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App crashes when I call a constructor in an Activity

I am new to android studio and I am trying to build a Notepad app.
button.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v) {
String title = findViewById(R.id.textView3).toString();
String note_content = findViewById(R.id.textView).toString();
FileOutputStream outputStream;
try
{
outputStream = openFileOutput(title, Context.MODE_PRIVATE);
outputStream.write(note_content.getBytes());
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
MainActivity mainActivity = new MainActivity(title);
}
});
This is the button a user clicks to save the note. Once the code saves the note, it should send the Title to MainActivity so that it can be sent to Recycleview Adapter - this will display it in viewholder as a text.
Presently, when I run the code, it crashes - however, when I remove the constructor, the app works fine.
( MainActivity mainActivity = new MainActivity(title);)
Error:
10-02 02:39:13.822 27279-27279/? D/AndroidRuntime: Shutting down VM
10-02 02:39:13.824 27279-27279/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.quicknote, PID: 27279
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.quicknote/com.example.quicknote.MainActivity}: java.lang.InstantiationException: java.lang.Class<com.example.quicknote.MainActivity> has no zero argument constructor
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2337)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.InstantiationException: java.lang.Class<com.example.quicknote.MainActivity> has no zero argument constructor
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1090)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5443) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
10-02 02:39:20.081 27279-27279/com.example.quicknote I/Process: Sending signal. PID: 27279 SIG: 9

As per the error message:
java.lang.InstantiationException: java.lang.Class has no zero argument constructor
A zero argument constructor is required for the Android system to instantiate an Activity. You should never be manually calling an Activity constructor yourself since only the system can properly create an Activity.
The Parcelables and Bundles documentation details the correct way of sending information to an Activity using the extras Bundle.

Unable to instantiate activity. Because you can't start an activity like this. You have to use intent to start activity. To sent "title" use intent extra.
Intent intent=new Intent(CurrentActivity.this, NewActivty.this);
intent.putExtra("title", title);
startActivty(intent);

Is your Activity in your AndroidManifest.xml?
If it is, you have to retrieve the title from your extras from onCreate() of MainActivity instead from the constructor.
Something like that:
//that code instead of your MainActivity mainActivity = new MainActivity(title); line
Intent intent = new Intent(YourActualActivity.this, MainActivity.class);
intent.putExtra("title", title);
startActivity(intent);
//That code in the onCreate method of your MainActivity
Bundle extras = getIntent().getExtras();
if (extras != null) {
String title = extras.getString("title");
}

App crashes when file is shared in Fragment

I have a Fragment which is attached to MainActivity. It displays an image. User has to share the image but the app crashes when clicking the share button.
This is the Fragment code:
Context mcontext = getActivity();
case R.id.item_share: {
final Uri uri = FileProvider.getUriForFile(mcontext, "com.whats.insta", file);
final Intent intent = ShareCompat.IntentBuilder
.from((Activity)mcontext)
.setType("image/jpg")
.setStream(uri)
.createChooserIntent()
.addFlags(Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET)
.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
mcontext.startActivity(intent);*/
break;
}
Crash log
09-05 10:41:05.410 26011-26011/com.whats.insta E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.whats.insta, PID: 26011
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.app.Activity.getPackageName()' on a null object reference
at android.support.v4.app.ShareCompat$IntentBuilder.<init>(ShareCompat.java:216)
at android.support.v4.app.ShareCompat$IntentBuilder.from(ShareCompat.java:210)
at com.whats.insta.ui.imageslider.imagedetails.ImageDetailsFragment.onOptionsItemSelected(ImageDetailsFragment.java:267)
at android.support.v4.app.Fragment.performOptionsItemSelected(Fragment.java:2476)
at android.support.v4.app.FragmentManagerImpl.dispatchOptionsItemSelected(FragmentManager.java:3343)
at android.support.v4.app.FragmentController.dispatchOptionsItemSelected(FragmentController.java:347)
at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:413)
at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:195)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
at android.support.v7.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:63)
at android.support.v7.widget.Toolbar$1.onMenuItemClick(Toolbar.java:203)
at android.support.v7.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:780)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:822)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:171)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:973)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:963)
at android.support.v7.widget.ActionMenuView.invokeItem(ActionMenuView.java:624)
at android.support.v7.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:150)
at android.view.View.performClick(View.java:6261)
at android.widget.TextView.performClick(TextView.java:11185)
at android.view.View$PerformClick.run(View.java:23752)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6776)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)

You must check if the implicit intent resolves to at least one activity otherwise application crashes.
// Verify the intent will resolve to at least one activity
if (mContext != null && intent.resolveActivity(getPackageManager()) != null) {
startActivity(chooser);
}

NullPointerException while dealing with creating an intent in MainActivity [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
I've been looking into this for a few days and can't seem to find a thread specific to my problem. My app crashes every time I try to add a string to my bundle.
I'm getting the error at extras.putString(EXTRA_MESSAGE, message);
MainActivity.java
public class MainActivity extends AppCompatActivity {
private ArrayList<String> priceGroupSpinnerItems;
public static final String EXTRA_MESSAGE = "lss.mywebsiteoffline.MESSAGE";
public String message = "";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Spinner spnPriceGroup = (Spinner) findViewById(R.id.price_group_spinner);
ArrayAdapter adapter = ArrayAdapter.createFromResource(this, R.array.list_price_group, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spnPriceGroup.setAdapter(adapter);
message = spnPriceGroup.getSelectedItem().toString();
}
/** Called when the user taps the Go button */
public void sendMessage(View view) {
Intent mIntent;
mIntent = new Intent(this, nextActivity.class);
Bundle extras = mIntent.getExtras();
extras.putString(EXTRA_MESSAGE, message);
mIntent.putExtras(extras);
startActivity(mIntent);
}
}
Logcat
E/AndroidRuntime: FATAL EXCEPTION: main
Process: lss.mybbofflinever3, PID: 8181
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:5702)
at android.widget.TextView.performClick(TextView.java:10896)
at android.view.View$PerformClick.run(View.java:22546)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5702) 
at android.widget.TextView.performClick(TextView.java:10896) 
at android.view.View$PerformClick.run(View.java:22546) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7224) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$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 'void android.os.Bundle.putString(java.lang.String, java.lang.String)' on a null object reference
at lss.mywebsiteoffline.MainActivity.sendMessage(MainActivity.java:59)
I have tried examples to use just intent, or bundle, and adding strings directly to putString. I might be missing something blatantly obvious. Not sure what I might be looking for after adding strings directly to the putString method and getting the same error.

By default an Intent does not have extras and getExtras() returns null. If you want to set extras, you need to create the extras bundle yourself. Replace
Bundle extras = mIntent.getExtras();
with
Bundle extras = new Bundle();
Or just call one of the putExtra() overloads on the Intent - it will also init the extras bundle in case it's not there already.

Try this:
Intent mIntent = new Intent(this, nextActivity.class);
mIntent.putExtra(EXTRA_MESSAGE, message);
startActivity(mIntent);

app crash with android.content.Context.getPackageName()' on a null object reference

i need help.
I'm in the finish phase of development of my android application and now after a few month of develop the app magically crash with this error :
java.lang.String android.content.Context.getPackageName()' on a null object reference
I don't know what is the problem but i will post the code that cause the crash :
public static void start(Context context) {
context.startActivity(new Intent(context, ConversationsActivity.class));
}
called with this piece of code (inside a fragment):
ConversationsActivity.start(getActivity());
The last change that i've make was to add Fabric.io ( in particular Branch ) and from the history in the last commit on git i don't show nothing that can produce this error
EDIT :
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:128)
at android.content.Intent.<init>(Intent.java:4900)
at com.exampleapp.views.messages.ConversationsActivity.start(ConversationsActivity.java:31)
at com.exampleapp.views.menu.MenuFragment.onMenuMessagesClicked(MenuFragment.java:116)
at com.exampleapp.views.menu.MenuFragment_ViewBinding$5.doClick(MenuFragment_ViewBinding.java:82)
at butterknife.internal.DebouncingOnClickListener.onClick(DebouncingOnClickListener.java:22)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Or you could do this:
public static void start(Activity activity) {
activity.startActivity(new Intent(activity, ConversationsActivity.class));
}

You should use getActivity() to launch an Activity from Fragment.
From a Fragment: Context is parent activity (getActivity()).
Intent intent = new Intent(getActivity(), ConversationsActivity.class);
startActivity(intent);
From an Activity: Context is current activity (this).
Intent intent = new Intent(this, ConversationsActivity.class);
startActivity(intent);

Your problem is that you are using the intent wrong. Replace your start() code with this:
public static void start() {
Intent i = new Intent(getApplicationContext(), ConversationsActivity.class);
startActivity(i);
}
Then instead of using ConversationsActivity.start(getActivity()); to call it, just use start(); when you want to call the method.
Hope this helps!

android.app.ActivityThread.getApplicationThread()' on a null object reference

The microhonePopUp method will work in MainActivity, but I'd like for it to work from another class (MediaButtonIntentReceiver). The problem is with startActivityForResult(intent, REQUEST_CODE); - but I don't know how to resolve it.
in the MainActivity class
public void microphonePopUp(){
Intent intent = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
intent.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL,
RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
intent.putExtra(RecognizerIntent.EXTRA_PROMPT, "Voice your answer");
startActivityForResult(intent, REQUEST_CODE);
}
in the MediaButtonIntentReceiver class
public class MediaButtonIntentReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
if (Intent.ACTION_MEDIA_BUTTON.equals(intent.getAction())) {
KeyEvent event = (KeyEvent)intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
if (KeyEvent.KEYCODE_HEADSETHOOK == event.getKeyCode()) {
MainActivity test = new MainActivity();
test.microphonePopUp();
}
}
}
}
12-09 11:20:14.803 19556-19556/com.timtennyson.priceaddition
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.timtennyson.priceaddition, PID: 19556
java.lang.RuntimeException: Unable to start receiver
com.timtennyson.priceaddition.MediaButtonIntentReceiver:
java.lang.NullPointerException: Attempt to invoke virtual method
'android.app.ActivityThread$ApplicationThread
android.app.ActivityThread.getApplicationThread()' on a null object
reference
at android.app.ActivityThread.handleReceiver(ActivityThread.java:3641)
at android.app.ActivityThread.access$2000(ActivityThread.java:221)
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1876)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual
method 'android.app.ActivityThread$ApplicationThread
android.app.ActivityThread.getApplicationThread()' on a null object
reference
at android.app.Activity.startActivityForResult(Activity.java:4283)
at android.app.Activity.startActivityForResult(Activity.java:4230)
at
android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:842)
at
com.timtennyson.priceaddition.MainActivity.microphonePopUp(MainActivity.java:103)
at
com.timtennyson.priceaddition.MediaButtonIntentReceiver.onReceive(MediaButtonIntentReceiver.java:27)
at android.app.ActivityThread.handleReceiver(ActivityThread.java:3634)
at android.app.ActivityThread.access$2000(ActivityThread.java:221) 
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1876) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7224) 
at java.lang.reflect.Method.invoke(Native Method)

NEVER create an instance of an activity, service, or provider yourself.
If your objective is to listen for ACTION_MEDIA_BUTTON broadcasts while MainActivity is visible:
Move MediaButtonIntentReceiver to be a nested class inside of MainActivity
Get rid of test from onReceive(), and just call microphonePopUp() (which I assume is a method on MainActivity)
Register your MediaButtonIntentReceiver using registerReceiver() in onStart() of MainActivity, and use unregisterReceiver() in onStop()
If your objective is to listen ACTION_MEDIA_BUTTON broadcasts at other points in time — by registering your receiver in the manifest — while you can do that, you cannot use microphonePopUp() from that receiver.