Koush Ion onCompleted callback - handle CancellationException

Question

I am following an example of the popular Ion library that Koush created: Download a File with a progress bar and I can see from one of his samples that it is possible to send a cancellation using downloading.cancel().

NB: downloading was declared as Future<File>.

When the cancel() method is called it throws a CancellationException. I would like to handle this exception specifically, instead of catching it generally.

My first thought is to wrap a try / catch block, and use something like:

try { 
    //...
} catch (CancellationException ce) {
    //...
}

However if you look at his example, you will see that the onCompleted callback uses 2 inputs: Exception e and File result.

The sample here (line 72) shows this:

if (e != null) {
    Toast.makeText(ProgressBarDownload.this, "Error downloading file", Toast.LENGTH_LONG).show()
    return;
}

This appears to be an alternative to a try / catch block which is generalising an error if an exception exists. However my aim to return a different toast message if the CancellationException was caught.

Answer 1

To handle exceptions individually we can look for the exception type in the instance of the thrown exception e.

This is the solution that works for me:

if (e instanceof CancellationException) {
  //CancellationException was found
}