Implements parcelable in an object with nested non-primitive elements

Question

I have an object in the form

public class Car implements Serializable, Parcelable {

    private static final long serialVersionUID = 1L;

    String name;
    String description;
    String brand;
    int speed;
    int brake;
    int asset;
    ArrayList<Uri> images;

    public Car(String name, String description, String brand, int speed,
            int brake, int asset, ArrayList<Uri> images) {
        super();
        this.name = name;
        this.description = description;
        this.brand = brand;
        this.speed = speed;
        this.brake = brake;
        this.asset = asset;
        this.images = images;
    }

    public String getName() {
        return name;
    }

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

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public int getSpeed() {
        return speed;
    }

    public void setSpeed(int speed) {
        this.speed = speed;
    }

    public int getBrake() {
        return brake;
    }

    public void setBrake(int brake) {
        this.brake = brake;
    }

    public int getAsset() {
        return asset;
    }

    public void setAsset(int asset) {
        this.asset = asset;
    }

    public ArrayList<Uri> getImages() {
        return images;
    }

    public void setImages(ArrayList<Uri> images) {
        this.images = images;
    }

    public static long getSerialversionuid() {
        return serialVersionUID;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + asset;
        result = prime * result + brake;
        result = prime * result + ((brand == null) ? 0 : brand.hashCode());
        result = prime * result
                + ((description == null) ? 0 : description.hashCode());
        result = prime * result + ((images == null) ? 0 : images.hashCode());
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        result = prime * result + speed;
        return result;
    }

    @Override
    public String toString() {
        return "Car [name=" + name + ", description=" + description
                + ", brand=" + brand + ", speed=" + speed + ", brake=" + brake
                + ", asset=" + asset + ", images=" + images + "]";
    }

    public int describeContents() {
        // TODO Auto-generated method stub
        return 0;
    }

    public void writeToParcel(Parcel dest, int flags) {
        // TODO Auto-generated method stub

    }




}

But I haven't understand how to implements

public void writeToParcel(Parcel dest, int flags) {
    // TODO Auto-generated method stub

}

and

public int describeContents() {
    // TODO Auto-generated method stub
    return 0;
}

that Eclipse have required after the adding of implements Parcelable to the class

on the Android site the sample show also a method

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

What is the right way to make my whole class (and all the nested objects as ArrayList) "Parcelable"?

following the sample I'm arrived to the constructor

public Car(Parcel in) {
   name= in.readString();
 description= in.readString();
speed=in.readInt();
...

images=in.readArrayList(??????????????????);
}

what is the Class loader to pass in readArrayList(..)?

Answer 1

On the writeToParcel method you should do:

public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(brand); //To write String
}

The argument dest in the writeToParcel method has a lot of other methods to write other object or raw types. To put other objects that do not have specific methods in the dest object, you should use the methods writeParcelable if the object you are trying to write implements Parcelable or writeSerializable if the object you are trying to write implements Serializable.

After, when you'll recover your Parceable object, you should use:

private void readFromParcel(Parcel in) {
    brand = in.readString(); //To read String
}

You have to read the values from the in object in the same order you wrote them.

The piece of code:

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

Is necessary to call the readFromParcel method. You should add in your class a constructor to be called from the piece of code above. The constructor should look like:

public Car(Parcel in) {
   readFromParcel(in);
}

About the method describeContents, there is a good answer on Stackoverflow, here.

Summarizing, I've never seen any case in which this method was used. The method is used if you want to release resources after the parsing of the Parcel, but I didin't found any good material on the internet explaining it. Chances are that you'll keep it returning 0. You can found Android documentation for it here.