Android - Inter Process Communication

What the best way to do inter process communication (IPC) in Android between activities, the answer is parcelable

you need to implement an interface Parcelable

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

public class UserParcelable implements Parcelable {
    private Integer mID;
    private String mName;
    private String mDescription;

...

} 

 and override the following method:
- writeToParcel(Parcel out, int flags): You should implement serialization of the object.

    @Override
    public void writeToParcel(Parcel out, int flags) {
        out.writeInt(mID);
        out.writeString(mName);
        out.writeString(mDescription);
    } 

- describeContents(): You should define the kind of object, for instance using hashCode().

       
    @Override
    public int describeContents() {

        return hashCode();
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((mDescription == null) ? 0 : mDescription.hashCode());
        result = prime * result + ((mID == null) ? 0 : mID.hashCode());
        result = prime * result + ((mName == null) ? 0 : mName.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        UserParcelable other = (UserParcelable) obj;
        if (mDescription == null) {
            if (other.mDescription != null)
                return false;
        } else if (!mDescription.equals(other.mDescription))
            return false;
        if (mID == null) {
            if (other.mID != null)
                return false;
        } else if (!mID.equals(other.mID))
            return false;
        if (mName == null) {
            if (other.mName != null)
                return false;
        } else if (!mName.equals(other.mName))
            return false;
        return true;

    }
       

- Object CREATOR: You should implement de-serialize your custom data objects from Parcel.

   public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
        public UserParcelable createFromParcel(Parcel in) {
            return new UserParcelable(in);
        }

        public UserParcelable[] newArray(int size) {
            return new UserParcelable[size];
        }
    };
       

- Constructor: You should define a constructor with parcel as argument.

       
    UserParcelable(Parcel in) {
        mID = in.readInt();
        mName = in.readString();
        mDescription = in.readString();
    }
    

It is important to note that using parcelable object than serializable object is sometimes up to 15 times faster. (http://blog.rocapal.org/?p=560)