Throw a custom exception from a service to an activity

Question

I'm currently working on an XMPP app' on Android and I'm pondering about the best way to throw a different type of Exception than a RemoteException to my activity from my service.

As it seems impossible to throw another thing than a RemoteException using IPC (you can't declare to throw anything in your .aidl), I just see two solutions:

• Create a listener for my activity to listen on my custom XMPP exception, which in fact will not be thrown but just sent as a usual object implementing the Parcelable protocol.

• Catch my XMPPException and throw a RemoteException (with a content updated with my XMPPException) - But in that case, how could I know on my activity if it's an XMPP or a real RemoteException ? By tagging the name of the exception and parsing it on my activity ? It would be really gore.

Do you have any idea ? Did I miss something from the SDK documentation ?

Thanks.

Answer 1

If #1 means what I think it does, I'd use that -- have the service catch the exception and call a method on an AIDL-defined callback object created and supplied by the activity.

You can see an example of that technique in this client and service project, from one of my books.

Answer 2

It looks like we can throw custom exceptions derived from RemoteException. So you can have XMPPRemoteException, or just a generic MyRemoteException that will hold the original exception. Below is a demo for the second case:

Server:

try {
    ...
}
catch(XMPPException e) {
    throw new MyRemoteException(e);
}

Client:

try {
    service.someCall();
}
catch(MyRemoteException e) {
    rethrow(e);
}

Helper method:

private void rethrow(MyRemoteException e) throws Exception {
    if(e.innerException instanceof XMPPException)
        throw (XMPPException)e.innerException;
    else
        throw e.innerException;
}

Exception:

public class MyRemoteException extends RemoteException {
    private static final long serialVersionUID = 1L;
    public Exception innerException;

    public MyRemoteException() {}

    public MyRemoteException(Exception innerException) {
        this.innerException = innerException;
    }
}

Answer 3

I think it is impossible to achieve "Throw a custom exception from a service to an activity". See the resource of Parcel:

    /**
 * Use this function for customized exception handling.
 * customized method call this method for all unknown case
 * @param code exception code
 * @param msg exception message
 */
public final void readException(int code, String msg) {
    switch (code) {
        case EX_SECURITY:
            throw new SecurityException(msg);
        case EX_BAD_PARCELABLE:
            throw new BadParcelableException(msg);
        case EX_ILLEGAL_ARGUMENT:
            throw new IllegalArgumentException(msg);
        case EX_NULL_POINTER:
            throw new NullPointerException(msg);
        case EX_ILLEGAL_STATE:
            throw new IllegalStateException(msg);
    }
    throw new RuntimeException("Unknown exception code: " + code
            + " msg " + msg);
}

so we can know that we just can throw these five exceptions above.

for example: If your service throw a IllegalArgumentException:

    @Override
public void addImage(final int align, final byte[] imageData) throws RemoteException {
    log("/// addImage ///");
    if (imageData == null) {
        throw new IllegalArgumentException("The second argument(image data) can not be empty!");
    }
...
}

your client will can catch it:

            try {
                printer.addImage(0, null);
            } catch (IllegalArgumentException e) {
                e.printStackTrace();
            }