Android Preferences NullException

Someone can help me?

i'm begginer in Android and i don't know where is my wrong.

Thanks in advance!

Error Log

01-22 11:45:32.722 13037-13037/com.example.android.sunshine.app E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.sunshine.app, PID: 13037
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.sunshine.app/com.example.android.sunshine.app.SettingsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.preference.Preference.setOnPreferenceChangeListener(android.preference.Preference$OnPreferenceChangeListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2491)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2564)
at android.app.ActivityThread.access$800(ActivityThread.java:170)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1441)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5576)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:956)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:751)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.preference.Preference.setOnPreferenceChangeListener(android.preference.Preference$OnPreferenceChangeListener)' on a null object reference
at com.example.android.sunshine.app.SettingsActivity.bindPreferenceSummaryToValue(SettingsActivity.java:40)
at com.example.android.sunshine.app.SettingsActivity.onCreate(SettingsActivity.java:30)
at android.app.Activity.performCreate(Activity.java:6041)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1111)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2437)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2564) 
at android.app.ActivityThread.access$800(ActivityThread.java:170) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1441) 
at android.os.Handler.dispatchMessage(Handler.java:111) 
at android.os.Looper.loop(Looper.java:194) 
at android.app.ActivityThread.main(ActivityThread.java:5576) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:956) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:751)

strings.xml

<string name="app_name">Sunshine</string>
<string name="hello_world">Hello world!</string>
<string name="action_settings">Settings</string>
<string name="action_refresh" translatable="false">Refresh</string>
<string name="title_activity_detail">Details</string>
<string name="title_activity_settings">Settings</string>


<string name="pref_location_label" >Location</string>

<string name="pref_location_key" translatable="false">location</string>

<string name="pref_location_default" translatable="false">94043</string>

SettingsActivity.java

import android.os.Bundle;
import android.preference.ListPreference;
import android.preference.Preference;
import android.preference.PreferenceActivity;
import android.preference.PreferenceManager;

public class SettingsActivity extends PreferenceActivity
        implements Preference.OnPreferenceChangeListener {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        addPreferencesFromResource(R.xml.pref_general);

        bindPreferenceSummaryToValue(findPreference(getString(R.string.pref_location_key)));
    }

    private void bindPreferenceSummaryToValue(Preference preference) {

        preference.setOnPreferenceChangeListener(this);

        onPreferenceChange(preference,
                PreferenceManager
                        .getDefaultSharedPreferences(preference.getContext())
                        .getString(preference.getKey(), ""));
    }

    @Override
    public boolean onPreferenceChange(Preference preference, Object value) {
        String stringValue = value.toString();

        if (preference instanceof ListPreference) {
            // For list preferences, look up the correct display value in
            // the preference's 'entries' list (since they have separate labels/values).
            ListPreference listPreference = (ListPreference) preference;
            int prefIndex = listPreference.findIndexOfValue(stringValue);
            if (prefIndex >= 0) {
                preference.setSummary(listPreference.getEntries()[prefIndex]);
            }
        } else {
            // For other preferences, set the summary to the value's simple string representation.
            preference.setSummary(stringValue);
        }
        return true;
    }

}

that's my pref_general.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
    >

    <EditTextPreference
        android:key="pref_location_key"
        android:title="@string/pref_location_label"
        android:defaultValue="@string/pref_location_default"
        android:inputType="text"
        android:singleLine="true" />
</PreferenceScreen>

I tried some ways to fix this problem, but without sucess. This error happens when a push the button "Settings", then my app close and show me a error message.

Solution

Look at the image above to see that the preference object inside the bindPreferenceSummaryToValue is null. This line, to be more precise

preference.setOnPreferenceChangeListener

How to debug

Make sure the findPreference actually returns you something and not a null value. Use a log statement in there to see that.
If the first step gives you a NULL value, check if the pref_location_key actually exists or not and then pass it to the bind method.
Read the javadoc for this function.

findPreference - Javadoc