How to Create a Simple Launcher App for Android

1. we need make this app as home launcher. Bind the HOME key press.

When you click the HOME key. This selector shows up.

55_2_48be3591a12df52 Add two category to AndroidManifest.xml

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

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

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.son1c.launcher"
      android:versionCode="1"
      android:versionName="1.0">
      
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MainActivity"
                  android:label="@string/app_name"></application>
                  
            <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>

2. List all apps in Android

Most launders is used to list apps.

55_2_3b434ff967012d6

1) Modify main.xml and add GridView to it. 
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <GridView android:layout_width="match_parent"
        android:id="@+id/apps_list"
        android:numColumns="4"
        android:layout_height="wrap_content">
2) Search all the apps by PackageManager 
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private void loadApps() {
    Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
    mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);

    mApps = getPackageManager().queryIntentActivities(mainIntent, 0);
}
3) Add adapter for GridView 
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public class AppsAdapter extends BaseAdapter {

        public AppsAdapter() {
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView i;
            if (convertView == null) {
                i = new ImageView(MyHome.this);
                i.setScaleType(ImageView.ScaleType.FIT_CENTER);
                i.setLayoutParams(new GridView.LayoutParams(50, 50));
            } else {
                i = (ImageView) convertView;
            }
            ResolveInfo info = mApps.get(position);
            i.setImageDrawable(info.activityInfo.loadIcon(getPackageManager()));

            return i;
        }

        public final int getCount() {
            return mApps.size();
        }

        public final Object getItem(int position) {
            return mApps.get(position);
        }

        public final long getItemId(int position) {
            return position;
        }
}
4) Add onItemClick for GridView 
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private OnItemClickListener listener = new OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,long id) {
        //TODO....
    }
};
5) Launch app when click 
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public void onItemClick(AdapterView<?> parent, View view, int position,long id) {
            ResolveInfo info = mApps.get(position);
            // Package Name
            String pkg = info.activityInfo.packageName;
            // Main activity of app
            String cls = info.activityInfo.name;

            ComponentName componet = new ComponentName(pkg, cls);

            Intent i = new Intent();
            i.setComponent(componet);
            startActivity(i);
        }
}
6) Disable the BACK key 
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public boolean onKeyDown(int keyCode, KeyEvent event) {
	if (keyCode == KeyEvent.KEYCODE_BACK) {
		return true;
	} else {
		return super.onKeyDown(keyCode, event);
	}
}
Finally the whole Activity code: 
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package com.son1c.launcher;

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.pm.ResolveInfo;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class MainActivity extends Activity {

	private List<resolveinfo> mApps;
	private GridView mGrid;
	private OnItemClickListener listener = new OnItemClickListener() {
		@Override
		public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
			ResolveInfo info = mApps.get(position);
			String pkg = info.activityInfo.packageName;
			String cls = info.activityInfo.name;
			ComponentName componet = new ComponentName(pkg, cls);</resolveinfo>

			Intent i = new Intent();
			i.setComponent(componet);
			startActivity(i);
		}

	};

	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);

		loadApps();
		setContentView(R.layout.main);
		mGrid = (GridView) findViewById(R.id.apps_list);
		mGrid.setAdapter(new AppsAdapter());

		mGrid.setOnItemClickListener(listener);
	}

	private void loadApps() {
		Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
		mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);

		mApps = getPackageManager().queryIntentActivities(mainIntent, 0);
	}

	public class AppsAdapter extends BaseAdapter {
		public AppsAdapter() {
		}

		public View getView(int position, View convertView, ViewGroup parent) {
			ImageView i;

			if (convertView == null) {
				i = new ImageView(MainActivity.this);
				i.setScaleType(ImageView.ScaleType.FIT_CENTER);
				i.setLayoutParams(new GridView.LayoutParams(120, 120));
				i.setPadding(12, 12, 12, 12);
			} else {
				i = (ImageView) convertView;
			}

			ResolveInfo info = mApps.get(position);
			i.setImageDrawable(info.activityInfo.loadIcon(getPackageManager()));

			return i;
		}

		public final int getCount() {
			return mApps.size();
		}

		public final Object getItem(int position) {
			return mApps.get(position);
		}

		public final long getItemId(int position) {
			return position;
		}
	}

	@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {
		if (keyCode == KeyEvent.KEYCODE_BACK) {
			return true;
		} else {
			return super.onKeyDown(keyCode, event);
		}
	}
}