Progress bars are often used to provide a graphical indication of an action measured against time for an ongoing process, such as when transferring files. Here we demonstrate how to implement a progress bar that can be used when importing and exporting a file.

Create a new main stack with two buttons. One button should be labeled Import, the other button should be labeled Export. Then add the progress bar. In a working application, it may be more appropriate to add the file selection dialog, rather than the Import and Export buttons.

The properties of the progress bar are widely configurable. By default the range is set from 0 to 100, with the current value set to 50. For the purpose of this lesson, set the current value to 0. This allows the progress bar to be updated with percentiles.

Note: A range from 0 to 100 is convenient if the percentage values are to be displayed in numerical terms next to the progress bar.

Much of the code in this example is used to determine the size of the file. The repeat loop then reads in the file in 1024 character chunks until the end of file (eof) marker is reached. As the file is read, a counter is incremented to keep track of the amount of data transferred. That value is then used to update the current value of the progress bar.

on mouseUp
   global gFileContents
   # the location of the source file
   # update this line as required
   local tPath, tFileName, tFiles, tFileSize, tImportFileName = "import_me.txt"
   put empty into gFileContents
   set the thumbPosition of scrollbar "Progress Scrollbar" to 0
   # this section of code is used to find the file size and track
   # the progress while reading in the file
   set the itemDel to slash
   put item 1 to -2 of the filename of this stack into tPath
   put (tPath & slash & tImportFileName) into tFileName
   set the directory to tPath
   put the detailed files into tFiles
   # the file name is URL-encoded when using the detailed files 
   # we have to match the encoding here
   filter tFiles with URLEncode(tImportFileName) & "*"
   set the itemDel to comma
   put item 2 of line 1 of tFiles into tFileSize
   
   open file tFileName for read
   put empty into tReadResult
   put 0 into tAmountRead
   repeat while tReadResult is not "eof"
      read from file tFileName for 1024 # read 1k characters
      put the result into tReadResult
      put it after gFileContents
      add length(it) to tAmountRead
      # the following line updates the current position of the progress bar
      set the thumbPosition of scrollbar "Progress Scrollbar" to (tAmountRead/tFileSize)*100
   end repeat
   # if the file uses LF + CR to mark EOL it will be converted to just one of these
   # characters here
   # this means that tAmountRead is slightly smaller than tFileSize
   # compensate for this mismatch by setting the progress bar to 100
   set the thumbPosition of scrollbar "Progress Scrollbar" to 100
   close file tFileName
end mouseUp

As the file is already in memory, it is not necessary to calculate the download size. The export process writes to the file line by line from the internal memory buffer.

on mouseUp
   global gFileContents
   # the location of the target file
   # update this line as required
   local tFileName, tNumLines, tLineCounter, tExportFileName = "export_me.txt"
   set the itemDel to slash
   put item 1 to -2 of the filename of this stack into tPath
   put (tPath & slash & tExportFileName) into tFileName
   open file tFileName for write
   set the thumbPosition of scrollbar "Progress Scrollbar" to 0
   put number of lines of gFileContents into tNumLines
   put 0 into tLineCounter
   repeat for each line tLine in gFileContents
      add 1 to tLineCounter
      write tLine & return to file tFileName
      # the following line updates the current position of the progress bar
      set the thumbPosition of scrollbar "Progress Scrollbar" to (tLineCounter/tNumLines)*100
   end repeat
   
   close file tFileName
end mouseUp

The progress bar should be working now. Use the Import button to load a file into memory and use the Export button to write the file back out to the file system.

If you get an error something like

button "Import": execution error at line 30 (Operators /: divide by zero), char 1

check that the file exists in the same folder as the stack (or whichever folder you may have changed tPath to).