How to make a class with nested objects Parcelable

Question

I'd like to make class A Parcelable.

public class A {     public String str;     public ArrayList<B> list; } 

This is what I've come up with so far. However it crashes with a NullPointerException. The problem are these two statements: dest.writeList(list); & in.readList(list, this.getClass().getClassLoader());. I can't figure out what to do from here :(

Class A

public class A implements Parcelable {     public String str;     public ArrayList<B> list;      @Override     public int describeContents() {         // TODO Auto-generated method stub         return 0;     }      @Override     public void writeToParcel(Parcel dest, int flags) {         dest.writeString(str);         dest.writeList(list);     }      private A(Parcel in) {         str = in.readString();         in.readList(list, this.getClass().getClassLoader());     }      public static final Parcelable.Creator<A> CREATOR             = new Parcelable.Creator<A>() {         public A createFromParcel(Parcel in) {             return new A(in);         }          public A[] newArray(int size) {             return new A[size];         }     }; } 

Class B

public class B implements Parcelable {     public String str;      @Override     public int describeContents() {         // TODO Auto-generated method stub         return 0;     }      @Override     public void writeToParcel(Parcel dest, int flags) {         dest.writeString(str);     }      private B(Parcel in) {         str = in.readString();     }      public static final Parcelable.Creator<B> CREATOR             = new Parcelable.Creator<B>() {         public B createFromParcel(Parcel in) {             return new B(in);         }          public B[] newArray(int size) {             return new B[size];         }     }; } 

Thank you for your time.

Answer 1

I finally figured out what to type into Google :), and found this Android, How to use readTypedList method correctly in a Parcelable class?

The solution was to use read-/writeTypedList instead. I also initialize the arraylist to avoid any further NullPointerException.

Class A

public class A implements Parcelable {     public String str;     public ArrayList<B> list = new ArrayList<B>();      @Override     public int describeContents() {         // TODO Auto-generated method stub         return 0;     }      @Override     public void writeToParcel(Parcel dest, int flags) {         dest.writeString(str);         dest.writeTypedList(list);     }      private A(Parcel in) {         str = in.readString();         in.readTypedList(list, B.CREATOR);     }      public static final Parcelable.Creator<A> CREATOR             = new Parcelable.Creator<A>() {         public A createFromParcel(Parcel in) {             return new A(in);         }          public A[] newArray(int size) {             return new A[size];         }     }; } 

Class B

public class B implements Parcelable {     public String str;      @Override     public int describeContents() {         // TODO Auto-generated method stub         return 0;     }      @Override     public void writeToParcel(Parcel dest, int flags) {         dest.writeString(str);     }      private B(Parcel in) {         str = in.readString();     }      public static final Parcelable.Creator<B> CREATOR             = new Parcelable.Creator<B>() {         public B createFromParcel(Parcel in) {             return new B(in);         }          public B[] newArray(int size) {             return new B[size];         }     }; } 

Answer 2

If you have only one Parcelable object inside your main Parcelable object, not list like the accepted answer case. Then it will be like the following:

Class A

public class A implements Parcelable {     public String str;     public B objectB;      @Override     public int describeContents() {         // TODO Auto-generated method stub         return 0;     }      @Override     public void writeToParcel(Parcel dest, int flags) {         //The parcelable object has to be the first one         dest.writeParcelable(objectB, flags);         dest.writeString(str);     }      private A(Parcel in) {         this.objectB = in.readParcelable(B.class.getClassLoader());         str = in.readString();     }      public static final Parcelable.Creator<A> CREATOR             = new Parcelable.Creator<A>() {         public A createFromParcel(Parcel in) {             return new A(in);         }          public A[] newArray(int size) {             return new A[size];         }     }; } 

Class B

public class B implements Parcelable {     public String str;      @Override     public int describeContents() {         // TODO Auto-generated method stub         return 0;     }      @Override     public void writeToParcel(Parcel dest, int flags) {         dest.writeString(str);     }      private B(Parcel in) {         str = in.readString();     }      public static final Parcelable.Creator<B> CREATOR             = new Parcelable.Creator<B>() {         public B createFromParcel(Parcel in) {             return new B(in);         }          public B[] newArray(int size) {             return new B[size];         }     }; } 

IMPORTANT: Please note that the order that you write and read the Parcelable object matters. Checkout this answer for more details