How to Underline Text of Button in Android?

Code only

Java:

Button button = (Button) findViewById(R.id.park);
button.setPaintFlags(button.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);

Kotlin:

val button = findViewById<Button>(R.id.park);
button.paintFlags = button.paintFlags or Paint.UNDERLINE_TEXT_FLAG

Resource string with static text (xml only)

If you have a static text in your resources you could also use the following approach in your strings.xml:

<string name="underlined_text"><u>I\'m underlined</u></string>

Resource string with dynamic text (xml + code)

If you're using dynamic text but don't like the first approach (which isn't the best imho either), you could also use following:

strings.xml

<string name="underlined_dynamic_text"><u>%s</u></string>

Java:

button.setText(getString(R.string.underlined_dynamic_text, "I'm underlined");

Kotlin:

button.text = getString(R.string.underlined_dynamic_text, "I'm underlined")

This should make your ButtonText bold, underlined and italic at the same time.

strings.xml

<resources>
    <string name="register"><u><b><i>Copyright</i></b></u></string>
</resources>

To set this String to your TextView, do this in your main.xml

<?xml version="1.0" encoding="utf-8"?>
<Button xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/btn1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:text="@string/register" />

You can't set underline from xml file. To set underline using code you need to set the underline flag on button.

Button button = (Button) findViewById(R.id.park);
button.setPaintFlags(button.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);