Passing enums through aidl interfaces

Question

As enums aren't primitive types, what's the most effective way to pass an enum through an aidl interface in Android? Is there a way to convert the enum to an ordinal first?

Answer 1

I simply use

String enumString = myEnum.name() 

(with MyEnum as enum and myEnum as value) to get the String representation and then

MyEnum myEnum = MyEnum.valueOf(enumString) 

to reconstruct the enum from the String representation.

Using Ordinals may be a wee bit faster but if I may add Enums later, this is more likely to break old code.

//Edit: As I don't like to have String as return type, I now implemented Parcellable like mentioned here: Passing enum or object through an intent (the best solution)

import android.os.Parcel; import android.os.Parcelable;

enum InitResponse implements Parcelable {
// Everything is fine.
SUCCESS,
// Something else
FOO;


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

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

public static final Creator<InitResponse> CREATOR = new Creator<InitResponse>() {
    @Override
    public InitResponse createFromParcel(final Parcel source) {
        return InitResponse.valueOf(source.readString());
    }

    @Override
    public InitResponse[] newArray(final int size) {
        return new InitResponse[size];
    }
};

}

Answer 2

Non primitive types, other than String, require a directional indicator. Directional indicators include in, out and inout.

Take a look at the official documentation for that: http://developer.android.com/guide/developing/tools/aidl.html#aidlsyntax

Also, you can consider passing the String or ordinal representation of the enum and translate it back when needed. This is taken from the Effective Java 2nd edition:

// Implementing a fromString method on an enum type
private static final Map<String, Operation> stringToEnum = new HashMap<String, Operation>();
static { // Initialize map from constant name to enum constant
    for (Operation op : values())
        stringToEnum.put(op.toString(), op);
} // Returns Operation for string, or null if string is invalid
public static Operation fromString(String symbol) {
    return stringToEnum.get(symbol);
}

In the case above, Operation is an enum.

---

To get the ordinal of an enum consider this example:

public enum Badges{
    GOLD, SILVER, BRONZE;
}

// somewhere else:
int ordinal = Badges.SILVER.ordinal();// this should be 1