Android: Custom Object in AIDL

Question

I have an application which interacts with a custom service via two aidl implementations. When the service is ran, I am running into the following exception:

ERROR/AndroidRuntime(9435): FATAL EXCEPTION: main
ERROR/AndroidRuntime(9435): java.lang.NullPointerException
ERROR/AndroidRuntime(9435): at android.os.Parcel.readException(Parcel.java:1328)
ERROR/AndroidRuntime(9435): at android.os.Parcel.readException(Parcel.java:1276)
ERROR/AndroidRuntime(9435): at myservice.IAsyncService$Stub$Proxy.addItems(IAsyncService.java:259)

From this error, I think it is something to do with the marshalling which is carried out. So I checked both aidl implementations; the first aidl (which uses primitives) seemed to work fine (I think because they dont need me to specify imports/implementations); the second (which uses a custom object) however seems to crash giving the above error. I have made sure the custom object correctly implements parcelable (see bottom of post for implementation), and have even tried referencing the custom object from a separate aidl file as shown below.

(Seperate aidl file.) - (IMyItem.aidl)

package myservice;
parcelable myservice.MyItem;

---

(Other aidl file.) - (IAsyncService.aidl)

package myservice;
import myservice.IMyItem;

interface IAsyncService
{
    void addItems(in List<MyItem> itemCollection);
}

---

(Parcelable Implementation) (MyItem)

public class MyItem implements Parcelable
{
    private String name = "";

    public MyItem(String name)
    {
        this.name = name.trim();
    }

    public MyItem(Parcel source) {
        readFromParcel(source);
    }

    public void setItem(String name)
    {
        this.name = name;
    }

    public String getName()
    {
        return this.name;
    }

    public static final Parcelable.Creator<MyItem> CREATOR = new Parcelable.Creator<MyItem>() {
        @Override
        public MyItem[] newArray(int size) {
            return new MyItem[size];
        }

        @Override
        public MyItem createFromParcel(Parcel source) {
            return new MyItem(source);
        }
    };

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel destination, int flags) {
        destination.writeString(this.name);
    }

    public void readFromParcel(Parcel source) {
        this.name = source.readString();
    }
}

Is there something I am missing or have completely overlooked?

Thanks John

Answer 1

What you are seeing is that a NullPointerException has been thrown on the remote side, that exception was returned as a result, and re-thrown to your client. In these situations it helps a lot for debugging to find out what the original exception is. You can do this with a trick:

In your class that implements the interface, override onTransact() to do this:

protected boolean onTransact(int code, Parcel data, Parcel reply, int flags) {
    try {
        super.onTransact(code, data, reply, flags);
    } catch (RuntimeException e) {
        Log.w("MyClass", "Unexpected remote exception", e);
        throw e;
    }
}

Now when the crash happens you will also see in the log the original exception printed, with the line where it happened.