Build a simple Android laucher

[Jasmine-liang]

What it looks like

[Jasmine-liang]

Challenge from Android Programming: The Big Nerd Ranch Guild, 4th Edition

Show also icons in RecyclerView.

Chapter 23

Steps to consider to make a laucher:

• Find launchable activities which are simply activities with intent filters that include a MAIN actionand a LAUNCHER category
• Create an implicit intent and get a list of activities that match the intent from PackageManager
• Query the activities through PackageManager.queryIntentActivities and get a list containing ResolveInfo object, which contains lables, along with other metadata like icon in it
• Create a explicit intent to start the selected activity

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Code

MainActivity.kt

import android.content.Intent
import android.content.pm.ResolveInfo
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
private const val TAG = "MainActivity"
class MainActivity : AppCompatActivity() {

    private lateinit var recyclerView: RecyclerView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        recyclerView = findViewById(R.id.app_recycler_view)
        recyclerView.layoutManager = LinearLayoutManager(this)
        setupAdapter()
    }

    private fun setupAdapter() {
        val startupIntent = Intent(Intent.ACTION_MAIN).apply {
            addCategory(Intent.CATEGORY_LAUNCHER)
        }

        val packageManager = packageManager
        val activities = packageManager.queryIntentActivities(startupIntent, 0)
        activities.sortWith { a, b ->
            String.CASE_INSENSITIVE_ORDER.compare(
                a.loadLabel(packageManager).toString(),
                b.loadLabel(packageManager).toString()
            )
        }
        recyclerView.adapter = ActivityAdapter(activities)
    }

    private  class ActivityHolder(itemView: View) :
            RecyclerView.ViewHolder(itemView),
            View.OnClickListener {

        val appIcon: ImageView = itemView.findViewById(R.id.app_icon)
        val appName: TextView = itemView.findViewById(R.id.app_name)
        private lateinit var resolveInfo: ResolveInfo

        init {
           itemView.setOnClickListener(this)
        }

        fun bindActivity(resolveInfo: ResolveInfo) {
            this.resolveInfo = resolveInfo
            val packageManager = itemView.context.packageManager
            appName.text = resolveInfo.loadLabel(packageManager).toString()
            appIcon.setImageDrawable(resolveInfo.loadIcon(packageManager))

        }

        override fun onClick(view: View) {
            val activityInfo = resolveInfo.activityInfo

            val intent = Intent(Intent.ACTION_MAIN).apply {
                setClassName(activityInfo.applicationInfo.packageName,
                        activityInfo.name)
                addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
            }

            val context = view.context
            context.startActivity(intent)
        }
    }

    private class ActivityAdapter(val activities: List<ResolveInfo>) :
            RecyclerView.Adapter<ActivityHolder>() {

        override fun onCreateViewHolder(container: ViewGroup, viewType: Int):
                ActivityHolder {
            val layoutInflater = LayoutInflater.from(container.context)
            val view = layoutInflater
                    .inflate(R.layout.list_of_apps, container, false)

            return ActivityHolder(view)
        }

        override fun onBindViewHolder(holder: ActivityHolder, position: Int) {
            val resolveInfo = activities[position]
            holder.bindActivity(resolveInfo)
        }

        override fun getItemCount(): Int {
            return activities.size
        }
    }
}

[Jasmine-liang]

_list_of_apps.xml_

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
    android:orientation="horizontal"
    android:gravity="center_vertical"
    android:padding="8dp"
    android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/app_icon"
        android:src="@drawable/abc_vector_test"
        android:layout_width="80dp"
        android:layout_marginRight="10dp"
        android:layout_marginTop="10dp"
        android:layout_height="80dp"/>
    <TextView
        android:id="@+id/app_name"
        android:text="app"
        android:textSize="20sp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</LinearLayout>

---

_activity_main.xml_

<?xml version="1.0" encoding="utf-8"?>
<androidx.recyclerview.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/app_recycler_view"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"/>