classes so that you could create you own floating TEView with its appropriate behavior. Nick Nallick, in his article "Text Filtering with Behaviors" in the July 1992 FrameWorks describes such an approach. I decided to try the different approach of attaching a Behavior to the dialog floating TEView, and much to my relief this worked out even better than I thought it would, and is in fact a very general approach. You can even attach multiple instances of this behavior to the floating view, and each instance can act on different characters and/or be applied to different TEditTexts in the dialog.

The Behavior basically looks at each character the user types into a TEditText and beeps if this is an illegal character, or if it is a legal character simply passes it along the behavior chain for normal operation. The behavior will also examine each character in a pasted string and beep if the string contains any illegal characters or pass the string along. Using the behavior is quite simple and relies on the fact that there is only one floating TEView per dialog window and that this view is usually the window's target after the window has been created. First create your window and establish it as a dialog so that the floating TEView will exist. Then create the behavior:

TBhvrInputFilter* aCharBeeper = new TBhvrInputFilter;

Then call the '"I" method, passing the window:

aCharBeeper->IBhvrInputFilter( aWindow);

This will initialize the Behavior and attach it to the floating TEView. It finds the floating TEView by first looking at the window's target to see if is a member of TDialogTEView; if not, it searches the window's sub views until it finds a TDialogTEView to attach to.

Next tell the Behavior which TEditText views you wish to check by passing the identifier(s) of these views:

aCharBeeper->AddView( aEditText->GetIdentifier());
aCharBeeper->AddView( anotherEditText->GetIdentifier());

And lastly, tell the behavior which characters are allowed. The default is to not allow any characters. However there are several methods for specifying the legal characters.

aCharBeeper->AllowNumbers();
aCharBeeper->AllowControlChars();
aCharBeeper->AllowChar( '/');

The above sequence will allow numbers and the slash character, the common characters for a date input view, but will beep on all other characters. It will also allow all control characters so that normal editing can take place.

Advantages

This approach relies on the fact that a common single floating TEView is passed around, rather than each TEditText having its own floating TEView. This leads to both the advantages and disadvantages of this approach, as opposed to subclassing TEditText to install your own floating TEView. This approach is simpler to use and requires less code since there is no need to subclass. The disadvantage is that since this behavior is attached to the only floating TEView, each TEditText that you use uses this behavior, even if you don't want to filter that TEditText. The list of views to filter is maintained as a TLongintList and I haven't noticed any unacceptable performance (but I have not made any measurements). This approach is especially useful if you have several TEditTexts that require the same filtering. And, as mentioned above, if you have different filtering requirements, you can simply install multiple instances of this behavior, each with their own set of views to check, and their own set of legal characters.

Post processing

While further developing my app, I had a need to process TEditText after each character's editing action had taken place, but before any other processing could occur. (What I wanted was to perform name lookup and recognition based on the user's [partial] input string.) Since my use of behaviors for filtering input worked so well, I decided to capitalize on what I already had. I broke up TBhvrInputFilter into two classes: TBhvrFTEVFilter and TBhvrInputFilter. TBhvrFTEVFilter is an abstract class with methods for attaching itself to the floating TEView, and for adding, removing, and checking which sub views to work with. TBhvrInputFilter is now a subclass of TBhvrFTEVFilter and contains the specific methods having to do with filtering characters.

I then subclassed TBhvrFTEVFilter again to create a class that would do post processing of the user's input. This turned out to be a little more difficult than I thought it would be at first, but still simpler than any other way I could think of. The difficulty lay in the fact that when I call inherited::DoKeyEvent or inherited::DoMenuCommand, the TDialogTEView actually created command objects, rather than acting immediately. This was solved by my examining the event queue after calling the inherited method, looking for a TTECommand. If I find one, I remove it from the queue, call its DoIt, Commit, and Free methods. I can then easily get the resulting edited text and act as I wish.

In hindsight, I realized that I may have been able to use MacApp's dependency and notification techniques to accomplish this post processing. However, I now had something that worked, and I believe I might have had problems with characters after the first typed character, and "if it ain't broke..."

 
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