Parcelable – How to do that in Android

      26 Comments on Parcelable – How to do that in Android
Passing data between activities is quite easy. You would normally do that using the Bundle packed into an intent. But sometimes you need to pass complex objects from one activity to another. One workaround would be to keep a static instance of the object int your Activity and access it from you new Activity. This might help, but it’s definitely not a good way to do this. To pass such objects directly through the Bundle, your class would need to implement the Parcelable interface.

For example you have a class called Student, which has three fields.
1. id
2. name
3. grade

You can create a POJO class for this, but you need to add some extra code to make it Parcelable. Have a look at the implementation. 

   1: public class Student implements Parcelable{
   2:     private String id;
   3:     private String name;
   4:     private String grade;
   5:  
   6:     // Constructor
   7:     public Student(String id, String name, String grade){
   8:         this.id = id;
   9:         this.name = name;
  10:         this.grade = grade;
  11:     }
  12:     // Getter and setter methods
  13:     .........
  14:     .........
  15:     
  16:     // Parcelling part
  17:     public Student(Parcel in){
  18:         String[] data = new String[3];
  19:  
  20:         in.readStringArray(data);
  21:         this.id = data[0];
  22:         this.name = data[1];
  23:         this.grade = data[2];
  24:     }
  25:  
  26:     @override
  27:     public int describeContents(){
  28:         return 0;
  29:     }
  30:  
  31:     @Override
  32:     public void writeToParcel(Parcel dest, int flags) {
  33:         dest.writeStringArray(new String[] {this.id,
  34:                                             this.name,
  35:                                             this.grade});
  36:     }
  37:     public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
  38:         public Student createFromParcel(Parcel in) {
  39:             return new Student(in); 
  40:         }
  41:  
  42:         public Student[] newArray(int size) {
  43:             return new Student[size];
  44:         }
  45:     };
  46: }

Once you have created this class, you can easily pass objects of this class through the Intent like this, and recover this object in the target activity.

   1: intent.putExtra("student", new Student("1","Mike","6"));

Here, the student is the key which you would require to unparcel the data from the bundle.

   1: Bundle data = getIntent().getExtras();
   2: Student student = data.getParcelable("student");

This example shows only String types. But, you can parcel any kind of data you want. Try it out.

26 thoughts on “Parcelable – How to do that in Android”

  2. Kumar Bibek

    Well, Serializable also helps, but it's too slow as compared to Parcelable. In Android parlance, I assume that your objects that you would need to pass between Activities would not be super complex.

    Implementation-wise, Serializable seems to be a lot simpler, but if you consider the performace, Parcelable wins here.

    ↓
  5. Lonnie VanZandt

    Parceable seems ok for trivial pojos but anything complex is going to require a lot of code to serialize/parcel and to deserialize/un-parcel. Perhaps it's easier to use GSON/JSON to pass the object around as a JSON string and to use Gson().fromJson() when one needs to turn it back into a Java object.

    ↓
  8. Anonymous

    Thas's true. Path is better. But how I can figure out it? For example we have one more member in the class Student : Bitmap photo;
    What is path in this case?

    ↓
  19. Simone

    Hi, you example is very clear but, I have a question:
    If the object change after I passed it as extra, what is the method to see this change on the activity?
    I try be more clear: I have a thread that update the value of an object started with the main activity. When the user request a new activity I pass as extra this object. Now I want to keep updated also the object on the new activity. What is the method to do this?
    Thanks in advance

    ↓
  23. Deco

    My class is more or less identical to your example. Why would I use parceling rather than just use get methods on the three attributes and save them to the savedInstanceState bundle?

    Am I overcomplicating things by using this for instance storage?
    My class is identical to the student class but I intend to store between 1-10 of them.

    ↓
  25. Randall Mitchell

    @deco. Placing parcelable logic in you model class makes the code reusable. At any point you find yourself passing through an intent several or all of the data members of a given object, you should consider using parcelable.

    ↓

  26. Pingback: 我怎样才能让我的自定义对象封装？ – CodingBlog

Leave a Reply