Passing Data Between Android Activities Using Intents

Introduction

In Android development, transferring data between activities is a common requirement. This tutorial explains how to use Intent along with putExtra() and getExtras() methods to pass data, such as strings, from one activity to another.

Understanding Intents in Android

An Intent is an abstract description of an operation to be performed. It can be used for various purposes, including starting activities, services, or delivering broadcast messages. For our case, intents allow us to start a new activity and pass data between these components seamlessly.

Using putExtra() to Pass Data

To send data from one activity to another, you use the putExtra() method of an Intent. This method allows you to store key-value pairs where keys are strings, and values can be various types like String, int, boolean, etc. Here’s how it is done:

// In Activity A
EditText editText = findViewById(R.id.editText);
Button button = findViewById(R.id.button);

button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Intent intent = new Intent(ActivityA.this, ActivityB.class);
        String dataToSend = editText.getText().toString();
        intent.putExtra("dataKey", dataToSend); // "dataKey" is the key used to retrieve the value later
        startActivity(intent);
    }
});

In this example, ActivityA captures input from an EditText, and on a button click, it creates an Intent to start ActivityB. The text from EditText is passed using putExtra() with a specific key.

Using getExtras() to Retrieve Data

Once the data has been sent via an intent, you can retrieve it in the receiving activity using getIntent().getExtras(), or more simply getIntent().getStringExtra("key") if you expect a string. Here’s how:

// In Activity B
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_b);

    TextView textView = findViewById(R.id.textView);
    
    // Retrieve the data from Intent
    Bundle extras = getIntent().getExtras();
    if (extras != null) {
        String receivedData = extras.getString("dataKey");
        textView.setText(receivedData);  // Displaying the data on a TextView
    }
}

In ActivityB, we retrieve the intent that started this activity, extract the bundle of extras it carries, and then access our string using the key "dataKey". We finally set this retrieved data into a TextView to display.

Shortcuts for Retrieving Data

Starting with API level 12 (Honeycomb), Android provides a more concise way to retrieve data:

String receivedData = getIntent().getStringExtra("dataKey", "defaultValue");

This method allows you to specify a default value that will be used if the key does not exist in the bundle.

Best Practices

1. Use Descriptive Keys: Use clear and descriptive keys when storing data with putExtra(), so it’s easy to identify the purpose of each piece of data.

2. Handle Null Cases: Always check for null values when retrieving extras, as they might not be present if the intent wasn’t set up correctly.

3. Avoid Large Data Transfers: Use intents for lightweight data transfers between activities. For large datasets, consider using a singleton pattern or shared preferences based on your application’s architecture and requirements.

4. Understand Lifecycle Implications: The receiving activity should handle cases where it might be re-created (e.g., due to configuration changes) by checking savedInstanceState.

Conclusion

Passing data between activities in Android is straightforward with the use of Intents and their extras methods. By following this guide, you can effectively send and retrieve small amounts of data across different components of your app, facilitating seamless communication and enhancing user experience.