Using Intents to Create Flows

Overview

Intent is a powerful concept within the Android universe. An intent is a message that can be thought of as a request that is given to either an activity within your own app, an external application, or a built-in Android service.

Think of an intent as a way for an Activity to communicate with the outside Android world. A few common tasks that an intent might be used for:

• Take the user to another screen (activity) within your application
• Take the user to a particular URL within the Android web browser
• Take the user to the camera to have them take a picture
• Initiate a call for the user to a given number

As you can see, the Intent is a core part of user flows in Android development. The Intent object itself is a class that represents a particular "request" including the topic of the request and any request "parameters" which are called the Bundle.

Explicit Intents

An "explicit" intent is used to launch other activities within your application. For example, if you the user presses the "compose" button and you want to bring up an activity for them to compose a message, you would launch that second activity using an explicit intent.

Using an intent is as simple as constructing the Intent with the correct parameters and then invoking that intent using the startActivity method:

public void launchComposeView() {
  // first parameter is the context, second is the class of the activity to launch
  Intent i = new Intent(this, ActivityTwo.class);
  startActivity(i); // brings up the second activity
}

Passing Data Between Activities

In addition to specifying the activity that we want to display, an intent can also pass key-value data between activities. Think of this as specifying the "request parameters" for an HTTP Request. You can specify the parameters by putting key-value pairs into the intent bundle:

public void launchComposeView() {
  // first parameter is the context, second is the class of the activity to launch
  Intent i = new Intent(this, ActivityTwo.class);
  // put "extras" into the bundle for access in the second activity
  i.putExtra("username", "foobar"); 
  i.putExtra("in_reply_to", "george"); 
  i.putExtra("code", 400);
  // brings up the second activity
  startActivity(i); 
}

Once you have added data into the bundle, you can easily access that data within the launched activity:

// ActivityTwo (subactivity) can access any data passed into the inten
String username = getIntent().getStringExtra("username");
String inReplyTo = getIntent().getStringExtra("in_reply_to");
int code = getIntent().getIntExtra("code");

And using this system the intent can pass useful data across activities.

References

• http://developer.android.com/guide/components/intents-filters.html
• http://developer.android.com/reference/android/content/Intent.html
• http://www.vogella.com/articles/AndroidIntent/article.html
• Common Implicit Intents