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November 91 - User Selected Folders & Indexing Through Directories

User Selected Folders & Indexing Through Directories

Dan Wendin

MacApp 2 programmers can usually ignore working directories; however, you need to use them when the user selects a folder and your program accesses the files in it without further user interaction. Selecting a folder gives you a real directory and MacApp 2 usually expects a working directory.

Working directories were introduced with the Hierarchical File System (HFS) in 1986 as a way to maintain compatibility with the original flat file system. They are returned by the standard file dialogs and passed to the MacApp 2 file methods that deal with opening files.

Most applications let MacApp 2 take care of this. And the file manager chapter in Inside Mac Volume IV covers working directories in gruesome detail, making it difficult to sort out what you need to know. Hence this article.

To set the stage, suppose your file-based application has an Export function to generate a text file for a 4D data base application. To make things easier on the 4D application, the user can export any number of files into a single export file with a fixed name. The user puts all the files to be processed into one folder before starting your application. In your application, the user selects a folder and you take care of everything from that point on.

I have implemented a set of file based objects similar to Tom Becker's approach in his April Frameworks article and which (hopefully) anticipate MacApp 3. This is reflected to some extent in the sample code on the FrameWorks Disk.


I adapted the code in DTS's sample code SC.018.StdFile to work with MacApp 2. This puts up a slightly modified version of the selection dialog used by MPW's Set Directory command (Figure 1). This dialog is a real DLOG/DITL resource pair, not a MacApp dialog. Its definition must be copied into one of your myApp.r files and then created using Res.

Once you have it in a myApp.rsrc file, you can change it using ResEdit or AppMaker (the standard AppMaker version 1.1, not the MacApp version 1.2). ViewEdit cannot access these resources.

The Select Button completes the selection process. Double clicking on a folder (or clicking the Open button) opens the folder and displays the folders one level down. The Select Current Folder button keeps the user from having to go up one level to select the current folder.

The call to SFPGetFile that displays the dialog looks like this:

SFPGetFile(where, '', @FoldersOnly, numTypes, pTypeList^,
            @FolderHook, gFolderReply, kGetFoldersDlgId, nil);

FoldersOnly and FolderHook are filter functions. These functions, and any variables they need to access, must be global within their unit. They can't be methods, nor can they be local to the procedure containing SFPGetFile. Tech Note 265, "Pascal To C-PROCEDURE Parameters," explains why-it has to do with limitations in the toolbox with respect to nested procedures.

The FoldersOnly function simply tests the ioFlAttrib field of the parameter block passed to it and returns true if a folder. The parameter numTypes is -1 to tell StdFile to consider all types filtered by FoldersOnly. The pTypeList parameter is ignored-except that it must point to a valid memory location.

The FolderHook function does the real work. The tricky part is that there are only two states for the gFolderReply.good field-true or false-and there is no way to set it to true because the Open button doesn't exit. So FolderHook sets a global flag to true and then acts as if the Cancel button was hit. The Cancel button sets this flag to false. In either case, gFolderReply.good is false, so it is ignored.

FolderHook puts the directory and vRefnum in globals for return to the client. These are the real directory and the real vRefnum. The vRefnum is obtained from low memory location $214, which contains the negative of the current vRefnum. The directory hilighted in the list is in gFolderReply.fType. This is returned in the global if the user clicks the Select button. The current directory is in low memory location $398 and this is returned if the user clicks the Select Current Folder button.

Are there files in the folder? The function ThereAreFiles asks for the first file of the required type using the same function GetFileInFolder that is used to index through the files in the folder. (This is discussed in detail below.)

index := 1;
ThereAreFiles := Self.fFolderDoc.GetFileInFolder(fDirectory,
                                    index, anAppFile, kFileType);

GetFileInFolder returns true if a file is found, and the parameter anAppFile identifies the file. It's ignored here, since we only care whether or not there is a file.

Does the output file already exist?

Because the same file name is used for all export files, I don't want to let the user to destroy an existing file, as the normal SFPPutFile would allow him to do. So, the code needs to check for that case and prevent him from going further. My ThisFileExistsInDir method does this using the toolbox call PBHGetFInfo to get the file's Finder info. The real vRefnum and directory ID are passed in the parameter block's ioVRefnum and ioDirID fields. If successful, then the file exists, and the method returns true:
with pBlock, theAppFile do {an HParamBlockRec}
    ioNamePtr := @fName;
    ioFDirIndex := 0;
    ioVRefnum := vRefnum; {real vRefNum}
    ioDirID := theDirectory
err := PBHGetFInfo(@pBlock, false);
ThisFileExistsInDir := err = noErr


Now it's time to worry about the distinction between real and working directories. The MacApp methods and utility functions that open files expect working directories as their vRefnum parameters. The first thing they do is convert to a real directory and vRefnum. In allocating and opening a file based object, fOutputFile, we switch to a working directory, open the new file and then switch back.
Self.SwitchToWorkDir(theAppFile, itsDirectory);

My SwitchToWorkDir method uses the toolbox call PBOpenWD to open a working directory. It passes the real vRefnum and directory ID, and the application's signature in the parameter block's ioVRefnum, ioWDDirID and ioWDProcID fields, respectively, and gets back the working directory ID in the ioVRefnum field.

with pBlock do {a WDPBRec}
    ioNamePtr := nil;
    ioVRefNum := anAppFile.vRefnum; {the real vRefNum}
    ioWDDirID := theDirectory; {the real directory}
    {program signature}
    ioWDProcID := longint(kSignature); 
    {assign a working ID}
    err := PBOpenWD(@pBlock, false); 
    {switch vRefnum to Working Directory}
    anAppFile.vRefnum := ioVRefNum 
end {with}

This working directory is passed as the vRefnum to OpenNewFile. Because of this doubling up of the ioVRefnum field, the real vRefnum must be available for restoring after the file is opened. OpenNewFile is an adaptation of the MacApp 2 open new file method moved from TApplication.

There are perhaps 40 working directories available to all applications open under MultiFinder under System 6; there are fewer in System 7. There is only one working directory for each file regardless of which application is accessing the file.

Working directories that aren't in use (that is, have no active file buffers associated with them) are closed when the application that opened them quits or if an application explicitly closes them with no active file buffers associated. Therefore, there is the potential of stepping on another application if we explicitly close a working directory. However, I chose to do this rather than risk causing my application and others to run out of working directories. In reality, I have a number of extract files open and, as shown below, we have to do the same thing for the existing files we process.

My RestoreVRefnum method uses the toolbox call PBCloseWD to close the working directory, passing the working directory. It then restores the original vRefnum.

with pBlock do {a WDPBRec}
    ioVRefNum := anAppFile.vRefnum; {the working directory}
    err := PBCloseWD(@pBlock, false); {release working ID}


I use the GetFileInFolder method, mentioned above, to index through the file. The index is set to 1 before calling. The method returns the next file of the requested type and its index. Subsequent calls move the index on to the next file, returning false when the list is exhausted.
index := 1;
fileReturned := aFolderDoc.GetFileInFolder(fDirectory,
                                index, theAppFile, kFileType);
if fileReturned then
      {allocate an object for the file, which opens the file}
        anExtractDoc.ICFExtractDoc(kFileType, kSignature,
                    theAppFile, itsDir, kFileExists, cancelled);

            {process this file if no problem opening}
        if not cancelled then

until not fileReturned;

My GetFileInFolder method first uses the toolbox call PBGetCatInfo to determine if there is an item for the current index and, if so, whether it is a directory or a file. It passes the real vRefnum (from $214), directory and index in the parameter block's ioVRefnum, ioDrDirID and ioFDirIndex fields, respectively. If there is an item, it gets back a pointer to the name and file attributes in the ioNamePtr and ioFlAttrib fields. It returns to the caller with false if there are no more items in the list. It moves on to the next item if ioFlAttrib indicates a directory, not a file.

with block do {a CInfoPBRec}
    ioNamePtr := @theName; {returns file or directory name}
    ioVRefNum := -(SFSaveDisk^); {current volume refnum}
    ioFDirIndex := index;
    ioDrDirID := theDirectory;
    err := PBGetCatInfo(@Block, false)

The toolbox call PBHGetFInfo gets the file type, passing the same fields (the directory is passed in the ioDirID field). The file type in the finder info is returned in ioFlFndrInfo.fdType. If it matches, the real vRefnum and file name are returned to the caller. Otherwise, it moves on to the next item.

with fblock do {HParamBlockRec}
ioNamePtr := @theName; {file name}
ioVRefNum := block.ioVRefNum; {real}
ioFDirIndex := index;
ioDirID := theDirectory;
ferr := PBHGetFInfo(@fBlock, false);

    {continue if not the type requested or an error}
stillLooking := (ferr <> NoErr) or
(ioFlFndrInfo.fdType <> theFileType)

Because TDocument's ReadFromFile method wants a working directory, it is surrounded by calls to SwitchToWorkDir and RestoreVRefnum.

Don't forget to free the file object at the end of the repeat loop. Happy file indexing!


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