Develop Reference

Android Interface Implementation Error for Network Fragment

I wanted to make a network fragment on my Android app so I could upload and download information from my database server. Following the guide on Android networking on the Developer page and the corresponding example project on Github, I created a demo to test a network connection.
I copied the files DowloadCallback.java (contains the implemented network interface) and NetworkFragment.java (the network fragment thread) word for word from the example project and added the necessary permissions in AndroidManifest.xml.
When I tried to implement the fragment into my activity, I got errors in several rather odd and counterintuitive places:
Code
public class MainActivity extends FragmentActivity implements DownloadCallback {
...
#Override
public void updateFromDownload(String result) {
...
}
}
Errors
Class 'MainActivity' must either be declared in abstract or implement method 'updateFromDownload(T)' in 'DownloadCallback'
Method does not override method from its superclass
The public class says it needs a particular method for the class to implement DownloadCallback, but when I add such method it says that it does not exist in its superclass. How can these errors coexist? How can I fix this?
By the way, this is the exact same way the main activity class is defined in the sample project. Also I have posted this as an issue on Github but I am hoping to get a quicker response and attention here.

base on this You have to define <T> for DownloadCallback
In your case T is String
So change your code like below
public class MainActivity extends FragmentActivity implements DownloadCallback<String>

android how and when to use getSupportFragmentManager (newbie is confused)

I'm just getting started with Android development and am trying to follow an example in a book and it's not compiling.
The book has me creating a Fragment in my application and then interacting with that fragment in my MainActivity; specifically the book says to call getFragmentManager().findFragmentByID(..) in the main activity, in order to access this fragment, but this is returning an error that the results of getFragmentManager can't be converted to the right type.
So I started poking around and noticed that by default, my installation of Android Studio is apparently using the v4 support library and so my Fragments are v4 Fragments and not the standard sdk Fragments (please correct me if I'm misinterpreting the situation).. and because of this, the call to getFragmentManager is apparently not the right way to get at a v4 Fragment.
Apparently I'm supposed to be calling getSupportFragmentManger instead, but Android Studio says that's not defined. I tried guessing what kind of import I might need in my main activity for it to be able to see getSupportFragmentManager, but I can't seem to figure that out either.
Any help at straightening this out would be very much appreciated.
I have looked at the v4 docs on google's site but honestly to a newbie it's not clear what calls go with what.
Michael

If you want to use support classes in your Activity, then it should also be an Activity from support library.
To accomplish that your Activity must extend AppCompatActivity.
public class MainActivity extends AppCompatActivity {
//Your code that calls getSupportFragmentManager()
}

You should choose some options here:
use android.support.v7.app.AppCompatActivity or android.support.v4.app.FragmentActivity as a parent of your activity
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentManager supportFragmentManager = getSupportFragmentManager();
}
}
Instead of android.support.v4.Fragment, use android.app.Fragment and simply use android.app.FragmentManger
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
android.app.FragmentManager fragmentManager = getFragmentManager();
}
}

Android create a PreferenceFragment without a PreferenceActivity

I added a side menu to my Application and I managed to change the content with fragments. Now I am trying to do the Preferences, but I don't want to use a PreferenceActivity because I want to do my application with fragments because I don't want to do the NavigationDrawer twice (For my main activity displaying the fragments and for the PreferenceActivity).
I found the class PreferenceFragment but after alot of research I found out that appearantly it just is a part of the SettingsActivity and when I try to addPreferenceFromResouce in the PreferenceFragment and then launch the fragment, it crashes.
So basically I am trying to find a way to display a SettingsFragment without any extra activity just by calling fragmentManager.beginTransaction().replace(R.id.contentFrame, settingsFragment).commit() just as I do with my different fragments.
I hope I asked my question understandable (I am sorry if I didn't). Thanks for your time and your help.

I found the solution myself now. It wasn't very hard.
I simply created a normal PreferenceFragment and you can use it like any other fragment without a PreferenceActivity.
public class PreferenceFragment extends android.preference.PreferenceFragment {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
}}
I then replaced it using
getFragmentManager().beginTransaction().replace(R.id.contentFrame, preferenceFragment).commit();
as you normally would.
This worked great for me. I hope it also does for you.

calling static methods from other classes

so i'm having some problems integrating scoreloop into my game. I use cocos2dx which is written in c++ and uses the ndk. The main application class is derived from activity and not from android.app.application. Adding a button to the layout and using it to bring up a scoreboard or submit a score works,but it doesn't connect to the internet. i've found a solution to this here : scoreloop support forum or more specifically
Yes, using libgdx seems to be the issue. libgdx brings it's own Application class that is actually derived from Android's Activity, not Application. The helloworld sample from libgdx does not come with an (Android) Application class at all, here is how to add one:
Create a new class that extends android.app.Application (not com.badlogic.gdx.backends.android.AndroidApplication)
In the AndroidManifest.xml find the tag and the name of the created class as an attribute: android:name="YourApplication"
Add the method public void onCreate() to that class and initialize Scoreloop there.
so following that i created this :
public class scoreLooped extends android.app.Application{
public void onCreate(Bundle savedInstanceState){
ScoreloopManagerSingleton.init(this, "redacted");
}
public void onTerminate()
{
ScoreloopManagerSingleton.destroy();
}
}
and i create this class from my main activity class like this :
public class wordsweeper extends Cocos2dxActivity implements OnScoreSubmitObserver{
private Cocos2dxGLSurfaceView mGLView;
private static scoreLooped a;
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
wordsweeper.a = new scoreLooped();
//Set the observer equal to an instance of this class
ScoreloopManagerSingleton.get().setOnScoreSubmitObserver(this);
and the last line is where it crashes with an error "Caused by: java.lang.IllegalStateException: ScoreloopManagerSingleton.init() must be called first" so obviously my scoreLooped class doesn't call the scoreloopmanager. I've thought about using the scorelooped class to submit,retrieve scoreboards but it seems that i can't do that without extending activity. I'm pretty new to java so i might be missing something obvious so it would be great if somebody could point me in the right direction.

It seems that you need to create your own Application class and call ScoreloopManagerSingleton.init() there. See the answer here, which references some example documentation: http://support.scoreloop.com/discussions/problems/789-illegalstateexception-scoreloopmanagersingletoninit-can-be-called-only-once

ActionBar in PreferenceActivity

In my application I am using the new Action Bar Compatibility sample from Google (located at <sdk>/samples/android-<version>/ActionBarCompat) which works great. The only problem I have is applying this to my PreferenceActivity in order to get a screen like the settings in the Android Market (see picture).
To fill the ActionBar with icons, each Activity must extend the ActionBarActivity class. The problem is that my Activity already extends PreferenceActivity and in Java classes can not extend more than one class.
There must be a way to get the ActionBar together with a PreferenceScreen. I would be glad if anybody could provide a solution for this common issue.
P.S.: A solution like in How to add a button to PreferenceScreen does not fit because the ActionBar is actually the title bar and so this is more a Java than a layout thing.

Edit: My answer below is rather hacky and it seems like it is now outdated (for pre Android 3.0) Have a look at the other answers for less hacky and more current solutions ~pyko 2014-09-01
I managed to get it working - not sure if this is the nicest/cleanest solution, but it works.
Had to make the following changes:
Make a copy of ActionBarActivity and have the new class extend PreferenceActivity
public abstract class ActionBarPreferenceActivity extends PreferenceActivity {
// contents exactly the same as 'ActionBarActivity'
}
Modify onCreate() in ActionBarHelperBase.java slightly - make a special case for PreferenceActivity classes
#Override
public void onCreate(Bundle savedInstanceState) {
// If the activity is a PreferenceActivity, don't make the request
if (!(mActivity instanceof PreferenceActivity)) {
mActivity.requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
}
Have your PreferenceActivity extend this class and add request for FEATURE_CUSTOM_TITLE before you call super.onCreate()
public class MyPreferenceActivity extends ActionBarPreferenceActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
requestWindowFeature(Window.FEATURE_CUSTOM_TITLE); // add this line
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
// etc etc
}
// etc etc
}
As far as I can tell, changes 2 and 3 are needed because for PreferenceActivity:
"As soon as you call super.onCreate(), the ViewGroup will be set up and so, you are not allowed to change the Window's parameters." (see Oliver's comment to the answer)
I guess the order of how components in PreferenceActivity activities are created is different to plain Activity activities .

If you want to try a PreferenceFragment implementation based on support-v4 Fragment:
https://github.com/kolavar/android-support-v4-preferencefragment
I´m using it by myself and it isnt much work turning PreferenceActivity into PreferenceFragment.

Can you just clone the code for ActionBarActivity, and change "extends Activity" to "extends PreferenceActivity"? Then extend your new class instead of ActionBarActivity.
From all the Google apps I've seen, though, it seems unusual to put buttons in the action bar of a PreferenceActivity. If you're not putting buttons on it, you could just use a values-v11 alternate style resource to show the holo theme, and set that style in the manifest for your PreferenceActivity.

I used in my application this actionbar
https://github.com/johannilsson/android-actionbar and it's work great with this thread How to add a button to PreferenceScreen

I'd like to thank to #pyko providing a great answer, but it has problem that it won't work well on HoneyComb and above. well you can have a hack way to get it around like #AndroidDev said;
But #pyko is gonna pollute the ActionBarHelperBase class, and #AndroidDev isn't very transparent.The best way is to create ActionBarActivityPreferences who extends from PreferenceActivity; and in onCreate method, change the order of calling parent method:
#Override
protected void onCreate(Bundle savedInstanceState) {
//IMPORTATNT: MAKE SURE actionBarHelper called before super;
//as super oncreate of prefenceactivity is actuallying setting the content view
mActionBarHelper.onCreate(savedInstanceState);
super.onCreate(savedInstanceState);
}
why calls 'mActionBarHelper.onCreate(savedInstanceState);' before 'super.onCreate(savedInstanceState);' , that is because super (i.e. PreferenceActivity) is actually setting the content view in its onCreate method, which would cause crash ("requestFeature() must be called before adding content'). SO what you need do is to swap the order, make sure ' mActionBarHelper.onCreate(savedInstanceState);' is called before super.
In this way, we don't need to pollute the 'ActionBarHelperBase' yet we keep SettingActivity very clean because we encapsulate the tricky detail to 'ActionBarActivityPreferences' and bang!

You can easily add action bar in preference activity by the following changes:
In AndroidManifest.xml :
<activity
android:name=".activity.SettingsActivity"
android:theme="#style/SettingsTheme"
android:label="Settings"/>
In v21/styles.xml
<style name="SettingsTheme" parent="#android:style/Theme.Material.Light.DarkActionBar">
<item name="android:colorPrimary">#color/colorPrimary</item>
<item name="android:colorPrimaryDark">#color/colorPrimaryDark</item>
</style>
In v14/styles.xml for Back API support:
<style name="SettingsTheme" parent="#android:style/Theme.Holo.Light.DarkActionBar">
<item name="android:actionBarStyle">#style/ActionBar.V14.Movie.NoTitle</item>
</style>

Thanks, just an update, you need to add an if statement before the Custom Title line to support HoneyComb and above.
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB)
requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);

You can get a ActionBarSherlock lib and let you code extends SherlockPreference;