Allow-Other-Apps-to-Start-Your-Activity

This Tutorial will discuss how to allow other applications to start your application and how you could benefit from this behavior.

This Tutorial discusses the following:

Why should I allow other Apps to open my App ?
What is Intent & Intent-Filter ?
Understand How Android System Deals with Implicit Intents
Allow Other Apps To Open A Certain Activity in Your App
Available Actions, Categories, Data Types

This is a part of Android App Links Series.

Why Allowing Other Apps to start my App

The first question that should come up on your mind is Why should I allow other apps to open my App.

As an answer for this question, Allowing other apps to open your app actually benefits you more that the other app. Because it simply redirects users to your app and increases user engagement with your app. It also make it easier for the user himself to use your app. For Example, if you allow "Share Action" to your app, The user could simply grab a content from other apps (such as Facebook, gallery, ... whatever) by pressing the share button and post it in your app instead of writing the content again in your app.

Intent & Intent-Filter

The main concept behind allowing other apps to open your app is the Intent & Intent-Filter. If you are asking what does it mean, Here is a snippet from the Official Android Documentation about the Intent "Its most significant use is in the launching of activities, where it can be thought of as the glue between activities. It is basically a passive data structure holding an abstract description of an action to be performed"

https://developer.android.com/reference/android/content/Intent

So, The Intent is the main method to start an Activity which exactly what the other app will need to do "Start your App's Activity".

There is Two types of intents: Explicit & Implicit. The Explicit Intent is the one you are using inside your app to navigate from one activity to another as you know the exact class name that you want to go to. The Implicit Intent is where you don't know the exact class name of your destination OR you don't mind any destination as long as it will perform the requested action, here comes the Intent-Filter.

The Intent Filter is the way that the activity identifies itself to the Android System. So, If the activity, for example, is used to share a post in a social app, This Activity will identify itself by saying "Hey, I can handle a Share Action" or in more technical terms it will declare an Action_SEND in its manifest file.

So, If you want other apps to use your activities, You should declare what kind of actions that your activities could handle in your manifest file using the Intent-Filter. You could also specify the kind of data that your activity expect to receive.

Understand How Android System Deals with Implicit Intents

When some app makes an Implicit Intent, The Android System will scan all the Installed Applications and search in their Manifest Files for any Activity that could handle this specific action, category, and data type that is send along with the Implicit Intent by querying the PackageManager. Once the Android System finds some matching activities, Android System shows these activities in a Dialog so the user could choose the desired activity. If there is Only One Activity that could handle this action, Android System will automatically opens it. If no activity has been found, The Android System will return null to the requested app.

As We are in The Android App Links Series, It is worthy to be mentioned that

Here is one major difference between the Deep Link and Android App Link. If you are using a deep link, Android System will show the dialog mentioned in the above paragraph. If you are using Android App Link, The Android System will automatically opens your app showing this dialog.

Allow Other Apps To Open A Certain Activity in Your App

Step One: Add Intent Filters from Incoming Intents

First, allow other apps find & open a certain activity in your app by doing the following steps:

Declare an <intent-filter> inside your <activity> tag in the manifest file.
Specify the kind of <action> that your activity could handle.
Specify the kind of <category> that your activity could handle.
Specify the kind of <data> that your activity expects.

Here is a code snippet for an activity allowing a Send Action

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

If your are trying to create Deep Links, Consider using the <data> tag to declare a scheme and host. So That your app could be reached by URLs.

Some Important Notes About <intent-filter> :

1. Intent Filters will allow all possible combinations of your declared actions, categories, data type.

In Other Words, If you declared ACTION_SEND, ACTION_VIEW, CATEGORY_DEFAULT, CATEGORY_BROWSABLE, scheme = http, scheme = https. This Means Your are allowing all of the following intents:

Intent declares ACTION_SEND with CATEGORY_DEFAULT and scheme = http
Intent declares ACTION_SEND with CATEGORY_DEFAULT and scheme = https
Intent declares ACTION_SEND with CATEGORY_BROWSABLE and scheme = http
Intent declares ACTION_SEND with CATEGORY_BROWSABLE and scheme = https
Intent declares ACTION_VIEW with CATEGORY_DEFAULT and scheme = http
Intent declares ACTION_VIEW with CATEGORY_DEFAULT and scheme = https
Intent declares ACTION_VIEW with CATEGORY_BROWSABLE and scheme = http
Intent declares ACTION_VIEW with CATEGORY_BROWSABLE and scheme = https

OR any intent declaring at least one ore more from the above declaration

     <intent-filter>
         <action android:name="android.intent.action.SEND" />
         <action android:name="android.intent.action.VIEW" />

         <category android:name="android.intent.category.DEFAULT" />
         <category android:name="android.intent.category.BROWSABLE" />

         <data android:mimeType="http" />
         <data android:scheme="https" />
     </intent-filter>

2. If you want to restrict intents to certain combinations of action, category, data type, You have to considered using multiple <intent-filter>

In Other Words, If you declared two <intent-filter> tags, The first one has ACTION_SEND, CATEGORY_DEFAULT, scheme = http and The second one has ACTION_VIEW, CATEGORY_BROWSABLE, scheme = https. This Means Your are allowing only the following intents:

Intent declares ACTION_SEND with CATEGORY_DEFAULT and scheme = http
Intent declares ACTION_VIEW with CATEGORY_BROWSABLE and scheme = https

OR any intent declaring at least one ore more from the above declaration

     <intent-filter>
         <action android:name="android.intent.action.SEND" />
         <category android:name="android.intent.category.DEFAULT" />
         <data android:mimeType="http" />
     </intent-filter>
     
     <intent-filter>
         <action android:name="android.intent.action.VIEW" />
         <category android:name="android.intent.category.BROWSABLE" />
         <data android:scheme="https" />
     </intent-filter>

3. If you intent to use ACTION_VIEW, you have to scpecify a CATEGORY_BROWSABLE and a URL by declaring a <data> tag with at least a scheme attribute.

        <intent-filter >
            <action android:name="android.intent.action.VIEW" />
            <category android:name="android.intent.category.BROWSABLE" />
            <data android:scheme="https" />
        </intent-filter>

4. Intent Filters will allow all possible combinations of your data tag attributes.

In Other Words, If you declared <data> tag with scheme = http, host = www.example.com and another <data> tag with scheme = app, host = your.app.name . This Means Your are allowing all of the following URLs:

http://www.example.com
app://www.example.com
http://your.app.name

app://your.app.name

     <intent-filter>
         ...
         <data android:scheme="http" android:host="www.example.com" />
         <data android:scheme="app" android:host="your.app.name" />
     </intent-filter>

5. If you want to restrict intents to certain combinations of data tag attributes, You have to considered using multiple <intent-filter>

In Other Words, If you declared two <intent-filter> tags, The first one has <data> tag with scheme = http, host = www.example.com and The second one has <data> tag with scheme = app, host = your.app.name . This Means Your are allowing only the following URLs:

http://www.example.com

app://your.app.name

     <intent-filter>
         ...
         <data
             android:host="www.example.com"
             android:scheme="http" />
     </intent-filter>
     <intent-filter>
         ...
         <data
             android:host="your.app.name"
             android:scheme="app" />
     </intent-filter>

Step Two: Read From Incoming Intent

Second, prepare your activity to receive the data sent by other app through the intent by doing the following steps:

Get a reference of the intent
Get the action sent along with the intent. You could ignore this if your activity receives only one action.
Get the data type sent along with the intent by calling getType() on the intent reference.
Get the data sent along with the intent by calling getExtra() on the intent reference.
Perform your custom business logic to show or deal with the data received to meet the user's expectations

Here is a code snippet for an activity allowing more than one Action, This snippet has been taken from Android Documentation

https://developer.android.com/training/sharing/receive

     @Override
     public void onCreate(Bundle savedInstanceState) {
        ...
        // Get intent, action and MIME type
        Intent intent = getIntent();
        String action = intent.getAction();
        String type = intent.getType();

        if (Intent.ACTION_SEND.equals(action) && type != null) {
            if ("text/plain".equals(type)) {
                handleSendText(intent); // Handle text being sent
            } else if (type.startsWith("image/")) {
                handleSendImage(intent); // Handle single image being sent
            }
        } else if (Intent.ACTION_SEND_MULTIPLE.equals(action) && type != null) {
            if (type.startsWith("image/")) {
                handleSendMultipleImages(intent); // Handle multiple images being sent
            }
        } else {
            // Handle other intents, such as being started from the home screen
        }
        ...
    }

    private void handleSendText(Intent intent) {
        String sharedText = intent.getStringExtra(Intent.EXTRA_TEXT);
        if (sharedText != null) {
            // Update UI to reflect text being shared
        }
    }

    private void handleSendImage(Intent intent) {
        Uri imageUri = (Uri) intent.getParcelableExtra(Intent.EXTRA_STREAM);
        if (imageUri != null) {
            // Update UI to reflect image being shared
        }
    }

    private void handleSendMultipleImages(Intent intent) {
        ArrayList<Uri> imageUris = intent.getParcelableArrayListExtra(Intent.EXTRA_STREAM);
        if (imageUris != null) {
            // Update UI to reflect multiple images being shared
        }
    }

Here is a list of available intent actions, categories, data types

Intent Actions

android.intent.action.ALL_APPS
android.intent.action.ANSWER
android.intent.action.APPLICATION_PREFERENCES
android.intent.action.APP_ERROR
android.intent.action.ASSIST
android.intent.action.ATTACH_DATA
android.intent.action.BUG_REPORT
android.intent.action.CALL
android.intent.action.CALL_BUTTON
android.intent.action.CALL_EMERGENCY
android.intent.action.CALL_PRIVILEGED
android.intent.action.CARRIER_SETUP
android.intent.action.CHOOSER
android.intent.action.CREATE_DOCUMENT
android.intent.action.CREATE_LIVE_FOLDER
android.intent.action.CREATE_SHORTCUT
android.intent.action.DELETE
android.intent.action.DIAL
android.intent.action.DISMISS_ALARM
android.intent.action.DISMISS_TIMER
android.intent.action.EDIT
android.intent.action.EVENT_REMINDER
android.intent.action.FACTORY_TEST
android.intent.action.GET_CONTENT
android.intent.action.INSERT
android.intent.action.INSERT_OR_EDIT
android.intent.action.INSTALL_FAILURE
android.intent.action.INSTALL_INSTANT_APP_PACKAGE
android.intent.action.INSTALL_PACKAGE
android.intent.action.INSTANT_APP_RESOLVER_SETTINGS
android.intent.action.MAIN
android.intent.action.MANAGE_APP_PERMISSIONS
android.intent.action.MANAGE_NETWORK_USAGE
android.intent.action.MANAGE_PERMISSIONS
android.intent.action.MANAGE_PERMISSION_APPS
android.intent.action.MEDIA_SEARCH
android.intent.action.MUSIC_PLAYER
android.intent.action.OPEN_DOCUMENT
android.intent.action.OPEN_DOCUMENT_TREE
android.intent.action.PASTE
android.intent.action.PICK
android.intent.action.PICK_ACTIVITY
android.intent.action.POWER_USAGE_SUMMARY
android.intent.action.PROCESS_TEXT
android.intent.action.QUICK_VIEW
android.intent.action.REVIEW_PERMISSIONS
android.intent.action.RINGTONE_PICKER
android.intent.action.RUN
android.intent.action.SEARCH
android.intent.action.SEARCH_LONG_PRESS
android.intent.action.SEND
android.intent.action.SENDTO
android.intent.action.SEND_MULTIPLE
android.intent.action.SET_ALARM
android.intent.action.SET_TIMER
android.intent.action.SET_WALLPAPER
android.intent.action.SHOW_ALARMS
android.intent.action.SHOW_APP_INFO
android.intent.action.SHOW_SUSPENDED_APP_DETAILS
android.intent.action.SHOW_TIMERS
android.intent.action.SNOOZE_ALARM
android.intent.action.SYNC
android.intent.action.SYSTEM_TUTORIAL
android.intent.action.UNINSTALL_PACKAGE
android.intent.action.UPGRADE_SETUP
android.intent.action.VIEW
android.intent.action.VIEW_DOWNLOADS
android.intent.action.VOICE_ASSIST
android.intent.action.VOICE_COMMAND
android.intent.action.WEB_SEARCH

Intent Data Types

audio/audioType, you could use * as subtype to indicate that all audio types are acceptable
video/videoType, you could use * as subtype to indicate that all video types are acceptable
image/imageType, you could use * as subtype to indicate that all image types are acceptable
text/textType, you could use * as subtype to indicate that all text types are acceptable
application/otherTypes
*/*, you could use / to indicate that all media types are acceptable