OK, so the problem I'm having occurs when the startGame button is pressed. The app crashes when the button is pressed. The activity is instantiated in the manifest so I'm not sure where the error is. The code for the intent is a copy of the other one (which works) so I have no clue where I went wrong.
Error Log:
02-25 14:46:51.064: E/AndroidRuntime(1261): FATAL EXCEPTION: main
02-25 14:46:51.064: E/AndroidRuntime(1261): Process: com.example.hegemony, PID: 1261
02-25 14:46:51.064: E/AndroidRuntime(1261): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.hegemony/com.example.hegemony.PlayerTurn}: java.lang.NullPointerException
Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hegemony"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="11"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.hegemony.SplashScreen"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.hegemony.StartScreen" >
<intent-filter>
<action android:name="com.example.hegemony.STARTSCREEN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.hegemony.SetupHomeScreen" >
<intent-filter>
<action android:name="com.example.hegemony.SETUPHOMESCREEN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.hegemony.SetupPlayer"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.example.hegemony.SETUPPLAYER" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.hegemony.PlayerTurn"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.example.hegemony.PLAYERTURN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
Java Code of sending activity:
public class SetupHomeScreen extends Activity{
private ArrayList<Player> p = GameMaster.players;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_setup_home_screen);
getActionBar().hide();
updatePlayers();
Button gotoInput = (Button) findViewById(R.id.btnSetupPlayer);
gotoInput.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent toInput = new Intent("com.example.hegemony.SETUPPLAYER");
startActivity(toInput);
}
});
Button startGame = (Button) findViewById(R.id.btnStartGame);
startGame.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent toStart = new Intent("com.example.hegemony.PLAYERTURN");
startActivity(toStart);
}
});
}
public void updatePlayers(){
TextView playerList = (TextView) findViewById(R.id.playerList);
String msg = "";
for(int i=0;i < p.size();i++)
msg = msg + "\n - "+p.get(i).getName();
playerList.setText(msg);
if(p.size() >=2){
Button enable = (Button) findViewById(R.id.btnStartGame);
enable.setEnabled(true);
}
}
}
Java code of receiving activity:
public class PlayerTurn extends Activity {
final ActionBar actionBar = getActionBar();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_player_turn);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
ActionBar.TabListener tabListener = new ActionBar.TabListener() {
#Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
#Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
}
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
};
}
}
Button startGame = (Button) findViewById(R.id.btnStartGame);
startGame.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent toStart = new Intent(SendingActivity.this, NewActivity.class);
startActivity(toStart);
}
});
I think this is how you should start an intent. Maybe its missing a context or the "activityname" is not the right way to do it. I tried to start an activity the way you are trying and it gave me an error as well, not the same one, but it didn't work.
I'm sorry if the solution I'm trying to provide doesn't work. This is really the first time I'm trying to help someone. I hope it works.
As per the logcat error message, your activity class is failing to instantiate. Instantiation involves the allocation and assignment of any class member variables. In the case of PlayerTurn, the only one is this:
final ActionBar actionBar = getActionBar();
The call to getActionBar() throws a NullPointerException because the activity's window has not been built yet - you should call getActionBar() after setContentView() has been called in onCreate(). You can resolve this by simply moving that line of code into onCreate().
If you still want to retain this as a class member variable, declare it but don't assign it:
ActionBar actionBar;
...and then do the assignment in onCreate():
actionBar = getActionBar();
Related
I have just gotten into Android app development and have been working on parts of my project in bits and pieces.
I first created my onboarding screens and then made my animated splash screen. However, when I run my application my splash screen does not show and instead loads the onboarding pages first. How can I fix this to make my app first transition through the splash screen before moving on the onboarding screens?
This is my SplashActivity Class code
public class SplashActivity extends AppCompatActivity {
private static int SPLASH_SCREEN = 5000;
// Variables
Animation topAnim;
ImageView image;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_splash);
// Animations
topAnim = AnimationUtils.loadAnimation(this,R.anim.top_animation);
// Hooks
image = findViewById(R.id.splashScreenLogo);
image.setAnimation(topAnim);
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
Intent intent = new Intent(SplashActivity.this, OnboardingActivity.class);
startActivity(intent);
finish();
}
}, SPLASH_SCREEN);
}
}
This is my OnboardingActivity Class code
public class OnboardingActivity extends AppCompatActivity {
private OnboardingAdapter onboardingAdapter;
private LinearLayout layoutOnboardingIndicators;
private MaterialButton buttonOnboardingAction;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_onboarding);
// Onboarding Screens
layoutOnboardingIndicators = findViewById(R.id.layoutOnboardingIndicators);
buttonOnboardingAction = findViewById(R.id.buttonOnboardingAction);
setupOnboardingItems();
final ViewPager2 onboardingViewPager = findViewById(R.id.onboardingViewPager);
onboardingViewPager.setAdapter(onboardingAdapter);
setupOnboardingIndicators();
setCurrentOnboardingIndicator(0);
onboardingViewPager.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
#Override
public void onPageSelected(int position) {
super.onPageSelected(position);
setCurrentOnboardingIndicator(position);
}
});
buttonOnboardingAction.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(onboardingViewPager.getCurrentItem() + 1 < onboardingAdapter.getItemCount()) {
onboardingViewPager.setCurrentItem(onboardingViewPager.getCurrentItem() + 1);
}
else {
startActivity(new Intent(getApplicationContext(), SignUpActivity.class));
finish();
}
}
});
}
}
Edit - My Manifest File
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.mentalhealthapp">
<application
android:allowBackup="true"
android:icon="#drawable/treen_app_logo"
android:label="treen"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".SplashActivity"></activity>
<activity android:name=".HomeActivity" />
<activity android:name=".SignInActivity" />
<activity android:name=".SignUpActivity" />
<activity android:name=".OnboardingActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
What should I change in my Manifest File?
You need to set the Launch activity as SplashActivity in your AndroidManifest.xml file
<activity
android:name=".SplashActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
I recently was studying making an AlarmReminder on youtube by this man's tutorial videos: DelaroyStudios.
Anyway... I followed his tutorial and made it work on a separate app. So next I modified it to the way I want my alarmreminder to be and tried to add it to my activity, however when I click the button routing to its activity launcher, it won't go off. By the way here's the repo: https://github.com/delaroy/AlarmReminder
I tried debugging but I can't see errors, so I really don't know where to start in fixing this part. But I suspect its on the dependencies on the gradle perhaps? or some other factor? Anyway please take a look at my code where I suspect the problem might be coming from.
Here's the manifests:
My Manifest
<application
android:name=".FireApp"
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name="com.loginpack.splash">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name="com.loginpack.LoginActivity" />
<activity android:name=".MainActivity" />
<activity android:name="com.Welcome.Welcome" />
<activity android:name="com.Welcome.CalendarActivity" />
<activity android:name="com.Welcome.Video" />
<activity android:name=".Profile" />
<activity android:name="com.Welcome.Image">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="image/*" />
</intent-filter>
</activity>
<activity android:name="com.alarmreminder.MainReminder">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity android:name="com.alarmreminder.AddReminderActivity"
android:label="#string/title_activity_add_reminder"
android:parentActivityName="com.alarmreminder.MainReminder"
android:theme="#style/AppTheme">
<!-- Parent activity meta-data to support 4.0 and lower -->
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.alarmreminder.MainReminder"
/>
</activity>
<activity android:name="com.Welcome.Info" />
<activity android:name=".Profile2" />
<activity android:name=".Profile3"/>
I checked the code and I suspect nothing except for some deprecated codes that were usually couldn't have affected the overall performance of the activity to the point that it can't even be opened and debugged. Please help me find a way to make this work. or perhaps if you know any method for me to debug activities without any errors showing. Oh and by the way this is what shows in the Verbose when I click on the activity.
Here's the code of the Activity mentioned:
public class MainReminder extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {
private FloatingActionButton mAddReminderButton;
private Toolbar mToolbar;
AlarmCursorAdapter mCursorAdapter;
AlarmReminderDbHelper alarmReminderDbHelper = new AlarmReminderDbHelper(this);
ListView reminderListView;
private static final int VEHICLE_LOADER = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_mainalarm);
mToolbar = findViewById(R.id.toolbar);
setSupportActionBar(mToolbar);
mToolbar.setTitle(R.string.app_name);
reminderListView = findViewById(R.id.list);
View emptyView = findViewById(R.id.empty_view);
reminderListView.setEmptyView(emptyView);
mCursorAdapter = new AlarmCursorAdapter(this, null);
reminderListView.setAdapter(mCursorAdapter);
reminderListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
Intent intent = new Intent(MainReminder.this, AddReminderActivity.class);
Uri currentVehicleUri = ContentUris.withAppendedId(AlarmReminderContract.AlarmReminderEntry.CONTENT_URI, id);
// Set the URI on the data field of the intent
intent.setData(currentVehicleUri);
startActivity(intent);
}
});
mAddReminderButton = findViewById(R.id.fab);
mAddReminderButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(v.getContext(), AddReminderActivity.class);
startActivity(intent);
}
});
getLoaderManager().initLoader(VEHICLE_LOADER, null, this);
}
#Override
public Loader<Cursor> onCreateLoader(int i, Bundle bundle) {
String[] projection = {
AlarmReminderContract.AlarmReminderEntry._ID,
AlarmReminderContract.AlarmReminderEntry.KEY_TITLE,
AlarmReminderContract.AlarmReminderEntry.KEY_DATE,
AlarmReminderContract.AlarmReminderEntry.KEY_TIME,
AlarmReminderContract.AlarmReminderEntry.KEY_REPEAT,
AlarmReminderContract.AlarmReminderEntry.KEY_REPEAT_NO,
AlarmReminderContract.AlarmReminderEntry.KEY_REPEAT_TYPE,
AlarmReminderContract.AlarmReminderEntry.KEY_ACTIVE
};
return new CursorLoader(this, // Parent activity context
AlarmReminderContract.AlarmReminderEntry.CONTENT_URI, // Provider content URI to query
projection, // Columns to include in the resulting Cursor
null, // No selection clause
null, // No selection arguments
null); // Default sort order
}
#Override
public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
mCursorAdapter.swapCursor(cursor);
}
#Override
public void onLoaderReset(Loader<Cursor> loader) {
mCursorAdapter.swapCursor(null);
}
}
PS: In the my manifest I didn't make it as the main launcher, since its only an activity after all.
I am trying to setup multiple buttons but I seem to be having trouble doing it. I have 2 onClickListener functions in the same activity. Am I right in doing this or should this be done some other way? btnChpt3 works but when I input the onclicklistener for btnChpt3_1 it force closes as soon as it opens. Thanks.
MainMenu.java
package com.th3ramr0d.learnar670_1;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainMenu extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button chapterThree = (Button) findViewById(R.id.btnChpt3);
chapterThree.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent(MainMenu.this, Chapter3.class));
}
});
Button chapterThree_1 = (Button) findViewById(R.id.btnChpt3_1);
chapterThree_1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent(MainMenu.this, Chapter3_1.class));
}
});
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
}
}
So I added a new class to handle the buttons on a sub menu page. But now I am running into the same problem I was previously where the button wont open. I am guessing its because the code isnt being ran for some reason.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.th3ramr0d.learnar670_1"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="21" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".MainMenu"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".SubMenuChapter3"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".Chapter3"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.th3ramr0d.learnar670_1.CHAPTER3" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Chapter4"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.th3ramr0d.learnar670_1.CHAPTER4" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
You can see here that my .MainMenu launches. I am guessing that means it launches at startup. So the button works. However, now I want the button associated with .SubMenuChapter3 to launch and it does nothing. Here Program runs with no errors but button wont open you can see I had the same problem until codepg was nice enough to tell me where I was wrong. But I want to use several of these sub menus so how would I do that?
Your problem, after reading, is that you are referencing a button that you have created in another layout which you are not inflating.
In the setContentView(R.layout.activity_main); you are inflating activity_main so you can only have onclick listeners for buttons and elements in that xml.
Make sure that you add btnChpt3 in this xml or if this button is supposed too be in another layout then have another activity or fragment control that layout by inflating it.
Right now this method Button chapterThree = (Button) findViewById(R.id.btnChpt3); is returning a null pointer exception.
I can see from your comments that you are inflating the view activity_main but Button with id bthChpt3_1 is in another file. This is an error as you can use findViewById(R.id.buttonId) to find the id of a button which exists within the view you are using. Since the button is in another xml file, it will throw a null pointer exception.
I'm a beginner android developer here and I coded a basic activity that loads an image, waits for 5 seconds and opens the main activity that holds a text view. There are no errors and it compiles perfectly fine. When I launch on my device though, it doesn't open. (Doesn't open on the emulator either).
I'm not sure why this is.
Here is the manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.gui"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme"
android:debuggable="true">
<activity
android:name="com.example.gui.MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.gui.Splash"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.SPLASH" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
Here is the Splash activity I intent to load first.
package com.example.gui;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
public class Splash extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.splash);
Thread splash_thread = new Thread(){
public void run(){
try{
sleep(5000);
} catch(InterruptedException e)
{ e.printStackTrace();
}finally{ Intent splash_intent = new Intent("android.intent.action.MAIN");
startActivity(splash_intent);
}
}
};
splash_thread.start();
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
finish();
}
}
And here is the other activity I intend to run:
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
I'm following a tutorial off the internet, this still doesn't run for some reason. My layout's are very standard as well. Help'd be appreciated.
You can set wrong path in manifest.xml file.
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme"
android:debuggable="true">
<activity
android:name="com.example.gui.Splash"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.gui.MainActivity"
android:label="#string/app_name" >
try this and now your splash screen lauch first and the main activity will launch...
if it not working then try this code only if your activity will not give response.
public class Splash_screen extends Activity {
private static String TAG = Splash_screen.class.getName();
private static long SLEEP_TIME = 3; // Sleep for some time
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE); // Removes title bar
this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); // Removes notification bar
setContentView(R.layout.splash_screen);
IntentLauncher launcher = new IntentLauncher();
launcher.start();
}
private class IntentLauncher extends Thread{
#Override
/**
* Sleep for some time and than start new activity.
*/
public void run() {
try {
// Sleeping
Thread.sleep(SLEEP_TIME*1000);
} catch (Exception e) {
Log.e(TAG, e.getMessage());
}
// Start main activity
Intent intent = new Intent(Splash_screen.this,Login_screen.class);
startActivity(intent);
finish();
}
}
I am still learning to code, but apps i code persistently can't work on 2 diferent devices. Can Eclipse (latest android sdk) be the error or i code wrong every single app?
Its force close on 2 devices
public class MainActivity extends Activity {
Button dugme = (Button) findViewById(R.id.dugme);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dugme.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
Cao();
}
});
}
private void Cao(){
Intent Cao = new Intent(this, Cao.class);
startActivity(Cao);
}}
This is Cao class
public class Cao extends Activity{
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.cao);
}}
And Manifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.book1"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.book1.MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.book1.Cao"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.Action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application></manifest>
Try to put
Button dugme = (Button) findViewById(R.id.dugme);
this line in your onCreate method. A class shoud have only variables and methods. This line is definition. So I think that is only problem in your code. Other than there is nothing wrong in your code.
Put this line
Button dugme = (Button) findViewById(R.id.dugme)
After
setContentView(R.layout.activity_main)
Android takes each reference of view_id according to its each layout xml
Think if android takes view reference_id before setting up layout to the given activity then we can not even keep same name of view ID for two different layout xml .
This line is wrong:
Button dugme = (Button) findViewById(R.id.dugme);
not because it not located in the onCreate method, but because it appears before this line:
setContentView(R.layout.activity_main);
And the reason for that is: if you didn't set your layout as the content view of your activity you can't use the findViewById method, because there is no place that this view could be found (you layout is not yet set).