course on Kotlin Android App Development, appcompat library – Resolving API Compatibility

Hello! Today we will take a detailed look at the AppCompat library, which is essential for Android app development using Kotlin. Maintaining compatibility across devices with different API levels is a very important task when developing Android apps, and we will discuss how to use the AppCompat library as a solution for this.

1. What is the AppCompat library?

The AppCompat library is a library that supports the use of the latest Android features on older Android devices. This allows developers to provide a consistent UI and UX across a variety of devices and API levels. In particular, it makes UI development much easier by allowing the use of various views and themes compatible with Material Design.

2. Why use AppCompat?

Supporting various API levels of Android is becoming increasingly difficult. New UI components introduced from API 21 (Lollipop) are not supported in previous versions. However, by using AppCompat, these components can be utilized in older versions as well. This provides several benefits:

  • API Compatibility: Development can be done using the same code across various devices.
  • Consistent UI Delivery: A consistent user experience is provided across different Android versions.
  • Lightweight Code Maintenance: Reduces code duplication with previous versions, making maintenance easier.

3. Adding AppCompat Dependency

To use the AppCompat library, you need to add the library to your project. To do this, add the following dependency in the build.gradle file:

dependencies {
    implementation 'androidx.appcompat:appcompat:1.3.0'
}

After adding the dependency, you must sync Gradle to include the library in your project.

4. Difference between AppCompatActivity and Basic Activity

The reason you should inherit from AppCompatActivity when creating an Activity in Android is that this class supports the latest UI components and Material Design. By using AppCompatActivity instead of the basic Activity, you can implement functionalities like UIColor, Toolbar, etc., more easily. Here is a simple comparison of the two classes:

import androidx.appcompat.app.AppCompatActivity

class MyActivity : AppCompatActivity() {
    // ...
}

5. Using Toolbar

Toolbar is a commonly used UI element in Android apps, replacing the app’s action bar. When using AppCompatActivity, setting up the Toolbar is done as follows:

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.appcompat.widget.Toolbar

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

        val toolbar: Toolbar = findViewById(R.id.toolbar)
        setSupportActionBar(toolbar)
    }
}

In the above code, setSupportActionBar is used to set the custom Toolbar as the action bar. You need to define the Toolbar in the layout XML and customize the ID.

6. Setting up Theme and Styles

To maintain a consistent overall design for the app, themes and styles need to be set. Using AppCompat, you can define the styles of various UI elements through themes. This can be set in the res/values/styles.xml file as follows:

<resources>
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>
</resources>

The configured theme can be applied throughout the app by specifying it in the AndroidManifest.xml file:

<application
    android:theme="@style/AppTheme">
    ...
</application>

7. Using Dialog

By using the AppCompat library, it’s easy to create Dialogs that comply with Material Design. Here is an example of creating a simple AlertDialog:

import androidx.appcompat.app.AlertDialog

private fun showDialog() {
    AlertDialog.Builder(this)
        .setTitle("Title")
        .setMessage("Message content")
        .setPositiveButton("OK") { dialog, which -> dialog.dismiss() }
        .setNegativeButton("Cancel") { dialog, which -> dialog.cancel() }
        .show()
}

8. Using Fragment

Using Fragment to compose UI in Android apps is common. The AppCompat library supports Fragment, providing flexibility to accommodate various screen sizes and orientations. Here’s how to use a Fragment:

import androidx.fragment.app.Fragment

class MyFragment : Fragment(R.layout.fragment_layout) {
    // Fragment Logic
}

9. RecyclerView and AppCompat

RecyclerView is a powerful item list used to display large amounts of data. The AppCompat library helps to easily integrate with RecyclerView. The basic setup for RecyclerView is as follows:

import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView

class MyActivity : AppCompatActivity() {
    private lateinit var myRecyclerView: RecyclerView

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

        myRecyclerView = findViewById(R.id.my_recycler_view)
        myRecyclerView.layoutManager = LinearLayoutManager(this)
        myRecyclerView.adapter = MyAdapter(dataList)
    }
}

10. Conclusion

Today we learned about the reasons and methods for using the AppCompat library in Android app development utilizing Kotlin. By maintaining compatibility across various APIs and utilizing the latest Android features, AppCompat provides a better user experience. By applying this knowledge to future app development, we hope to provide enjoyable experiences for more devices and diverse users.

References