Virtual Volumes by Erick Tejkowsi 08-01-02 Printer Version

To continue our examinination of the new features in REALbasic 4.5, we'll look at Virtual Volumes this week. If you've ever needed to store different kinds of data in one file, REALbasic's Virtual Volumes are for you!

NOTE: This project requires REALbasic 4.5 or newer!

The new VirtualVolume feature of REALbasic is easy to learn, quick to code, and is a pretty handy tool for your next REALbasic project. The VirtualVolume class lets you store multiple files in one file. This is somewhat like the disk images that you may have used in the Finder. Since REALbasic 4.5 gives you this feature across all of its target platforms (OS9, OSX, and Win32), we'll build today's example using the Classic Mac OS.

Build the Interface

Launch REALbasic and open Window1 from the Project window. To this window, add the following controls:

Arrange the interface however you want. It might look like this:

Source Code

That's it for the interface, now it's time to add some code. The code we'll add goes in the Action event of PushButton1 and PushButton2. First, PushButton1:

  dim f,root,textfile,numberfile as folderItem 
  dim v as virtualVolume
  dim textout as textoutputStream
  dim numout as binaryStream
  dim d as date 
  
  f=DesktopFolder.Child("Resex Virtual Volume")
  v=f.createVirtualVolume
  
  if v<>nil then
    //we have a virtual volme, so let's find it's root
    root = v.Root
    
    //create folderitems for the items
    //we will add to the virtual volume
    textfile = root.child("My Text")
    numberfile = root.child("My Date")
    
    if textfile<>nil then
      //create a text file on the virtual volume
      textout = textfile.createTextFile
      //add some text to it
      textout.writeline "This is text on my virtual volume."
      textout.close
    end if
    
    if numberfile<>nil then
      d=new date 
      //using a generic binary file type here
      //that we didn't even have to define
      //in the file types dialog
      numout = numberfile.createbinaryFile("")
      //store the day, month, and year
      numout.writelong d.day 
      numout.writelong d.month 
      numout.writelong d.Year
      numout.close
    end if
    
  end if
  

Then, it's time for PushButton2

  dim f,root,textfile,numfile as folderItem 
  dim v as virtualVolume
  dim textin as textinputStream
  dim binin as binaryStream
  dim s as string 
  
  f=DesktopFolder.Child("Resex Virtual Volume")
  
  //now open the virtual volume
  v=f.OpenAsVirtualVolume
  
  if v<>nil then
    //we have a virtual volme, so let's find it's root
    root = v.Root
    
    //create folderitems for the items
    //we will retrieve from the virtual volume
    textfile = root.child("My Text")
    numfile = root.child("My Date")
    
    if textfile<>nil and textfile.exists then
      //create a text file on the virtual volume
      textin = textfile.openasTextFile
      //read the text from it
      editfield1.text=textin.readline
      textin.close
    end if
    
    if numfile<>nil and numfile.exists  then
      //get the date from the virtual volume
      binin = numfile.openasbinaryFile(FALSE)
      if binin<>nil then
        //day
        s = str(binin.readlong)+"."
        //month
        s = s + str(binin.readlong)+"."
        //year
        s = s + str(binin.readlong)
        editfield2.text=s 
        binin.close
      end if
      
    end if
    
  end if
  

As you can tell, there isn't much to learn here, but there is much to gain. Creating a VirtualVolume requires use of the new "CreateVirtualVolume" method of the FolderItem class. Once you have a VirtualVolume, you find it's root using the "Root" method. From there, it's standard REALbasic code.

Conclusion

To test the project, select the Debug-Run menu. The demo creates a VirtualVolume on the desktop and adds two files to it. Clicking the other PushButton will retrieve the data from the VirtualVolume. As usual you can download the completed project instead of creating it by hand. Use your imagination when playing with the new VirtualVolume features of REALbasic 4.5. There are many useful possibilities for using this feature:

• As a kind of "virtual" resource fork
• As a way to package your favorite skins in one file
• As a database
• As an archive for easy one-file backups