Vadivelan S R

In Android, objects references cannot be just passed to/from Activities or Fragments simply. To pass or transfer objects from one activity(or fragment) to another activity Intent/Bundle can be used.
To put the objects in Intent/Bundle first our objects should be either one of the below

Serializable
Parcelable

Serializable

Serializable is a marker interface, meaning that there is no method to implement, Java will simply do its best effort to serialize it efficiently.

Problem with Serializable in Android

The problem with Serializable approach is that reflection is used and it is a slow process. This mechanism also tends to create a lot of temporary objects and cause quite a bit of garbage collection.
Serialization is an expensive operation.
Performance of the App gets affected.

An alternative solution is to use Parcelable approach.

Parcelable

It is an Interface for classes whose instances can be written to and restored from a Parcel.

A Parcel is a container for a message (data and object references) that can be sent from one component to another component in android.

Advantages of Parcelable over Serializable

The Parcelable interface will run the code significantly faster as we are being explicit about the serialization process instead of using reflection to infer it.
The code has been heavily optimized which in turn improves app performance.

Parcelable Implementation example

Now we will create a simple app to transfer data from one activity to another activity.

In Android Studio, go to File -> New Project and fill all the details required to create a new project.
Open the layout file your main activity activity_main.xml and add below code. Here the layout contains two TextViews and a Button.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="vertical"
    tools:context=".MainActivity">
    <android.support.design.widget.TextInputLayout
        android:id="@+id/input_layout_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        >
        <EditText
            android:id="@+id/input_name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:singleLine="true"
            android:hint="Enter Name"
            />
    </android.support.design.widget.TextInputLayout>
    <android.support.design.widget.TextInputLayout
        android:id="@+id/input_layout_country"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        >
        <EditText
            android:id="@+id/input_country"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:singleLine="true"
            android:hint="Enter Country"
            />
    </android.support.design.widget.TextInputLayout>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/button_send"
        android:text="Send to ReceiverActivity"
        android:onClick="sendToReceiverActivity"/>
</LinearLayout>

Note: Here Material Design TextInputLayout is used. Check the Design support Library TextInputLayout tutorial to know more.

First we need to create a UserDetails bean class which implements Parcelable interface. The UserDetails class will carry the name and country details.

public class UserDetails implements Parcelable {
    String name;
    String country;

    public String getName() {
        return name;
    }

    public String getCountry() {
        return country;
    }

    public UserDetails(String name, String country){
        this.name = name;
        this.country = country;
    }
    public UserDetails(Parcel in){
        this.name = in.readString();
        this.country = in.readString();
    }
    @Override
    public void writeToParcel(Parcel dest, int flags){
        dest.writeString(name);
        dest.writeString(country);
    }
    @Override
    public int describeContents(){
        return 0;
    }

    public static final Parcelable.Creator<UserDetails> CREATOR
            = new Parcelable.Creator<UserDetails>(){
        public UserDetails createFromParcel(Parcel in){
            return new UserDetails(in);
        }
        public UserDetails[] newArray(int size){
            return new UserDetails[size];
        }
    };
}

Parcelable Interface Explanation:

First a parameterized constructor with a parameter of type Parcel should be passed which will be used to read the Parcel data in a particular order.
```
public UserDetails(Parcel in){
        this.name = in.readString();
        this.country = in.readString();
    }
```
Second, the writeToParcel method need to be overridden. The writeToParcel method writes the fields to a parcel in a particular order.
```
 public void writeToParcel(Parcel dest, int flags){
        dest.writeString(name);
        dest.writeString(country);
    }
```
Third, the describeContents method also need to be overridden and it should return zero. This method is generally not used. Use this link to know more.
```
public int describeContents(){
        return 0;
    }
```

Finally, provide the Parcelable.Creator which is used to create an instance of the class from the Parcel data. The static CREATOR class creates the object from a Parcel via the createFromParcel method that takes in a parcel and passes it to a constructor in the class. The newArray method allows an array of the objects to be parcelled.

 public static final Parcelable.Creator<UserDetails> CREATOR
            = new Parcelable.Creator<UserDetails>(){
        public UserDetails createFromParcel(Parcel in){
            return new UserDetails(in);
        }
        public UserDetails[] newArray(int size){
            return new UserDetails[size];
        }
    };

Now open MainActivity.java and make the changes as mentioned below. This activity contains a textbox and button. When the button is clicked then data from textbox will be sent to the ReceiverActivity.java.

public class MainActivity extends AppCompatActivity {
    EditText inputName;
    EditText inputCountry;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        inputName = (EditText)findViewById(R.id.input_name);
        inputCountry =(EditText)findViewById(R.id.input_country);
    }
    public void sendToReceiverActivity(){
        String name = inputName.getText().toString();
        String country = inputCountry.getText().toString();
        UserDetails userDetails = new UserDetails(name, country);
        Bundle b = new Bundle();
        b.putParcelable("user_details", userDetails);
        Intent i = new Intent(getApplicationContext(), ReceiverActivity.class);
        i.putExtras(b);
        startActivity(i);
    }
}

Here,when the Button is clicked then the UserDetails object is created with the input texts. A Bundle is created and the UserDetails object is put in the Bundle and sent to ReceiverActivity through intents.

The ReceiverActivity.java class will receive the intent and fetches the User details.

public class ReceiverActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_receiver);
        UserDetails userDetails= getIntent().getExtras().getParcelable("user_details");
        TextView receivedText = (TextView)findViewById(R.id.text_received);
        receivedText.setText("Name: " + userDetails.getName() + " Country: " + userDetails.getCountry());
    }

Following is the activity_receiver.xml layout.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" 
    tools:context="com.techkt.parcelableexample.ReceiverActivity">
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_received"/>
</RelativeLayout>

Finally, run and test the app.