How to define bold in an Android selector?

The style has no selector: using one will either break the build/runtime or will have no effect and be neglected. There are only two types of selectors: for colors and for drawables.

So, there is only one option: apply bold style on the fly, possibly, by listening to check state changes.

=== Example ===

MainActivity.java:

package com.example.radiobuttontest;import android.os.Bundle;import android.app.Activity;import android.graphics.Typeface;import android.widget.CompoundButton;import android.widget.RadioButton;import android.widget.RadioGroup;public class MainActivity extends Activity implements CompoundButton.OnCheckedChangeListener {    private RadioGroup mGroup2;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mGroup2 = (RadioGroup)findViewById(R.id.radioGroup2);        RadioButton button1 = (RadioButton)findViewById(R.id.option_1);        button1.setOnCheckedChangeListener(this);    }    @Override    protected void onResume() {        super.onResume();        RadioButton checked = (RadioButton)findViewById(mGroup2.getCheckedRadioButtonId());        checked.setTypeface(Typeface.DEFAULT_BOLD);    }    @Override    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {        buttonView.setTypeface(isChecked ? Typeface.DEFAULT_BOLD : Typeface.DEFAULT);    }}

layout/activity_main.xml:

<?xml version="1.0" encoding="utf-8"?><RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/radioGroup2"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="horizontal" >    <RadioButton        android:id="@+id/option_1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:checked="true"        android:text="@string/option_1"        android:textColor="@drawable/radio_picker_color" />    <RadioButton        android:id="@+id/option_2"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="@string/option_2"        android:textColor="@drawable/radio_picker_color" /></RadioGroup>

drawable/radio_picker_color.xml [I changed colors you have used (they are very faint) in the question with "#0099CC" for demonstration purposes]:

<?xml version="1.0" encoding="utf-8"?><selector xmlns:android="http://schemas.android.com/apk/res/android">     <!-- checked -->     <item android:state_checked="true"         android:color="#0099CC" />     <!-- default -->     <item android:color="#0099CC" /></selector>

Result:

Hope this helps.

You can do something like this

Create your own style e.g. mystyle.xml

<style name="mystyle">      <item name="android:textColor">#ffffff</item>    <item name="android:textStyle">bold</item></style>

Now call this in your selector like this

<selector xmlns:android="http://schemas.android.com/apk/res/android"><item       android:state_checked="true"      style="@style/mystyle" /></selector>

Use

android:textStyle = "bold"