Intents

Intent Overview

An Intent is a messaging object used for communication between different components of an Android application. It serves three fundamental use cases:

Hpw Intents Works

1. Starting an Activity:

   • Represents a single screen in an app.

   • New instances are started by passing an Intent to startActivity().

   • startActivityForResult() is used for receiving results from the activity.

2. Starting a Service:

   • A background component performing operations without a user interface.

   • Started using startService() for one-time operations.

   • bindService() is used for a client-server interface interaction.

3. Delivering a Broadcast:

   • A message that any app can receive.

   • System delivers broadcasts for various events.

   • Delivered using sendBroadcast() or sendOrderedBroadcast().

Intent Types

Explicit Intents

• Specify the exact component (activity or service) that will satisfy the intent.

• Uses a full ComponentName or Package Name to specify the target.

• Typically used for starting components within the same app.

// Explicit Intent to start another activity within the same app
Intent explicitIntent = new Intent(CurrentActivity.this, TargetActivity.class);
explicitIntent.putExtra("key", "value"); // Optional: Adding extra data
startActivity(explicitIntent);

Implicit Intents

• Do not specify a specific component but declare a general action to perform.

• Allow components from other apps to handle the intent.

• Used when the exact component is unknown or when interacting with other apps.

// Implicit Intent to open a webpage using a browser
String url = "https://www.example.com";
Intent implicitIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
startActivity(implicitIntent);

Intent Components

1. Name:

   • Definition: The name of the component (activity, service) that the intent is targeting.

   • Usage: In explicit intents, specifies the exact component to be invoked.

2. Action:

   • Definition: Describes the requested action to be performed by the targeted component.

   • Usage: Specifies the type of operation, such as viewing, sending, or opening.

3. Data:

   • Definition: Represents the data to be operated upon by the targeted component.

   • Usage: Contains a URI or data type that helps define the context of the action.

4. Category:

   • Definition: Describes additional information about the kind of component that should handle the intent.

   • Usage: Categorizes the intent for better filtering by the system.

5. Extras:

   • Definition: Carries additional key-value pairs providing extended information.

   • Usage: Used for passing extra data between components, enhancing the intent's payload.

Intent Filters

• Definition: Expressions in an app's manifest file specifying the type of intents a component would like to receive.

• Use Cases:

  • Declaring an intent filter for an activity allows other apps to directly start that activity.

  • Components without intent filters can only be started with explicit intents.

Notes on Intent Filters and android:exported Attribute

• android:exported Attribute:

  • Set explicitly in each app component's <intent-filter> element.

  • Indicates the accessibility of the app component to other apps.

  • For activities with LAUNCHER category, set to true; otherwise, set to false for safety.

  • Warning: Android 12 or higher requires explicit setting; failure may result in app installation issues.

• Elements:

  • Specify the type of intents accepted within the <intent-filter> using three elements:

    • <action>: Declares the accepted intent action.

    • <data>: Declares the accepted data type, specifying URI aspects and MIME type.

    • <category>: Declares the accepted intent category.

• Implicit Intents and CATEGORY_DEFAULT:

  • To receive implicit intents, include the CATEGORY_DEFAULT category in the intent filter.

  • startActivity() and startActivityForResult() treat all intents as if they have CATEGORY_DEFAULT.

  • Failure to declare this category results in no resolution for implicit intents.

• Example:

  • Activity declaration with an intent filter to receive ACTION_SEND intent with text MIME type:

    <activity android:name="ShareActivity" android:exported="false">
        <intent-filter>
            <action android:name="android.intent.action.SEND"/>
            <category android:name="android.intent.category.DEFAULT"/>
            <data android:mimeType="text/plain"/>
        </intent-filter>
    </activity>

Understanding intent filters, the android:exported attribute, and proper declaration is crucial for secure and effective communication between Android app components.