Underlining Text in Android Applications

Android provides several ways to underline text within your user interface. This tutorial will cover the most common techniques, allowing you to highlight important text and improve the user experience.

Using String Resources with HTML-like Tags

One approach is to leverage Android’s string resources and utilize basic HTML-like tags. While not a full HTML parser, Android’s string resources can interpret tags like <u> for underline, <b> for bold, and <i> for italics.

1. Define the String in res/values/strings.xml: Open your strings.xml file and define a string resource containing the text you want to underline, enclosed within <u> tags. Crucially, you need to escape the opening < character of the <u> tag as <.

   <resources>
       <string name="underlined_text">This is an &amp;lt;u&amp;gt;underlined&amp;lt;/u&amp;gt; text.</string>
   </resources>
   

2. Apply the String to Your TextView: In your layout XML or within your Activity code, reference the string resource within a TextView. When the TextView renders, it will interpret the <u> tags and underline the enclosed text.

   • In Layout XML:

     <TextView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="@string/underlined_text" />
     

   • In Activity (Java/Kotlin):

     TextView textView = findViewById(R.id.myTextView);
     textView.setText(Html.fromHtml(getString(R.string.underlined_text)));
     

     or in Kotlin:

     val textView = findViewById<TextView>(R.id.myTextView)
     textView.text = Html.fromHtml(getString(R.string.underlined_text))
     

Using PaintFlags for Dynamic Underlining

For more dynamic control, particularly when you need to underline text based on runtime conditions, you can use the PaintFlags attribute of a TextView or Button.

1. Retrieve the View: Obtain a reference to the TextView or Button in your Activity or Fragment.

2. Set the PaintFlags: Use the setPaintFlags() method to add the Paint.UNDERLINE_TEXT_FLAG to the existing paint flags.

   TextView textView = findViewById(R.id.myTextView);
   textView.setPaintFlags(textView.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);
   
   Button button = findViewById(R.id.myButton);
   button.setPaintFlags(button.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);
   

   or in Kotlin:

   val textView = findViewById<TextView>(R.id.myTextView)
   textView.setPaintFlags(textView.paintFlags or Paint.UNDERLINE_TEXT_FLAG)
   
   val button = findViewById<Button>(R.id.myButton)
   button.setPaintFlags(button.paintFlags or Paint.UNDERLINE_TEXT_FLAG)
   

This approach is particularly useful when you want to underline text based on a condition (e.g., if a certain parameter is true). You can easily toggle the underline by clearing the flag if needed.

Choosing the Right Method

• String Resources: Best suited for static text where the underline is always present. Offers a clean separation of presentation from code. Remember the HTML escaping requirements!
• PaintFlags: Ideal for dynamic scenarios where the underline needs to be toggled or changed based on runtime conditions. Provides more granular control over the visual appearance.

By understanding these techniques, you can effectively underline text in your Android applications, enhancing readability and providing a better user experience.