kotlin android app development course, how to design screens using views

In Android application development, the view is the most fundamental component that makes up the user interface. In this course, we will delve into how to structure the screens of an Android app using Kotlin, and we will explain how to create various layouts with examples using views.

1. Understanding Android Views

The UI of Android applications is composed of various views. A view is a graphical element that allows interaction with the user. The basic types of views used in Android are as follows:

• TextView – A view that displays text
• EditText – A text input view that can receive user input
• Button – A button that handles click events
• ImageView – A view that displays images
• CheckBox – A selectable item
• RadioButton – Mutually exclusive selection items
• RecyclerView – Efficiently displays list items

1.1 The Role and Importance of Views

Views enable interaction between the user and the application, significantly influencing the app’s usability. Using appropriate views and layouts can maximize the user experience. Moreover, views can be combined with other views to create complex UIs.

2. Constructing Layouts

Android provides various types of layouts to determine how to arrange views. The main types of layouts are as follows:

• LinearLayout – Arranges views either horizontally or vertically
• RelativeLayout – Places views based on relative positions to each other
• ConstraintLayout – Flexibly arranges views based on constraints
• FrameLayout – Displays one view on top of another

2.1 LinearLayout Example

Let’s learn how to arrange views using the LinearLayout, one of the most basic layouts, either horizontally or vertically.

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, Kotlin Android!" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click me!" />

</LinearLayout>

2.2 RelativeLayout Example

Let’s look at an example using RelativeLayout, which allows positioning views based on relative locations.

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/relativeTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="RelativeLayout Example"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp" />

    <Button
        android:id="@+id/relativeButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Relative Button"
        android:layout_below="@id/relativeTextView"
        android:layout_centerHorizontal="true" />

</RelativeLayout>

2.3 ConstraintLayout Example

Let’s create a more complex layout using the ConstraintLayout, which is widely used in recent Android development.

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/constraintTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ConstraintLayout Example"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

    <Button
        android:id="@+id/constraintButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Constraint Button"
        app:layout_constraintTop_toBottomOf="@id/constraintTextView"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

3. View Data Binding

Now, let’s explore data binding, which allows for efficient management of the connection between UI elements and data.

3.1 Setting Up Data Binding

To use data binding, you must first enable it in the project’s build.gradle file.

android {
    ...
    buildFeatures {
        dataBinding true
    }
}

3.2 Data Binding Example

Let’s look at a basic example using data binding.

<layout xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
        <variable
            name="viewModel"
            type="com.example.myapplication.MyViewModel" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{viewModel.text}" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="@{() -> viewModel.onButtonClick()}"
            android:text="Button Click" />

    </LinearLayout>
</layout>

4. Managing View States

Managing the state of views is important for enhancing application stability and improving user experience.

4.1 Saving View State

The state of a view can be saved by overriding the onSaveInstanceState() method.

override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)
    outState.putString("text", textView.text.toString())
}

4.2 Restoring View State

The saved state can be restored by overriding the onRestoreInstanceState() method.

override fun onRestoreInstanceState(savedInstanceState: Bundle) {
    super.onRestoreInstanceState(savedInstanceState)
    val savedText = savedInstanceState.getString("text")
    textView.text = savedText
}

5. Handling User Interactions

User interactions occur through events like button clicks and touches. Android provides various ways to handle these interactions.

5.1 Using OnClickListener

You can use setOnClickListener() to handle button click events.

button.setOnClickListener {
    // Action on button click
    Toast.makeText(this, "Button has been clicked!", Toast.LENGTH_SHORT).show()
}

5.2 Handling Events in XML

You can also handle events directly in the XML layout file.

<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Click me!"
    android:onClick="onButtonClick" />

fun onButtonClick(view: View) {
    Toast.makeText(this, "XML button has been clicked!", Toast.LENGTH_SHORT).show()
}

6. Conclusion

Using views to structure screens in Android development is extremely important, and there are various methods to design layouts and interact with users. With Kotlin, these tasks can be handled easily. This course covered various topics from the fundamental concepts of views to data binding, state management, and event handling. I hope you will apply this in actual projects to develop powerful and useful Android applications.

I hope this course was helpful. If you have any questions, please leave a comment!