Firstly lets create a very simple stack, all we need is a scrolling field which we will use to display the contents of our text file.

Windows standalones start up automatically when a file is dropped on to them. We use the $ keyword to get the name of the file that is dropped onto the standalone. The $ is used to indicate an environment variable on Unix systems and a command-line parameter on Unix or Windows systems.

In this case we will use $1, when a file is dropped onto the standalone $1 contains the path to that file.

We will handle the startup message to retrieve the file name. The startup message is sent to the stack when the application opens. To start we just want to check we are successfully getting the filename so we add this handler to the stack script:

on startup
   put $1 into field "display"
end startup

We need to build a standalone to test our startup handler.

Open the Standalone Application Settings from the File menu and choose OS X and Windows to build for. Leave all the other settings at the defaults.

Then close the Standalone Application Settings and choose Save as Standalone Application from the File menu then choose where you want to build your standalone.

Now go to the folder your standalone application was built in and open the Windows folder, now try dragging a text file onto Text Display.exe. The application will open and the path to the file you dragged on will be displayed in the field.

We don't just want to display the file name though, we want to display the contents of the file so we need to include a handler that will put the contents of our file into the field. At this stage we also want to check that the file is a text file before we display it as our startup handler will accept any type of file.

on startup
	local tFileName
   
	put $1 into tFileName
	loadFile tFileName
end startup

on loadFile pFileName
	## Check that is is a text file
	if char -4 to -1 of pFileName is ".txt" then
		## We use the URL keyword to get the contents of the file 
		put URL ("file:" & pFileName) into field "display"
	end if
end loadFile

The build the standalone and test it again.

On Mac we can't use the $ keyword to get the filename, instead we need to handle the appleEvent message. This message is sent to the current card whenever the application receives an Apple event.

We check what type of appleEvent we get, if it is an open document event then we call our loadFile handler.

on appleEvent pClass, pEventID, pSender
   if pClass is "aevt" then
      ## This is an apple event
      ## We request the data about the apple event
           
      request appleEvent data
      put it into tFileName
           
      if pEventID is "odoc" then
         ## This is an open document event
         loadFile tFileName
      end if
   end if
   pass appleEvent   
end appleEvent

There is another step we need to take in order for our Mac standalone to accept text files. We need to modify the preferences file within the application bundle to specify the file types our application accepts, in this case it is only text files.

Within the application bundle go into the Contents folder and open the info.plist file. You can use a text editor or a plist editor.

We need to add an extra CFBundleTypeExtensions entry stating that the app can open text files. Add

<dict>
	<key>CFBundleTypeExtensions</key>
		<array>
			<string>txt</string>
		</array>
	<key>CFBundleTypeIconFile</key>
	<string>generic.icns</string>
	<key>CFBundleTypeName</key>
	<string>IMG Disk Image</string>
	<key>CFBundleTypeRole</key>
	<string>Viewer</string>
</dict>

after the automatic CFBundleTypeExtensions created by the standalone builder. This states the application can accept files with the extension txt.

If you want your application to accept other file types you need to add a CFBundleTypeExtensions entry for each allowed type.