A simple project to demonstrate how to pass an object between Android activities
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README.md

demo-parcel

A simple project to demonstrate how to pass an object between Android activities

Screenshots

activity-1 activity-2

Passing an object from between activities needs some extra efforts, there are at least three ways to archive this goal:

  1. Using a serializable interface
  2. Using a parcelable interface
  3. Using Google's Gson library to convert from an object to a JSON string

Scenario

For instance, passing two strings to another activity could be archived like this:

Intent intent = new Intent(context, SecondActivity.class);
intent.putExtra(KEY_DOG_NAME, dogName);
intent.putExtra(KEY_DOG_OWNER, dogOwnerName);

If there are too many parameters, we can encapsulate them into a dog object:

public class Dog {

    private String mName;
    private String mOwner;

    public Dog(String name, String owner) {
        this.mName = name;
        this.mOwner = owner;
    }
    ...
}

However, Only primitive types, serializable and parcelable could be transferred to another activity. In the following, I will demonstrate how to get these done with examples.

Serializable

public class SerializableDog extends Dog implements Serializable {

    private String mName;
    private String mOwner;

    public SerializableDog(String name, String owner) {
        super(name, owner);
        this.mName = name;
        this.mOwner = owner;
    }

    @Override
    public String getName() {
        return mName;
    }

    @Override
    public String getOwnerName() {
        return mOwner;
    }
}

Here is an example that a SerialzableDog class extends Serializable. Please note that we need to define the data fields must be defined here.

Parcel

Parcel is a container for a message(data and object reference) that can be sent through an IBinder. Here is a basic example:

public class ParcelableDog extends Dog implements Parcelable {

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

    @Override
    public void writeToParcel(Parcel out, int flags) {
        out.writeString(getName());
        out.writeString(getOwnerName());
    }

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

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

    public ParcelableDog(Parcel in) {
        super(in.readString(), in.readString());
    }

    public ParcelableDog(String name, String owner) {
        super(name, owner);
    }
}

Gson

Using Gson, you don't need to modify the existing object implementation.

Serialize an object to JSON string:

String dogJson = new Gson().toJson(new Dog("Dodo", "Cody"));
startActivity(SecondActivity.newIntent(this, dogJson));

Deserialize JSON string to a basic object:

String dogGson = getIntent().getStringExtra(KEY_DOG_GSON);
if(dogGson != null){
    Gson gson = new Gson();
    Dog dog = gson.fromJson(dogGson, Dog.class);
}

Conclusion

  1. Serializable is easier to implement than parcel
  2. Parcel is faster, but it is only available on Android and it is not appropriate to save into a file.
  3. Parcel array could be passed via intent
  4. Gson is the most straightforward way to use. No modification needed to existed classes