How to Use Radio Button in Android with Kotlin

In Android Kotlin, use RadioButton inside a RadioGroup to allow single selection. Handle user choice by setting a listener on the RadioGroup that detects which RadioButton is selected.

Syntax

A RadioButton is a selectable button that allows the user to choose one option from a set. It must be placed inside a RadioGroup to ensure only one button is selected at a time.

The RadioGroup manages the selection and provides a listener to detect changes.

xml

<RadioGroup
    android:id="@+id/radioGroup"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <RadioButton
        android:id="@+id/radioButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Option 1" />

    <RadioButton
        android:id="@+id/radioButton2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Option 2" />

</RadioGroup>

Output

UI with two radio buttons labeled 'Option 1' and 'Option 2' where only one can be selected at a time.

Example

This example shows how to set up a RadioGroup with two RadioButtons in XML and handle the selection in Kotlin code to display the chosen option.

kotlin

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

        val radioGroup = findViewById<RadioGroup>(R.id.radioGroup)

        radioGroup.setOnCheckedChangeListener { group, checkedId ->
            if (checkedId != -1) {
                val radioButton = findViewById<RadioButton>(checkedId)
                Toast.makeText(this, "Selected: ${radioButton.text}", Toast.LENGTH_SHORT).show()
            }
        }
    }
}

Output

When user selects a radio button, a toast message shows the selected option text.

Common Pitfalls

• Not placing RadioButtons inside a RadioGroup causes multiple buttons to be selectable at once.
• Forgetting to check if checkedId is not -1 before using it can cause crashes.
• Using setOnClickListener on individual RadioButtons instead of setOnCheckedChangeListener on RadioGroup can lead to inconsistent state.

xml

/* Wrong: RadioButtons outside RadioGroup allow multiple selection */
<RadioButton android:id="@+id/radioButton1" android:text="Option 1" />
<RadioButton android:id="@+id/radioButton2" android:text="Option 2" />

/* Right: Place RadioButtons inside RadioGroup */
<RadioGroup>
  <RadioButton android:id="@+id/radioButton1" android:text="Option 1" />
  <RadioButton android:id="@+id/radioButton2" android:text="Option 2" />
</RadioGroup>

Quick Reference

Tips for using RadioButton in Android Kotlin:

• Always group RadioButtons inside a RadioGroup.
• Use setOnCheckedChangeListener on RadioGroup to detect selection changes.
• Access selected button with findViewById<RadioButton>(checkedId).
• Check if checkedId is not -1 before using it.

Key Takeaways

Place RadioButtons inside a RadioGroup to allow single selection.

Use RadioGroup's setOnCheckedChangeListener to detect which RadioButton is selected.

Always check that the selected RadioButton ID is valid before accessing it.

Avoid setting click listeners on individual RadioButtons for selection handling.

Use Toast or other UI feedback to confirm user selection.