How to create an application that opens when you drag a file onto it
Lots of applications and programs allow you to open them by dragging a file onto the application icon. The application will then open and load the file you dragged on.
It is quite simple to add this behavior to your LiveCode standalones. In this lesson we will show you how to create a standalone that displays a text file in a field when you drag a text file onto the standalone.
You can download the sample stack from this url: https://tinyurl.com/yaed6zn3
Creating our stack
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.
Getting the filename on Windows
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:
put $1 into field "display"
Building a standalone
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.
Testing the 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.
Loading the text file
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.
put $1 into tFileName
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"
The build the standalone and test it again.
Getting the filename on Mac
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
Accepting text files on Mac
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
<string>IMG Disk Image</string>
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.