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Can't resolve findPreference() from MainActivity?

I'm getting a compiler error cannot resolve method findPreference when I try to intialize an OnSharedPreferencesChanged listener in my MainActivity. According to the answer here:
findPreference() should be called from a class implementing PreferenceActivity interface
but I don't understand what the code to do this would be. How can I get rid of the compiler error and successfully set listeners for preference changes?
MainActivity.java
public class MainActivity extends FragmentActivity implements SharedPreferences.OnSharedPreferenceChangeListener {
private SharedPreferences.OnSharedPreferenceChangeListener listener;
#Override
protected void onCreate(Bundle savedInstanceState) {
...
//Test preference menu
listener = new SharedPreferences.OnSharedPreferenceChangeListener() {
public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {
if (key.equals("pref_wood")) {
Preference woodPref = findPreference(key); //COMPILER ERROR HERE
MainActivity.getGLSurfaceView().setTexture("");
// Set summary to be the user-description for the selected value
woodPref.setSummary(sharedPreferences.getString(key, ""));
}
}
}
}
}

findPreference is a method which is part of both PreferenceFragment and PreferenceActivity - these are the Fragments/Activities that actually show your Preference screen (the activity is deprecated and you should be using the PreferenceFragment).
You're trying to use it in your MainActivity. This doesn't work because the Preference objects don't actually exist on this screen (they exist in another activity that usually have a PreferenceFragment as part of it). If you need to get access to a preference value of a preference in an activity that is not your preference screen, use SharedPreferences, something like:
SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
int defaultValue = getResources().getBoolean(R.bool.saved_high_score_default);
boolean wood = sharedPref.getBoolean(pref_wood, defaultValue);
You can check out the documentation for further examples.
If your MainActivity is supposed to be a screen that shows settings, then you should probably rename it and include a preference fragment inside of it.
I believe you're also going to run into trouble with setSummary because the Preference is not part of this activity, it's part of the activity where you actually modify the preferences. setSummary is used to update the actual UI of the Preference so that if you, for example, select one of three values when using a list preference, it shows the value you just selected on the screen.

getPreferences always returns default value

I have set up a PreferenceFragment with two boolean preferences. The Fragment works fine and the settings are stored when the app is closed and reopened. I am, however, having issues while trying to read these values; only the default value is returned. If I debug into the getBoolean method of SharedPreferences I see that the local HashMap is of size 0, hence the default value is returned, like this:
public boolean getBoolean(String key, boolean defValue) {
synchronized (this) {
awaitLoadedLocked();
Boolean v = (Boolean)mMap.get(key); // <-- mMap is of size 0: return defValue
return v != null ? v : defValue;
}
}
I find this strange since the preference values are obviously stored and loaded properly into the PreferenceFragment. What am I missing?
In Activity.onCreate():
PreferenceManager.setDefaultValues(this, R.xml.preferences, false);
res/xml/preferences.xml:
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
xmlns:android="http://schemas.android.com/apk/res/android">
<PreferenceCategory
android:key="mm_preferences_category_recipe_preferences"
android:title="#string/mm_preferences_category_recipe_preferences_title" >
<CheckBoxPreference
android:key="#string/mm_preferences_numbers_as_fractions_key"
android:title="#string/mm_preferences_numbers_as_fractions_title"
android:summary="#string/mm_preferences_numbers_as_fractions_summary"
android:defaultValue="true" />
<CheckBoxPreference
android:key="#string/mm_preferences_comma_as_decimal_separator_key"
android:title="#string/mm_preferences_comma_as_decimal_separator_title"
android:summary="#string/mm_preferences_comma_as_decimal_separator_summary"
android:defaultValue="true" />
</PreferenceCategory>
</PreferenceScreen>
My PreferenceFragment class:
public class MiasMatPreferencesFragment extends PreferenceFragment
{
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
}
}
Now, doing this anywhere in the app, returns only the default values (true in both cases), even though the PreferenceFragment shows that the values are set to false (if so):
boolean foo = getPreferences(Context.MODE_PRIVATE).getBoolean(getString(R.string.mm_preferences_numbers_as_fractions_key), true);
boolean bar = getPreferences(Context.MODE_PRIVATE).getBoolean(getString(R.string.mm_preferences_comma_as_decimal_separator_key), true);

After fiddling around with this for some hours I figured out the reason why this didn't work for me. There are several SharedPreferences inside a single app, which I didn't realize. This means that (1) Activity.getPreferences(int mode), (2) Context.getSharedPreferences(String name, int mode) and (3) PreferenceManager.getDefaultSharedPreferences(Context context) returns different instances of SharedPreferences.
In my case, the solution was to use PreferenceManager.getDefaultSharedPreferences(Context context). This is because I use a custom library for backwards compatibility of PreferenceFragment. This library writes to the default preferences file.
From the docs:
PreferenceManager.getDefaultSharedPreferences(Context context)
Gets a SharedPreferences instance that points to the default file that is used by the preference framework in the given context.
So this is preferences for the given Context or Activity at any time using the default filename for preferences. This is a static instance of the PreferenceManager class.
Context.getSharedPreferences(String name, int mode)
Retrieve and hold the contents of the preferences file 'name', returning a SharedPreferences through which you can retrieve and modify its values. Only one instance of the SharedPreferences object is returned to any callers for the same name, meaning they will see each other's edits as soon as they are made.
Using this method you can distinguish between several preference files, using the String argument.
Activity.getPreferences(int mode)
Retrieve a SharedPreferences object for accessing preferences that are private to this activity.
This method calls directly to the previous one like this: getSharedPreferences(getLocalClassName(), mode). Hence it points to a file depending on the name of the Activity.
Other related questions (possible duplicates):
Difference between getDefaultSharedPreferences and getSharedPreferences
PreferenceManager.getDefaultSharedPreferences() vs getPreferences()

How to replace one string with another in whole application in android?

I have to change one text with another when user select option from settings,For example
I have to change Kilometers in to miles when user select it from option. And When i select it
i have to change kilometer into Miles thought the application , Please help me if anyone knows
how to do it?

Declare these globally for convenience:
SharedPreferences sharedPrefs;
Editor editor;
private static final String PRIVATE_PREF = "current_selection";
And then in the onCreate() or it's equivalent:
sharedPrefs = getApplicationContext().getSharedPreferences(PRIVATE_PREF, Context.MODE_PRIVATE);
// SET THE DEFAULT VALUE
editor = sharedPrefs.edit();
editor.putString("value", "kilometers");
// DONT SKIP THIS STEP
editor.commit();
Finally, wherever you need to check which of the two is the current selected value (Kilometers / Miles):
String strSetting = sharedPrefs.getString("value", null);
Now, you can use the String strSetting to check the value of the setting, and run the appropriate code. I am assuming it has something to do with conversion perhaps.
NOTE: If you are using the above (retrieving) in another Activity, you will need to instantiate this again:
SharedPreferences sharedPrefs = getApplicationContext().getSharedPreferences(PRIVATE_PREF, Context.MODE_PRIVATE);
String strSetting = sharedPrefs.getString("value", null);
Anytime you want to change the setting, just use the first piece of code. For example, if you change from Kilometers to Miles:
// SET THE A NEW VALUE
editor = sharedPrefs.edit();
editor.putString("value", "miles");
// DONT SKIP THIS STEP
editor.commit();
You can read more about SharedPreferences here

Declare a static String in your MainActivity (or elsewhere).
class MainActivity {
public static String distance = "kilometer";
}
You can change the String from anywhere with
MainActivity.distance = "miles";
Then you can use the distance String allover your app.

Preference not getting initialised with default values from the xml

This question has been asked many times in this forum. But I feel it still need to be cleared for me .
public class PrefTest extends Activity {
public Button bt_start= null;
SharedPreferences mSharedPreferences;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.main);
bt_start = (Button) findViewById(R.id.button1);
bt_start.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Log.d("TEST","");
PreferenceManager.setDefaultValues(getApplicationContext(),
R.xml.settings_org, true);
mSharedPreferences = PreferenceManager
.getDefaultSharedPreferences(getApplicationContext());
Boolean test = false;
test = mSharedPreferences.getBoolean("auto_launch_key", true);
Log.d("TEST","test = "+test);
}
});
super.onCreate(savedInstanceState);
}
#Override
protected void onStart() {
super.onStart();
}
}
In the above code
Log.d("TEST","test = "+test);
always prints true , though I have set default value in xml as false(as below)
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >
<PreferenceCategory android:title="settings" >
<CheckBoxPreference android:key="auto_launcvh_key"
android:summaryOn="..."
android:summaryOff="---"
android:title="auto_launch_string" android:defaultValue="false" />
</PreferenceCategory>
</PreferenceScreen>
Am expecting the setDefaultValues to take the defaults values form the XML and initialize the preference.
Am I wrong in my understanding?

UPDATE
On closer inspection I can see you probably aren't correctly retrieving the SharedPreference object. although I have not tried it, to make this test work I assume you would have to call getSharedPreferences (String name, int mode) with the name of your XML file to get the object which stores the values defined in your XML file.
getDefaultSharedPreferences (Context context) states:
Gets a SharedPreferences instance that points to the default file that
is used by the preference framework in the given context. Parameters
context The context of the preferences whose values are wanted.
Returns
A SharedPreferences instance that can be used to retrieve and listen
to values of the preferences.
Your file doesn't seem to be the default file and thus the preferences you are trying to call don't exist.
Generally the way to deal with preferences is to sub class a PreferenceActivity which will create a preferences interface but I appreciate you are just trying to write a simple test.
Also I assume the CheckBoxPreference android:key="auto_launcvh_key"is a typo when writing the question. I think I checked the key when first writing this answer and it was CheckBoxPreference android:key="auto_launch_key"
ORIGINAL
Firstly I would change test = mSharedPreferences.getBoolean("auto_launch_key", true); to test = mSharedPreferences.getBoolean("auto_launch_key", false); if it now returns false then the preference doesn't exist in the system so there is a problem with your environment. Try cleaning the project and re-installing.
Secondly in the docs it states
readAgain - Whether to re-read the default values. Note: this will NOT
reset preferences back to their default values. For that
functionality, use getDefaultSharedPreferences(Context) and clear it
followed by a call to this method with this parameter set to true.
Therefore if the preference already exists in the system as true this will not overwrite and so a re-installation should sort this out as well. or you could try calling clear() on mSharedPreferences and then calling PreferenceManager.setDefaultValues(getApplicationContext(), R.xml.settings_org, true);
If this doesn't work can you post complete XML.

The answer is actually very simple.
Boolean values in a preference file are only present when they are true so when reading the boolean value you need to set default value to false:
test = mSharedPreferences.getBoolean("auto_launch_key", false);
So when the preferences in xml is true it reads true and otherwise uses the default of getBoolean. I noticed while debugging there aren't any Boolean preferences with false as the value.

How to update internal values of a PreferenceActivity when SharedPreferences change

I use a Preference in a PreferenceActivity to load default values: when this specific Preference is clicked, something like this happens:
private String mResetKeys = "key1,key2,key3";
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getContext());
SharedPreferences.Editor prefs_editor = prefs.edit();
for (String current_pref : mResetKeys.split(",")) {
prefs_editor.remove(current_pref);
}
prefs_editor.commit();
But afterwards, the Preferences whose corresponding SharedPreference was reset still show the old value - it seems to be cached in the Preference. Only when I leave the PreferenceActivity and reopen it, the Preferences show the new values.
How can I update the PreferenceActivity programmatically?

I had a similar problem. This probably isn't the most correct fix but it worked for my purposes. Right after I did the commits, I called the Activity.recreate(); method.
The activity will restart (onDestroy()/onCreate()/etc) but for my purposes all I needed was a special handling on one preference. I listened for a certain preference with an OnPreferenceClickListener and made an alert dialog box with a kind of warning message and an option to change their mind. If they did want to change their mind, I did my commit of the new value to the preference activity and then called recreate() so that the checkbox preference would be updated.
However, I am also interested in a way to do this without recreating the activity...

Update preference value without reloading PreferenceActivity
from http://liquidlabs.ca/2011/08/25/update-preference-value-without-reloading-preferenceactivity/
Here is how to update default shared preference value of target element (in this case EditTextPreference)
public class YourCustomPreference extends PreferenceActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Load the preferences from an XML resource
addPreferencesFromResource(R.xml.preferences);
}
// some logic goes above, when you want to reset value and update EditTextPreference value
// For convenience, I am going to wrap two different task in different methods
private void resetPreferenceValue() {
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
SharedPreferences.Editor prefEditor = sharedPref.edit(); // Get preference in editor mode
prefEditor.putString("your_edit_text_pref_key", "DEFAULT-VALUE"); // set your default value here (could be empty as well)
prefEditor.commit(); // finally save changes
// Now we have updated shared preference value, but in activity it still hold the old value
this.resetElementValue();
}
private void resetElementValue() {
// First get reference to edit-text view elements
EditTextPreference myPrefText = (EditTextPreference) super.findPreference("your_edit_text_pref_key");
// Now, manually update it's value to default/empty
myPrefText.setText("DEFAULT-VALUE"); // Now, if you click on the item, you'll see the value you've just set here
}
}