Repository

https://github.com/enyason/AndroidLauncherApplication

What Will I Learn?

• How to create a custom launcher from scratch
• Enable launcher Mode for our Application
• Implement Home Screen
• Implement App drawer fragment to show all applicationss

Resources

• KISS Launcher source - https://github.com/alexander255/kiss-launcher

Difficulty

• Intermediate

Tutorial Duration - 35 - 40Mins

Tutorial Content

Today I begin a new tutorial series on how to create a custom android launcher from scratch using android studio. 

Launcher is the name given to the part of the Android user interface that lets users customize the home screen (e.g. the phone's desktop), launch mobile apps, make phone calls, and perform other tasks on Android devices (devices that use the Android mobile operating system). source. With this in mind , we will move right away into building a launcher application with the behaviours stated above.

In today's tutorial, we will implement the following features

1. Enable launcher Mode for our Application
2. Implement Home Screen with a Home Button
3. Implement App drawer fragment to show all applications

STEP  1 : Create a New Project

Create a new project and select empty activity to get started

STEP  2 : Enable Launcher Mode

To make our app act and behave like an android launcher, we will add some attributes to the main activity in our manifest file. 

<activity 
    android:name=".MainActivity"
    android:launchMode="singleTask"
    android:theme="@style/AppTheme"
    android:clearTaskOnLaunch="true"
    android:stateNotNeeded="true"
    >

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

        <category android:name="android.intent.category.LAUNCHER" />

        <category android:name="android.intent.category.HOME" />

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

    </intent-filter>

</activity>

code explanation

• The categories   android.intent.category.HOME and android.intent.category.DEFAULT will cause our application to behave like a launcher. So whenever we click on the home button, it is listed out as one of the launchers available .
• The launch mode is set to single task to make sure that only one instance of this Activity is held by the system at any time

With the above steps implemented, our app should behave like shown in the image below

Implement Home Screen And Apps Drawer Screen With Fragment

To implement the Home and apps drawer screen, we will create two fragments which will be contained in our MainActivity.

STEP  3 : Create A fragment Container in  MainActivity Layout

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout

   xmlns:android="http://schemas.android.com/apk/res/android" 
   xmlns:app="http://schemas.android.com/apk/res-auto" 
   xmlns:tools="http://schemas.android.com/tools" 
   android:layout_width="match_parent"

   android:layout_height="match_parent"
 tools:context="com.nexdev.enyason.androidlauncherapplication.MainActivity">
   <FrameLayout

       android:layout_width="match_parent"
       android:id="@+id/container"
       android:layout_height="match_parent"></FrameLayout>

</RelativeLayout>

code explanation

The FrameLayout in the code block above will serve as a container for any fragment being loaded into the MainActivity

STEP  3 : Create Fragment for Home Screen

XML Layout code 

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

   tools:context="com.nexdev.enyason.androidlauncherapplication.MainActivity">

    <ImageView

        android:id="@+id/icon_drawer"

        android:layout_marginBottom="20dp"

        android:layout_centerInParent="true"

        android:layout_alignParentBottom="true"

        android:src="@drawable/ic_apps"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content" />

</RelativeLayout>

The image view displays the home button icon that provides access to the Apps Drawer Screen

Java  code 

public class HomeScreenFragment extends Fragment {

    public HomeScreenFragment() {}

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.fragment_home_screen,container,false);
        return view;
    }
}

complete source code

The Home Screen XML layout created at the beginning of STEP 3 is inflated and returned as a view in the onCreateView method of the HomeScreenFragment

STEP  4 : Create Fragment for Apps Drawer

XML Layout code 

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

   tools:context="com.nexdev.enyason.androidlauncherapplication.MainActivity">

    <android.support.v7.widget.CardView

        app:cardBackgroundColor="#FFF"

        android:layout_width="match_parent"

        android:layout_height="match_parent">



        <RelativeLayout

            android:layout_width="match_parent"

            android:layout_height="match_parent">

            <TextView

                android:textColor="#000"

                android:textStyle="bold"

                android:layout_centerInParent="true"

                android:text="Apps Drawer"

                android:layout_width="wrap_content"

                android:layout_height="wrap_content" />

        </RelativeLayout>

    </android.support.v7.widget.CardView>



</RelativeLayout>

Java  code 

public class AppsDrawerFragment extends Fragment {

    public AppsDrawerFragment() {}

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.fragment_apps_drawer,container,false);
        return view;
    }

}

STEP 5 : Attach Fragment to MainActivity

In the onCreate menu of the MainActivity, load the HomeScreenFragment 

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        loadFragment(new HomeScreenFragment());

    }

    private boolean loadFragment(Fragment fragment) {

        if (fragment != null) {

            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.container, fragment)
                    .commit();
            return true;

        }

        return false;

    }

}

code explanation

• The loadFragment method takes an instance of the HomeScreenFragment  and attach it to the MainActivity, with it's FrameLayout serving as a containing view for the fragment's layout.
  

With Steps 3,4 & 5 done, our app should look like this : 

Implement  show all applications Feature in The Drawer Screen

STEP 6 :  Create A Java Class with Application Info Attributes

public class AppInfo  {

    CharSequence label;
    CharSequence packageName;
    Drawable icon;
}

STEP 6 :  Create a custom Adapter Class that extends the RecyclerView Adapter Class

In the constructor of our custom adapter, we are going to fetch the app list from the phone with all its attribute

public class AppsDrawerAdapter extends RecyclerView.Adapter<AppsDrawerAdapter.ViewHolder> {

    private static Context context;
    private static List<AppInfo> appsList;
    public AppsDrawerAdapter(Context c ) {
        context = c;
        setUpApps();
    }
   public static void setUpApps(){
       PackageManager pManager = context.getPackageManager();

         appsList = new ArrayList<AppInfo>();
        Intent i = new Intent(Intent.ACTION_MAIN, null);
        i.addCategory(Intent.CATEGORY_LAUNCHER);
        List<ResolveInfo> allApps = pManager.queryIntentActivities(i, 0);

        for (ResolveInfo ri : allApps) {
            AppInfo app = new AppInfo();
            app.label = ri.loadLabel(pManager);
            app.packageName = ri.activityInfo.packageName;

            Log.i(" Log package ",app.packageName.toString());
            app.icon = ri.activityInfo.loadIcon(pManager);
            appsList.add(app);

        }

    }

}

complete source code

code explanation

• The AppsDrawerAdapter constructor requires a context from the application, which will be used to get the Package Manager.
• In the setUpApps method of the AppsDrawerAdapter class, we use the queryIntentActivities method of the PackageManager class to fetch all the Intents that have a category of Intent.CATEGORY_LAUNCHER. The query returns a list of the applications that can be launched by a launcher.
•  We use a For loop to Loop through the results of the query and add each item to a list named appsList.

STEP 6 : Display The List of Applications in the Apps Drawer Screen

With our List of installed apps available, we can now display it in our Apps Drawer Screen using a recyclerView. Include the following code to the AppDrawer Fragment Class

@Override

public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    recyclerView = view.findViewById(R.id.appDrawer_recylerView);
    adapter = new AppsDrawerAdapter(getContext());
    layoutManager = new LinearLayoutManager(getContext());
     recyclerView.setLayoutManager(layoutManager);
    recyclerView.setAdapter(adapter);

}

complete source code

STEP 7 : Test The Application 

Application Demo - With these steps covered, our app should look like this

Proof of Work Done  

The complete source code can be found on github 

https://github.com/enyason/AndroidLauncherApplication