Develop Reference

why am I getting an Theme related error in android studio?

I am following a tutorial on how to make a launcher but for some reason when I add this line of code to my main activity with in the manifest the app crashes saying that my app has stopped
android:theme="#android:style/Theme.Holo.Wallpaper.NoTitleBar"
10-18 15:04:25.245 18122-18122/com.example.harrops.h20droidlauncher E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.harrops.h20droidlauncher, PID: 18122
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.harrops.h20droidlauncher/com.example.harrops.h20droidlauncher.HomeLayout}: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2400)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2458)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1305)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5598)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.support.v7.app.AppCompatDelegateImplV7.createSubDecor(AppCompatDelegateImplV7.java:309)
at android.support.v7.app.AppCompatDelegateImplV7.ensureSubDecor(AppCompatDelegateImplV7.java:278)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:252)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
at com.example.harrops.h20droidlauncher.HomeLayout.onCreate(HomeLayout.java:13)
at android.app.Activity.performCreate(Activity.java:5459)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2458)
            at android.app.ActivityThread.access$900(ActivityThread.java:172)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1305)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:146)
            at android.app.ActivityThread.main(ActivityThread.java:5598)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
            at dalvik.system.NativeStart.main(Native Method)
if I remove the line of code the app runs just fine.
Any help would be great. Thanks as always in advance.

To change the Background use:
android:background=" "
You selected a wallpaper.
Try this instead
android:background="#b6db49">
Below you have said that you want to use the theme. So you have to go in the manifest and edit the theme there which is
<activity
android:name=".MainActivity"
android:label="#string/app_name"
android:theme="#android:style/Theme.Holo.Wallpaper.NoTitleBar">

If You've begun Your project in Android Studio by default main activity extends
ActionBarActivity which requires the AppCompat theme. Change the Java inheritance from ActionBarActivity to Activity and leave the theme in the manifest as it is. Or use AppCompat theme.

NPE Error inflating class fragment: NavigationDrawerFragment

When I create a new navigation drawer activity in Android Studio, the basic example runs perfectly. I've changed a few lines to integrate Material Design and v4 - v7 support, and consequently the app breaks. I also included in some lines of basic code from Firebase that does a simple auth with Google+.
Starting the app returns a runtime exception, and "error inflating class fragment" message.
I'm guessing that the NPE is coming from the view not being inflated, but I have no idea how that is happening.
Below is my logcat, my activities, and my layouts. Any help or guidance would be appreciated.
Logcat:
11-24 16:29:26.735 6127-6127/com.starkenglish E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.starkenglish, PID: 6127
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.starkenglish/com.starkenglish.MainActivity}: android.view.InflateException: Binary XML file line #19: Error inflating class fragment
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2212)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:796)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:612)
at dalvik.system.NativeStart.main(Native Method)
Caused by: android.view.InflateException: Binary XML file line #19: Error inflating class fragment
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:713)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:343)
at android.app.Activity.setContentView(Activity.java:1929)
at com.starkenglish.MainActivity.onCreate(MainActivity.java:110)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5146)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:796)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:612)
            at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.starkenglish.NavigationDrawerFragment.onCreateView(NavigationDrawerFragment.java:101)
at android.app.Fragment.performCreateView(Fragment.java:1700)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:866)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1040)
at android.app.FragmentManagerImpl.addFragment(FragmentManager.java:1142)
at android.app.Activity.onCreateView(Activity.java:4786)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:689)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
            at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:343)
            at android.app.Activity.setContentView(Activity.java:1929)
            at com.starkenglish.MainActivity.onCreate(MainActivity.java:110)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5146)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:796)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:612)
            at dalvik.system.NativeStart.main(Native Method)
To keep this post clean, I have posted my code as GIST on github.
MainActivity.java:
https://gist.github.com/markbratanov/a94291edaf02b0b236d3
NavigationDrawerFragment.java:
https://gist.github.com/markbratanov/92bb583f14604b68b34d
fragment_main.xml:
https://gist.github.com/markbratanov/d1bda8b3c99d47e0257c
fragment_navigation_drawer.xml:
https://gist.github.com/markbratanov/5f5e334e40e253736e49
If there is missing code / files please let me know and I'll include it immediately.

your main activity extends FragmentActivity, and in order to get an actionBar
which is listed in your NavigationDrawerFragment line 101, just like the error says
mDrawerListView.setAdapter(new ArrayAdapter<String>(
getActivity().getActionBar().getThemedContext(), <== this is the null part
android.R.layout.simple_list_item_activated_1,
android.R.id.text1,
new String[]{
getString(R.string.title_section1),
getString(R.string.title_section2),
getString(R.string.title_section3),
}));
you need to extend the ActionBarActivity from the app compat
quote from the documentation
ActionBarCompat contains one Activity class which all of your Activity
classes should extend: ActionBarActivity. This class itself extends
from FragmentActivity so you can continue to use Fragments in your
application.

Default Activity Not Found IntelliJ

When I run my app, I am taken to an Edit Configuration screen and it says, "Default Activity not found". I believe I got this error after I tried to import a library from another app I have.
I keep getting this error even after I rebuilt my project, restarted IntelliJ IDEA and file > Invalidated Cache. I did set a main activity so I'm not sure why it says that.
Here's the exception:
Process: com.example.Device, PID: 24635
java.lang.RuntimeException: Unable to instantiate application android.app.Application: java.lang.IllegalStateException: Unable to get package info for com.example.Device; is package not installed?
at android.app.LoadedApk.makeApplication(LoadedApk.java:507)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4301)
at android.app.ActivityThread.access$1500(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.IllegalStateException: Unable to get package info for com.example.Device; is package not installed?
at android.app.LoadedApk.initializeJavaContextClassLoader(LoadedApk.java:368)
at android.app.LoadedApk.getClassLoader(LoadedApk.java:321)
at android.app.LoadedApk.makeApplication(LoadedApk.java:500)
            at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4301)
            at android.app.ActivityThread.access$1500(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)
I can run my application anyway even though the "configuration is not set" and all is well.

Are you capable to "select" the activity from the list of activities ?
There is an activity defined in AndroidManifest as the main activity (launcher)

If it shows Edit configuration Screen and Error as "Default activity not found" then go to your manifest file and in activity tag which will be your launching activity name should be like "packageName.MainActivty" instead of ".MainActivity" see below code for your reference
<activity
android:name="com.your.package.name.YourActivity"
android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>

Android Studio intermittent ClassNotFoundException

I've already read serveral Q&A's from SO and did not found a solution.
My problem is: I run my app from AndroidStudio and get the error bellow, then I run gradlew clean installDebug and code works just fine (outside AS, with NO changes).
I did NOT forgot to include my activity into AndroidManifest.
10-13 13:36:18.261 1457-1457/my.package E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: my.package, PID: 1457
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{my.package/my.package.activity.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "my.package.activity.MainActivity" on path: DexPathList[[zip file "/data/app/my.package-1.apk"],nativeLibraryDirectories=[/data/app-lib/my.package-1, /system/lib]]
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.ClassNotFoundException: Didn't find class "my.package.activity.MainActivity" on path: DexPathList[[zip file "/data/app/my.package-1.apk"],nativeLibraryDirectories=[/data/app-lib/my.package-1, /system/lib]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)
I'm using Android Studio 0.8.12 and this is reproducible with real devices and emulator (Genymotion).
EDIT
I've tried both "full path" and "class name only" into my AndroidManifest file to declare activities. And it still doesn't explain (IMHO) why it works via command line with gradle.

NullPointerException in ContextWrapper.getResources()

I really don't know what's going on with the Android app I'm building. At some point on its development, I started getting it breaking as soon as it starts in the emulator, with the message "Foo stopped". Here is the error log, if anyone could help me:
07-05 21:13:30.063 7647-7647/root.fazerumsom E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: root.fazerumsom, PID: 7647
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{root.fazerumsom/root.fazerumsom.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.content.ContextWrapper.getResources(ContextWrapper.java:89)
at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:78)
at root.fazerumsom.MainActivity.<init>(MainActivity.java:31)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1208)
at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)

You're calling getResources() from a field initializer. Something like
private String mStr = getResources().getString(...);
(or with drawables or other kind of resources).
This is not valid, since the Context isn't set up yet. Move this assignment inside the onCreate() method.

The checked exception java.lang.NullPointerException is thrown when you're trying to use an object without reference,in simple words that means: you're trying to use a object variable without value.
Remember that a variable hold bits, primitive and non-primitive variable do, but the difference is that primitive variable hold the value in bits, but non-primitive variable hold the bits (like a direction) to access the object in memory, and when it's not being used anymore GGC (Garbage Colector) kills it.