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Context Null Pointer when starting intent [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 2 years ago.
Hi i am new to android studio and I am trying to start a new activity - however, I am having endless issues with getting Context - I have tried a few different methods posted on stack overflow but It just keeps throwing a null pointer please help. See onCreate method and exception below.
AddRoutine.class is just a blank activity
MainActivity
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MainActivity.mContext = this.getApplicationContext();
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
//Add Routine
FloatingActionButton fab = findViewById(R.id.addRoutine);
fab.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
startActivity(new Intent(MainActivity.this, AddRoutine.class));
}
});
generateRoutineListing(getAppContext());
//if returnListing.length > 0
// recyclerView.addItems
//else
// Show Jumbotron/Message board explaining that no routines have been created
}
Exception
E/AndroidRuntime: FATAL EXCEPTION: main
Process: za.co.freelanceweb.routines, PID: 14648
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ComponentName.<init>(ComponentName.java:130)
at android.content.Intent.<init>(Intent.java:5780)
at za.co.freelanceweb.routines.MainActivity$1.onClick(MainActivity.java:38)
at android.view.View.performClick(View.java:6294)
at android.view.View$PerformClick.run(View.java:24774)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6518)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Thanks so Much

Instead of:
MainActivity.mContext = this.getApplicationContext();
Use:
Context mcontext = MainActivity.this; //Also, set mcontext as a global variable.
Also,
Instead of:
generateRoutineListing(getAppContext());
Use:
generateRoutineListing(mcontext);

The problem is probably in this line:
MainActivity.mContext = this.getApplicationContext();
Activity extends Context so you can always use this to refer to the activity's context.
I am not sure what you are trying to do with that but you should not be using the application's context on one activity. The application context lives through out the entire lifetime of the application.
If you want want to start a new activity do this.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Intent intent = new Intent(this, AddRoutineActivity.class);
startActivity(intent);
}
And then register AddRoutineActivity in your AndroidManifest.xml file like so:
<activity android:name=".AddRoutineActivity" />
If you are new to android you may want to check out Kotlin.

Null point Exception error in MapBlocks Android

I am trying to follow This tutorial
and I am getting an error
This is the stack trace
Process: com.example.mapp, PID: 7624
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mapp/com.example.mapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.mapbox.mapboxsdk.maps.MapView.onCreate(android.os.Bundle)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.mapbox.mapboxsdk.maps.MapView.onCreate(android.os.Bundle)' on a null object reference
at com.example.mapp.MainActivity.onCreate(MainActivity.java:21)
This the mapview part of activity_main.xml
<com.mapbox.mapboxsdk.maps.MapView
android:id="#+id/mapView"
android:layout_width="match_parent"
android:layout_height="match_parent"
mapbox:mapbox_cameraTargetLat="37.7747"
mapbox:mapbox_cameraTargetLng="-122.4443"
mapbox:mapbox_styleUrl="mapbox://styles/mapbox/streets-v10"
mapbox:mapbox_cameraZoom="12"
/>
and this is complete MainActivity.Java ( Removed all the imports + few more functions of map box)
public class MainActivity extends AppCompatActivity {
private MapView mapView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Mapbox.getInstance(this, getString(R.string.access_token) );
mapView = (MapView) findViewById(R.id.mapView);
mapView.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
protected void onStart() {
super.onStart();
mapView.onStart();
}
#Override
protected void onResume() {
super.onResume();
mapView.onResume();
}
#Override
protected void onDestroy() {
super.onDestroy();
mapView.onDestroy();
}
}
I tried the following links but they didn't work link 1 link 2 link 4
Thanks in advance.

That YouTube video you're following is a bit old. Setting up a simple MapView is now done differently. For example, you can't set a map style URL via XML anymore.
https://docs.mapbox.com/android/maps/examples/create-a-simple-map-view shows the basic way to set up a Mapbox map.

Error: Attempt to invoke virtual method ... on a null object reference

Although this question has been asked several times none of the solutions has worked for me. I keep getting this error suddenly, and I think I might have have a problem different those others.
Here's the class thats responsible:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_car);
}
NumberFormat currencyFormatter = NumberFormat.getCurrencyInstance();
PageDownloader PDL = new PageDownloader();
TextView tv1 = findViewById(R.id.textView6);
TextView tv2 = findViewById(R.id.textView5);
TextView tv3 = findViewById(R.id.textView3);
public int Distance;
public int Mileage;
float GasPriceMid;
float GasPricePre;
float GasPriceReg;
public float Toll;
public float Parking;
String StringPriceReg;
String StringPriceMid;
String StringPricePre;
As well as this one:
public class MenuActivity extends AppCompatActivity {
PriceCalculator PC = new PriceCalculator();
//PageDownloader PDL = new PageDownloader();
EditText et1 = findViewById(R.id.et1);
EditText et2 = findViewById(R.id.et2);
EditText et3 = findViewById(R.id.et3);
EditText et4 = findViewById(R.id.et4);
It was simply supposed to create a reference to these objects but its receiving this error:
Process: com.example.ojd.pricecalculatorapp, PID: 5067
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.ojd.pricecalculatorapp/com.example.ojd.pricecalculatorapp.MenuActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3135)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3418)
at android.app.ActivityThread.access$1100(ActivityThread.java:231)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1823)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7422)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImpl.<init>(AppCompatDelegateImpl.java:249)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
at com.example.ojd.pricecalculatorapp.PriceCalculator.<init>(PriceCalculator.java:19)
at com.example.ojd.pricecalculatorapp.MenuActivity.<init>(MenuActivity.java:9)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3125)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3418) 
at android.app.ActivityThread.access$1100(ActivityThread.java:231) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1823) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:7422) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
It says that the problem was (PriceCalculator.java:19) which is
TextView tv1 = findViewById(R.id.textView6);
and (MenuActivity.java:9)
PriceCalculator PC = new PriceCalculator();
Thanks in advance and I'm hoping the answer won't just be a stupid mistake I made.

It's hard to tell from your code snippet, but PriceCalculator appears to extend from AppCompatActivity. You should never use the new operator with activities. Doing this will cause the activity to not have the proper context set and you won't be able to use methods like findViewById(). I'm not sure why MenuActivity has an instance of another activity inside of it. This is also a bad idea, activities should never have references to each other and should instead communicate through intents. Fixing these two issues should make things work better.

I think TextView tv1 = findViewById(R.id.textView6); should be in the onCreate method...
Try putting those in the onCreate method?

Just put all your identifications inside your Activity onCreate function. Meaning to say,
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_car);
TextView tv1 = findViewById(R.id.textView6);
TextView tv2 = findViewById(R.id.textView5);
TextView tv3 = findViewById(R.id.textView3);
}

App crashes when attempting to swap activities [duplicate]

This question already has answers here:
findViewByID returns null
(33 answers)
Closed 3 years ago.
This is a basic activity swapping.
The app does not crash if i declare a local button inside the configureActivitySwap() method like this:
Button voiceBtn = (findViewById(R.id.goToVoice));
But I have to declare the button in the global scope instead so I can use the button in other methods, mainly activating and deactivating the button when it should/should not be pressed.
I also noticed that if I remove the finish(); method and replace it with something else the app functions normally, but I have to have the finish(); method one way or another.
public class RecogActivity extends AppCompatActivity {
private Button voiceBtn;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
voiceBtn = findViewById(R.id.goToVoice);
setContentView(R.layout.main_layout);
// some unrelated code
configureActivitySwap();
}
public void configureActivitySwap(){
// Button voiceBtn = (findViewById(R.id.goToVoice));
voiceBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
finish();
}
});
}
}
My runtime error logs:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: tk.gandriks.gaaudiotransform, PID: 23125
java.lang.RuntimeException: Unable to start activity ComponentInfo{tk.gandriks.gaaudiotransform/tk.gandriks.gaaudiotransform.RecogActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2957)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6944)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at tk.gandriks.gaaudiotransform.RecogActivity.configureActivitySwap(RecogActivity.java:140)
at tk.gandriks.gaaudiotransform.RecogActivity.onCreate(RecogActivity.java:124)
at android.app.Activity.performCreate(Activity.java:7183)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1220)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2910)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) 
at android.os.Handler.dispatchMessage(Handler.java:105) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6944) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374) 

You need to call the setContentView() before calling voiceBtn = findViewById(R.id.goToVoice); Since you don't specify the layout the findViewById method will not get the button instance
public class RecogActivity extends AppCompatActivity {
private Button voiceBtn;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// set the layout first
setContentView(R.layout.YOUR_LAYOUT_XML_FILE_NAME)
voiceBtn = findViewById(R.id.goToVoice);
// some unrelated code
configureActivitySwap();
}
public void configureActivitySwap(){
// Button voiceBtn = (findViewById(R.id.goToVoice));
voiceBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
finish();
}
});
}

Try I guess) In your // some unrelated code is contains setContentView method?
public class RecogActivity extends AppCompatActivity {
private Button voiceBtn;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
voiceBtn = findViewById(R.id.goToVoice);
setContentView(R.layout.some_layout)
// some unrelated code
configureActivitySwap();
}
public void configureActivitySwap(){
// Button voiceBtn = (findViewById(R.id.goToVoice));
voiceBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
finish();
}
});
}
}
You caught NPE because of findViewById is calling on inflated view. You are have been calling findViewById before setContentView in the first case and got the exception. And in the second case - in configureActivitySwap, that going after setContentView. Move setContentView after super.onCreate(savedInstanceState) and all will be working fine.

Are you setting layout before trying to find view with findViewById?
setContentView(R.layout.main_layout);

voiceBtn = (Button) findViewById(R.id.goToVoice);
replace the statement in your onCreate() method with the above. It should work.
and use
super.finish() instead of finish()

Android: Can't access static elements outside Fragment class

I am trying to change elements such TextViews etc. that are parts of the Fragment (which is used for SlidingTabLayout). I can access TextView from the Tab1 class:
public class Tab1 extends Fragment {
public static TextView serverName;
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.tab_1,container,false);
serverName = (TextView) view.findViewById(R.id.serverName);
serverName.setText("This works, but I can't change text from outside the Tab1 class");
return view;
}
But when I want access the serverName TextView from anywhere I am always getting null value. Here I am trying to change the text from the activity which contains Sliding Tabs (Tab1 is a part of it):
public class Dashboard2 extends AppCompatActivity {
Toolbar toolbar;
ViewPager pager;
ViewPagerAdapter adapter;
SlidingTabLayout tabs;
CharSequence tabsTitles[] = {"Info", "Options"};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_dashboard2);
InitializeToolbarAndTabs();
Tab1.serverName.setText("This doesn't work");
}
private void InitializeToolbarAndTabs()
{
toolbar = (Toolbar) findViewById(R.id.tool_bar);
setSupportActionBar(toolbar);
adapter = new ViewPagerAdapter(getSupportFragmentManager(), tabsTitles, tabsTitles.length);
pager = (ViewPager) findViewById(R.id.pager);
pager.setAdapter(adapter);
tabs = (SlidingTabLayout) findViewById(R.id.tabs);
tabs.setDistributeEvenly(true);
tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
#Override
public int getIndicatorColor(int position) {
return getResources().getColor(R.color.tabsScrollColor);
}
});
tabs.setViewPager(pager);
}
}
Logs from the Android Studio:
java.lang.RuntimeException: Unable to start activity ComponentInfo{ASD.Dashboard2}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3119)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3218)
at android.app.ActivityThread.access$1000(ActivityThread.java:198)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1676)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6837)
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:1404)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at ASD.Dashboard2.onCreate(Dashboard2.java:54)
at android.app.Activity.performCreate(Activity.java:6500)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1120)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3072)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3218)
at android.app.ActivityThread.access$1000(ActivityThread.java:198)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1676)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6837)
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:1404)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference - how to solve this problem?

Not sure what you are doing but you can always find your fragment by FragmentManage.findFragmentByTag() or FragmentManager.findFragmentById().
Once found just access your field.

I don't think you have initialized the Tab1 fragment, at least I can't see it there.
Accessing fragment variables from an Activity through static declarations is a horrible idea, use voids in the fragment class.

I am sorry, the error you are getting is not related with accessing or not a static object of the Fragment. The error you are receiving is because at the moment you call Tab1.serverName.setText("This doesn't work"); your fragment still didnt inflate the view or still didn't charge the TextView (didn't arrive yet to serverName = (TextView) view.findViewById(R.id.serverName);). The fragments are charged into the view in a asynchrounous way, so even if you declare it in your layout as a tag, it may be possible that the Fragment's view is still not fully loaded.
If you absolutely want to be sure the fragment's view is fully loaded, use the protected void onResumeFragments() method:
#Override
protected void onResumeFragments() {
super.onResumeFragments();
Tab1.serverName.setText("This doesn't work");
}
Anyway, I strongly recommend you NOT to access fragment objects statically, but to use the findFragmentById() or findFragmentByTag() methods and then to access a public method inside the given fragment.
Hope it helps.