Develop Reference

NullPointerException on Intent between two Activities

I am trying to send an Intent value between two activities, though it appears, having read this, that in my second activity, the received intent is null; having encoutnered an NPE at runtime.
The intended functionality behind this is: 'the user scans a code in Activity A' -> 'a true value received and packed into an intent' -> 'Activity B opens, unpacks the intent and checks that the intent value is true' -> 'if true, the height of an ImageView in the activity is reduced by a set amount'.
I am therefore, not sure why my Intent is received as null in Activity B, as I would like this check to happen so that the height is updated when the activity opens?
Activity A:
//do the handling of the scanned code being true and display
//a dialog message on screen to confirm this
#Override
public void handleResult(Result result) {
final String myResult = result.getText();
Log.d("QRCodeScanner", result.getText());
Log.d("QRCodeScanner", result.getBarcodeFormat().toString());
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Activity Complete!");
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
//the user has pressed the OK button
#Override
public void onClick(DialogInterface dialog, int which) {
scannerView.resumeCameraPreview(QRActivity.this);
//pack the intent and open our Activity B
Intent intent = new Intent(QRActivity.this, ActivityTank.class);
intent.putExtra("QRMethod", "readComplete");
startActivity(intent);
}
});
builder.setMessage(result.getText());
AlertDialog alert1 = builder.create();
alert1.show();
}
Activity B:
// in onCreate, I check that the bundled intent is true
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tank);
if (savedInstanceState == null) {
Bundle extras = getIntent().getExtras();
if (extras == null) {
//then the extras bundle is null, and nothing needs to be called here
}
else {
String method = extras.getString("QRmethod");
if (method.equals("readComplete")) {
updateTank();
}
}
}
}
//this is the method that is called when the intent check is true
public int tHeight = 350;
public void updateTank() {
ImageView tankH = (ImageView)findViewById(R.id.tankHeight);
ViewGroup.LayoutParams params = tankH.getLayoutParams();
params.height = tHeight - 35;
tankH.setLayoutParams(params);
}

In Activity B you have a typo while pulling QRMethod from the Intent extras. You are using QRmethod while you have set extras with 'QRMethod'.

You can use :
In first activity ( MainActivity page )
Intent i = new Intent(MainActivity.this,SecondActivity.class);
i.putExtra("QRmethod","readComplete" );
then you can get it from your second activity by :
In second activity ( SecondActivity page )
Intent intent = getIntent();
String YourtransferredData = intent.getExtras().getString("QRmethod");

You can get string value by using intent.getStringExtra() method like this in your second activity.
if (getIntent() != null){
getIntent().getStringExtra("QRmethod") //this s your "readComplete" value
}

How to save the intent Extras in Shared prefrences

Here is my code which request user for their username:
private void request_user_name() {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Enter name:");
final EditText input_field = new EditText(this);
input_field.setText(sharedpreferences.getString("username",""));
final SharedPreferences.Editor editor = sharedpreferences.edit();
builder.setCancelable(false);
builder.setView(input_field);
final String savedName = sharedpreferences.getString(username,"");
input_field.setText(savedName);
input_field.setSelection(input_field.getText().length());
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialogInterface, int i) {
name = input_field.getText().toString();
if(TextUtils.isEmpty(savedName)) {
input_field.setError("Your message");
builder.setCancelable(false);
}
editor.putString(username, name);
editor.apply();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialogInterface, int i) {
if(TextUtils.isEmpty(savedName)) {
input_field.setError("Your message");
builder.setCancelable(false);
}
else
{
dialogInterface.cancel();
request_user_name();
}
}
});
builder.show();
}
And this is how I pass he username to next Activity:
intent.putExtra("room_name",((TextView)view).getText().toString() );
intent.putExtra("user_name",name);
intent.putExtra("default_name","anyonymous");
startActivity(intent);
And this is how I receive the Intent Extra in next Activity:
if (getIntent().getExtras() != null
&& getIntent().getExtras().get("user_name")!=null) {
user_name = getIntent().getExtras().get("user_name").toString();
}else{
user_name = getIntent().getExtras().get("default_name").toString();
}
My problem is when users don't enter his name and it returns null then it returns anyonymous but when users enter his name then it pass user name to next activity. But when I restart the app then again it passes anyonymous to next activity instead of usernae the user already entered
So I need suggestion on how to save the entered username in shared prefrences and use the same in future launch of app unless new name is not entered instead of anyonymous
Thanks in advance.

If you are already using SharedPreferences to store the user_name, then you don't need to pass the user_name via Intent. SharedPreferences are global and could be accessed throughout the application. Just do:
sharedpreferences.getString("username","anonymous")
in your target activity.

Shared Preferences not retrieving value

I have two activities namely Registration and Login where I defined a Shared Preferences in the Registration class. On the Registration page, if you click on the button that takes you to the Login Activity from the Registration Activity. I am storing a Shared Preferences value, so that on launching the app the second time, let the app immediately go to the LoginActivity instead of opening the first Activity which is Registration Activity. Here is my SharedPreferences class called Session.
private SharedPreferences prefs;
public Session(Context cntx) {
// TODO Auto-generated constructor stub
prefs = PreferenceManager.getDefaultSharedPreferences(cntx);
}
public void setusename(String usename) {
SharedPreferences.Editor editor = prefs.edit();
editor.putString("username", usename).commit();
editor.commit();
public Boolean contKey(String key){
if (prefs.contains(key)){
return true;
}else{
return false;
}
}
Here is the button in the RegstrationActivity that stores the SharedPreferences value before going to the LoginActivity so that on launch the second time, it opens the LoginActivity class
loginLink.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
session = new Session(getApplicationContext());
session.setusename("hello123");
Intent intent = new Intent(getApplication(),ActivityLogin.class);
startActivity(intent);
finish();
}
});
I have defined this in the onCreate method of RegistrationActivity class to switch to the ActivityLogin screen on next time the app is launched
System.out.println("it got here...2");
try {
if (session.contKey("username")) {
System.out.println("it got here...");
Intent intent = new Intent(getApplication(), ActivityLogin.class);
startActivity(intent);
overridePendingTransition(R.anim.enter, R.anim.exit);
finish();
} else {
System.out.println("it got here...3");
Intent intent = new Intent(getApplication(), ActivityRegistration.class);
startActivity(intent);
finish();
overridePendingTransition(R.anim.enter, R.anim.exit);
}
}catch(Exception ex){
}
Please why is my Shared Preferences not switching to the LoginActivity the second time the is launched. Kindly assist

TRy this
private SharedPreferences prefs;
public Session(Context cntx) {
// TODO Auto-generated constructor stub
prefs = PreferenceManager.getDefaultSharedPreferences(cntx);
}
public void setusename(String usename) {
SharedPreferences.Editor editor = prefs.edit();
editor.putString("username", usename);
editor.commit();
}
}
public String getusename() {
return prefs.getString("username","");
}
}
than use this way to get value SharedPreferences
session = new Session(getApplicationContext());
session.setusename("hello123");
String username=session.getusename();
Sample code
try {
if (!session.getusename().equals("")) {
System.out.println("it got here...");
Intent intent = new Intent(getApplication(), ActivityLogin.class);
startActivity(intent);
overridePendingTransition(R.anim.enter, R.anim.exit);
finish();
} else {
System.out.println("it got here...3");
Intent intent = new Intent(getApplication(), ActivityRegistration.class);
startActivity(intent);
finish();
overridePendingTransition(R.anim.enter, R.anim.exit);
}
}catch(Exception ex){
}

Instead of default shared preference, you can define a private one with your desired name in the Activity A..like as follows..
SharedPreferences preferences = getSharedPreferences("myPreferences",0);
SharedPreferences.Editor editor= preferences.edit();
editor.putString("userName","raju");
editor.commit();
If you want to retrieve that value from shared preferences in Activty A(I mean in the same activity), you can use following code..
String user_name= preferences.getString("userName","N/A");
or else in Activity B(I mean in some other activty), this time you don't need editor(for retrieval)..the code will be as follows
SharedPreferences preferences = getSharedPreferences("myPreferences",0);
String user_name= preferences.getString("userName","N/A");

Broadcastreceiver cannot receive when activity not opened

I have a notepad activity that opens up a window dialog version of it where user can go to another app and still type on the notepad
For both notepad to have the same content, I used broadcastReceiver to set the text of the notepad activity to the one in the dialog when the user is done.
Activity's BroadcastReceiver:
private BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
final globalVariable globalVariable = (globalVariable) getApplicationContext();
et_editor.setText(globalVariable.getScriptEditorText());
Toast.makeText(Script_editor.this, "Script Editor have been updated", Toast.LENGTH_SHORT).show();
}
};
Close Button of the Dialog:
btn_Close = (Button) view.findViewById(R.id.button_Close);
btn_Close.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
AlertDialog alertDialog = new AlertDialog.Builder(getApplicationContext())
.setTitle("Would you like to update the editor?")
.setNegativeButton("No, discard the changes", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
Toast.makeText(ColorCoordinatePickerService.this, "Changes have been discarded", Toast.LENGTH_SHORT).show();
dialog.dismiss();
stopSelf();
}
})
.setPositiveButton("Yes, update with changes", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
final globalVariable globalVariable = (globalVariable) getApplicationContext();
globalVariable.setScriptEditortext(CCEditor.getText().toString());
Intent intent = new Intent(BROADCAST_ACTION);
sendBroadcast(intent);
dialog.dismiss();
stopSelf();
}
})
.create();
alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
alertDialog.show();
}
});
It works BUT the user have to go back to the notepad activity (cannot be in another app or activity).
How do I update the notepad's content without having to "open" it up?

Queue the changes in BroadcastReceiver and when NotepadActivity resumes set the changes in the EditText. The queue doesn't need to be an actual queue, you can persist the last broadcast receiver data somewhere.

I am not sure, but it may be clear your global variable on moving from activity to another activity, also you are declaring the instance of global variable so it will set value in instance not in main variable and therefor you will not get it on receiver.
So I think you should set value in intent and then get it on receiver and manage it so it will work.
Check below, first your click event of dialog box method
#Override
public void onClick(DialogInterface dialog, int which) {
final globalVariable globalVariable = (globalVariable) getApplicationContext();
globalVariable.setScriptEditortext(CCEditor.getText().toString());
Intent intent = new Intent(BROADCAST_ACTION);
intent.putExtra("global_variable","" + CCEditor.getText().toString());
sendBroadcast(intent);
dialog.dismiss();
stopSelf();
}
And now get value in receiver as like below.
private BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
final globalVariable globalVariable = (globalVariable) getApplicationContext();
String strData = intent.getExtras().getString("global_variable");
et_editor.setText(strData);
Toast.makeText(Script_editor.this, "Script Editor have been updated", Toast.LENGTH_SHORT).show();
}
};
Hope this will work

without opening acitivity,you want to update data then only one way you can do it.when you receive in receiver set all data into sharepreference.Whenever your notepad activity opens you can set take data from sharepreference and set it into notepad activity.

Use LocalBroadcastManager.
Example: How to use it

Pass multiple Intents to multiple activities

I want to pass info as shown in this picture screen description
I know that my code is working, becuase with one Intent it works perfectley. However, when I try to put two or more Intents it seems to get messed up. I also checked here to find a sutibale solution, but I don't think I can use it the same way. Thanks in advance
--update--
still dosen't work
i did this on my saving side
Intent saveIntent = new Intent(this, MainActivity.class);
SharedPreferences.Editor editor = getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE).edit();
editor.putString("time", displayTime.getText().toString());
editor.commit();
startActivity(saveIntent);
and this on my reciving side
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
String time = preferences.getString("time",null);
if (time != null)
getTime.setText(time);
Main Activity:
private Button createNewEvent;
private Button showMyEvents;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
createNewEvent = (Button) findViewById(R.id.bCreateNewEvent);
showMyEvents = (Button) findViewById(R.id.bShowMyEvents);
}
public void buttonOnClick(View v) {
switch (v.getId()) {
case R.id.bCreateNewEvent:
Intent createNewEventIntent = new Intent(this, CreateNewEventActivity.class);
startActivity(createNewEventIntent);
break;
case R.id.bShowMyEvents:
Intent myEventsIntent = new Intent(this,MyEventsActivity.class);
startActivity(myEventsIntent);
break;
}
}
}
screen 1 save button:
case R.id.bSaveNewEvent:
Intent putIntent = new Intent(getApplicationContext(),MyEventsActivity.class);
// String text = displayTime.getText().toString();
putIntent.putExtra("time",displayTime.getText().toString());
Intent saveIntent = new Intent(this, MainActivity.class);
startActivity(saveIntent);
startActivity(putIntent);
screen 2 getExtras
public class MyEventsActivity extends AppCompatActivity {
TextView getTime;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_events);
getTime = (TextView) findViewById(R.id.tvGetTime);
Intent in = getIntent();
String name = in.getStringExtra("time");
getTime.setText(name);
/* Bundle extras = getIntent().getExtras();
if (extras != null){
getTime.setText(extras.getString("time"));
}*/

If you are trying to save data that will be need to be used in multiple other activities, SharedPreferences will be the easiest solution.
https://developer.android.com/training/basics/data-storage/shared-preferences.html
When you want to save a value, you would use:
SharedPreferences.Editor editor = getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE).edit();
editor.putString("time", displayTime.getText().toString());
editor.commit();
Then when you want to get the preference later on you would use:
SharedPreferences preferences = getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE);
String time = preferences.getString("time", "");