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Seyeon

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[Kotlin] Application Resources and Building User Interfaces

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📋 Here are the notes summarizing what I learned from the course!


Application Resources and Building User Interfaces

Objectives:

  • Explain Android activities, fragments, and intents.
  • Understand application, activity, and fragment life cycles.
  • Create and use activities.
  • Apply intents to call built-in applications and pass information to other activities.
  • Create and use fragments.

Activities

Definition

  • Activity: An application component that provides a screen for user interaction to do things like dialing the phone, taking a photo, sending an email, or viewing a map. Each activity is given a window to draw its user interface.

Creating an Activity

  • To create an activity, create a subclass of Activity or AppCompatActivity for compatibility support.
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

Registering an Activity in the Manifest

  • Activities need to be registered in the Android manifest with necessary metadata like labels and themes.
<activity android:name=".MainActivity">
    <intent-filter>
        <action android:name="android.intent.action.MAIN"/>
        <category android:name="android.intent.category.LAUNCHER"/>
    </intent-filter>
</activity>

Using AppCompatActivity

  • AppCompatActivity provides backward compatibility for features added in newer releases of the Android platform.
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }
}

Activity States and Lifecycle Callbacks

Lifecycle States

  • Nonexistent
  • Created
  • Started
  • Resumed
  • Destroyed

Example: Lifecycle Callbacks

  • Lifecycle methods like onCreate, onStart, onResume, onPause, onStop, and onDestroy handle transitions between states.
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Log.d(TAG, "onCreate(Bundle?) called")
    }

    override fun onStart() {
        super.onStart()
        Log.d(TAG, "onStart() called")
    }

    override fun onResume() {
        super.onResume()
        Log.d(TAG, "onResume() called")
    }

    override fun onPause() {
        super.onPause()
        Log.d(TAG, "onPause() called")
    }

    override fun onStop() {
        super.onStop()
        Log.d(TAG, "onStop() called")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d(TAG, "onDestroy() called")
    }
}

Managing Activity Transitions with Intents

Intents

  • Intents are asynchronous messages used to request an action from another app component.

Example: Starting an Activity

val intent = Intent(this, ActivityB::class.java)
startActivity(intent)

Passing Data with Intents

val intent = Intent(this, DisplayMessageActivity::class.java)
intent.putExtra("EXTRA_MESSAGE", "Hello World!")
startActivity(intent)

Fragments

Definition

  • Fragment: A modular section of an activity, which has its own lifecycle and can be added or removed while the activity is running.

Example: Creating a Fragment

class AboutFragment : Fragment() {
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment_about, container, false)
    }
}

Fragment Lifecycle

States

  • Fragments transition through various states in their lifecycle, similar to activities.

Example: Fragment Lifecycle Callbacks

class AboutFragment : Fragment() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Log.d(TAG, "onCreate(Bundle?) called")
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        Log.d(TAG, "onCreateView() called")
        return inflater.inflate(R.layout.fragment_about, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        Log.d(TAG, "onActivityCreated() called")
    }

    override fun onStart() {
        super.onStart()
        Log.d(TAG, "onStart() called")
    }

    override fun onResume() {
        super.onResume()
        Log.d(TAG, "onResume() called")
    }

    override fun onPause() {
        super.onPause()
        Log.d(TAG, "onPause() called")
    }

    override fun onStop() {
        super.onStop()
        Log.d(TAG, "onStop() called")
    }

    override fun onDestroyView() {
        super.onDestroyView()
        Log.d(TAG, "onDestroyView() called")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d(TAG, "onDestroy() called")
    }

    override fun onDetach() {
        super.onDetach()
        Log.d(TAG, "onDetach() called")
    }
}

Adding and Managing Fragments

Example: Adding a Fragment to an Activity

<FragmentContainerView
    android:id="@+id/fragment_container_view"
    android:name="com.example.android.fragments.AboutFragment"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

Android Manifest File

Definition

  • The Android Manifest File contains application configuration information such as the application’s package name, components (activities, services, broadcast receivers, content providers), permissions, and hardware/software features.

Example: Registering Activities in the Manifest

<activity android:name=".MyActivity" />

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

Example: Using Features and Permissions

<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

Configuring the Gradle Build

Definition

  • Gradle files define your build configuration. They include project-scoped and module-scoped build files.

Example: Adding Dependencies

dependencies {
    implementation 'androidx.recyclerview:recyclerview:1.1.0'
}

Android UI Toolkits

Toolkits

  • Android View System: Resources defined in XML.
  • Jetpack Compose: Declarative API to describe the UI programmatically.

Example: Creating Layouts Using XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, World!" />
</LinearLayout>

RecyclerView

Definition

  • RecyclerView is a ViewGroup for displaying large sets of data efficiently.

Example: Using RecyclerView

<androidx.recyclerview.widget.RecyclerView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" />

Example: Creating a RecyclerView Adapter

class MyRecyclerViewAdapter(private val myDataset: Array<String>) :
    RecyclerView.Adapter<MyRecyclerViewAdapter.MyViewHolder>() {

    class MyViewHolder(val textView: TextView) : RecyclerView.ViewHolder(textView)

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        val textView = LayoutInflater.from(parent.context)
            .inflate(R.layout.text_view, parent, false) as TextView
        return MyViewHolder(textView)
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        holder.textView.text = myDataset[position]
    }

    override fun getItemCount() = myDataset.size
}

Example: Setting up RecyclerView in an Activity

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

        val recyclerView = findViewById<RecyclerView>(R.id.recycler_view)
        recyclerView.layoutManager = LinearLayoutManager(this)
        recyclerView.adapter = MyRecyclerViewAdapter(arrayOf("Item 1", "Item 2", "Item 3"))
    }
}

Declarative Data Binding

Definition

  • The Data Binding library allows you to bind UI components in your layouts to data sources in your app using a declarative format.

Example: Enabling Data Binding

android {
    buildFeatures {
        dataBinding true
    }
}

Example: Using Data Binding in a Layout

<layout xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
        <variable name="user" type="com.example.User" />
    </data>
    <LinearLayout
        android:orientation="vertical"
        android:

layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{user.name}" />
    </LinearLayout>
</layout>

Example: Setting up Data Binding in an Activity

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding: ActivityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main)
        val user = User("John Doe")
        binding.user = user
    }
}

References



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