Setting UI preference Summary field to the value of the preference

This worked for me.

public class PrefsActivity extends PreferenceActivity implements OnSharedPreferenceChangeListener
{
    private Preference pref;
    private String summaryStr;
    String prefixStr;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
       super.onCreate(savedInstanceState);
       addPreferencesFromResource(R.xml.prefs);

       SharedPreferences sharedPref = getPreferenceScreen().getSharedPreferences();
       sharedPref.registerOnSharedPreferenceChangeListener(this);      
    }

    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key)
    {
        //Get the current summary
        pref = findPreference(key);
        summaryStr = (String)pref.getSummary();

        //Get the user input data
        prefixStr = sharedPreferences.getString(key, "");

        //Update the summary with user input data
        pref.setSummary(summaryStr.concat(": [").concat(prefixStr).concat("]"));
    }
}   

What I usually do is:
1 - Make a new class which extends the kind of preference I need to show (1 per preference type) 2 - Inside its code, do the appropriate actiob to show the updated summary
3 - Refer this class in the res/xml/preferences.xml file

Let me swo a small example, good for an EditTextPreference:

CLS_Prefs_Edit.java

/**
 * CLS_Prefs_Edit class
 *
 * This is the class that allows for a custom EditTextPrefence
 * (auto refresh summary).
 *
 * @category    Custom Preference
 * @author        Luca Crisi ([email protected])
 * @copyright    Luca Crisi
 * @version        1.0
 */
package com.your_name.your_app;

/* -------------------------------- Imports --------------------------------- */

import android.content.Context;
import android.preference.EditTextPreference;
import android.util.AttributeSet;

public final class CLS_Prefs_Edit
extends EditTextPreference
{

    /* ---------------------------- Constructors ---------------------------- */

    public CLS_Prefs_Edit(final Context ctx, final AttributeSet attrs)
    {
        super(ctx, attrs);
    }
    public CLS_Prefs_Edit(final Context ctx)
    {
        super(ctx);
    }

    /* ----------------------------- Overrides ------------------------------ */

    @Override
    public void setText(final String value)
    {
        super.setText(value);
        setSummary(getText());
    }
}

res/xml/preferences.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
    xmlns:android="http://schemas.android.com/apk/res/android"
    >
    <PreferenceCategory android:title="@string/pref_phone_cat">
<!-- NORMAL EditTextPreference, NO summary update -->
<!--         <EditTextPreference -->
<!--             android:widgetLayout="@layout/arr_dn" -->
<!--             android:key="phone" -->
<!--             android:title="@string/pref_phone_title" -->
<!--             android:summary="@string/pref_phone_summ" -->
<!--             android:defaultValue="" -->
<!--             android:inputType="phone" -->
<!--             android:digits="+1234567890" -->
<!--         /> -->
<!-- MY EditTextPreference, WITH summary update -->
        <com.your_name.your_app.CLS_Prefs_Edit
            android:widgetLayout="@layout/arr_dn"
            android:key="phone"
            android:title="@string/pref_phone_title"
            android:summary="@string/pref_phone_summ"
            android:defaultValue=""
            android:inputType="phone"
            android:digits="+1234567890"
        />
    </PreferenceCategory>
</PreferenceScreen>

Of course, set your strings in /res/values/strings, and you're done.

Note that this solution works for both PreferenceFragments and PreferenceActivities.
I'm using it for an app tha runs on 2.2 Froyo (showing a PreferenceActivity) as well as on 4.4 KitKat (showing a PreferenceFragment)

I hope it helps.

I am new too so may not be the best code but this is similar to what I am doing. You probably want to register you listener onResume and unregister it onPause though rather than onCreate. I hope this helps.

Mainly you just need to grab the pref, the pref value and set the summary.

public class MyPreferenceActivity extends PreferenceActivity implements
        OnSharedPreferenceChangeListener {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preference);
        SharedPreferences sp = getPreferenceScreen().getSharedPreferences();
        EditTextPreference editTextPref = (EditTextPreference) findPreference("thePrefKey");
        editTextPref
                .setSummary(sp.getString("thePrefKey", "Some Default Text"));
    }

    protected void onResume() {
        super.onResume();
        getPreferenceScreen().getSharedPreferences()
                .registerOnSharedPreferenceChangeListener(this);
    }

    protected void onPause() {
        super.onPause();
        getPreferenceScreen().getSharedPreferences()
                .unregisterOnSharedPreferenceChangeListener(this);
    }

    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
            String key) {
        Preference pref = findPreference(key);
        if (pref instanceof EditTextPreference) {
            EditTextPreference etp = (EditTextPreference) pref;
            pref.setSummary(etp.getText());
        }
    }
}