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On clicking button the app goes back to homepage

So I am new and working on an app, so I have created homepage of it and then when we click on anyone of it it opens a new activity in which when clicking the button to get the answer doesnt work and it goes back to the homepage. Please help me solve this!
This is my code of main activity
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
CardView Currency = (CardView) findViewById(R.id.Currency);
CardView Area = (CardView) findViewById(R.id.Area);
CardView Length = (CardView) findViewById(R.id.Length);
CardView Temperature = (CardView) findViewById(R.id.Temperature);
CardView Time = (CardView) findViewById(R.id.Time);
CardView Weight = (CardView) findViewById(R.id.Weight);
Currency.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Currency.class);
startActivity(intent);
}
});
Weight.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Weight.class);
startActivity(intent);
}
});
Time.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Time.class);
startActivity(intent);
}
});
Length.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Length.class);
startActivity(intent);
}
});
Area.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Area.class);
startActivity(intent);
}
});
Temperature.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Temperature.class);
startActivity(intent);
}
});
}
And this is of my new activity to open at homepage and convert the value
public class Weight extends AppCompatActivity {
private TextView textView;
private Button button;
private EditText editText;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_weight);
button = findViewById(R.id.button);
textView = findViewById(R.id.textView);
editText = findViewById(R.id.editText);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Toast.makeText(Weight.this, "Request Proceeded", Toast.LENGTH_SHORT).show();
String s = editText.getText().toString();
Integer.parseInt(s);
int kg = Integer.parseInt(s);
double pound = 2.205 * kg;
textView.setText("The corresponding value in Pound is" + pound);
}
});
}

How to store the login state in sharedpreferences

I'm making an Android app and in my app, I add the feature of storing the login state.
My Splash screen:
public class Splash extends AppCompatActivity {
private SharedPreferences preferences;
public int a = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash);
final ProgressBar progressBar = (ProgressBar) findViewById(R.id.progressbar);
new CountDownTimer(5000, 1000) {
#Override
public void onTick(long millisUntilFinished) {
a = a + 1;
progressBar.setProgress(a);
}
#Override
public void onFinish() {
SharedPreferences preferences = getSharedPreferences("login", MODE_PRIVATE);
String check = preferences.getString("login", "off");
if (check.equals("on")) {
startActivity(new Intent(Splash.this, Menu.class));
} else {
startActivity(new Intent(Splash.this, LoginPage.class));
}
}
}.start();
} }
My Login screen:
public class LoginPage extends AppCompatActivity {
private SharedPreferences preferences;
Context context;
Button login, register, database;
EditText username;
EditText password;
TextView msg;
MyDBManager db;
static final int REGISTRATION_REQUEST = 1; // The request code
#Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.loginpage);
db = new MyDBManager(this);
msg = (TextView) findViewById(R.id.msg);
login = (Button) findViewById(R.id.button);
register = (Button) findViewById(R.id.button2);
database = (Button) findViewById(R.id.button3);
username = (EditText) findViewById(R.id.user);
password = (EditText) findViewById(R.id.pass);
// Click and move to the next activity
login.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
db.open();
Cursor c = db.getUser(username.getText().toString(), password.getText().toString());
if (c.moveToFirst()) {
db.close();
context.startActivity(new Intent(context,Menu.class));
// Intent i=new Intent(getApplicationContext(),Menu.class); //
i.putExtra("Username", username.getText().toString()); //
startActivity(i); // call Login Activity
Store();
}
else
{
db.close();
// set error message when the username and/or password is not valid
msg.setText("Unable to login: wrong username or password!");
// Stay at the current activity.
}
}
private void Store() {
SharedPreferences preferences=context.getSharedPreferences("login",Context.MODE_PRIVATE);
SharedPreferences.Editor editor=preferences.edit();
editor.putString("login_status","on");
editor.commit();
}
});
// Click and move to the next activity
register.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(LoginPage.this, Registration.class);
startActivityForResult(intent, REGISTRATION_REQUEST);
}
});
// Click and move to the next activity
database.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(LoginPage.this, Database.class);
startActivity(intent);
}
});
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == REGISTRATION_REQUEST) {
//if(resultCode == Registration.RESULT_OK){
Log.d("Pikatchu", "User successfully registered!");
Bundle res = data.getExtras();
String result = res.getString("result");
System.out.println(result);
msg.setText(result);
}
}
}
My Menu screen:
public class Menu extends AppCompatActivity {
private SharedPreferences preferences;
Button startJourney, displayJourneys;
TextView msg; // where to display the name of the user
Button buttonLogout ;
/* the string is where to store data when we select something */
String db_username;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.menu);
buttonLogout = (Button) findViewById(R.id.btn_logout);
msg = (TextView) findViewById(R.id.msg);
startJourney = (Button) findViewById(R.id.recordingmode);
// Bundle bundle = getIntent().getExtras(); //
db_username = (bundle.getString("Username")); //// //// // Set
Welcome message to the user who logged in //
msg.setText("Welcome "+db_username);
// Click and move to the next activity // startJourney.setOnClickListener(new View.OnClickListener() { //
#Override // public void onClick(View v) { //
Intent intent = new Intent(Menu.this, Recordingmode.class); //
intent.putExtra("Username", db_username); //
startActivity(intent); // } // });
// Click and move to the next activity buttonLogout.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
SharedPreferences preferences=getSharedPreferences("login", Context.MODE_PRIVATE);
SharedPreferences.Editor editor=preferences.edit();
editor.putString("login_status","off");
editor.commit();
finish();
moveTaskToBack(true);
} });
}
}
But if I login in the app, the error is thrown:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null
object reference

Click Listeners to RecyclerView [duplicate]

This question already has answers here:
RecyclerView: how to catch the onClick on an ImageView?
(2 answers)
Closed 4 years ago.
What I am trying to accomplish is to create a listener for the ImageView inside the row of RecyclerView.
This code is working already, but this is not the solution that I wanted to have, because you need to double click the ImageView before getting the desired result.
// row click listener
recyclerView.addOnItemTouchListener(new RecyclerTouchListener(getApplicationContext(), recyclerView, new RecyclerTouchListener.ClickListener() {
#Override
public void onClick(View view, final int position) {
ImageView viewContent = (ImageView)view.findViewById(R.id.btnViewContent);
ImageView deleteContent = (ImageView)view.findViewById(R.id.btnDeleteContent);
viewContent.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(), "VIEW CONTENT", Toast.LENGTH_SHORT).show();
}
});
deleteContent.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(), "DELETE CONTENT", Toast.LENGTH_SHORT).show();
}
});
}
#Override
public void onLongClick(View view, int position) {}
}));
Any idea how to translate this into single click solution? Advice or even a single comment would help me a lot.

This is not the right way as one of our friend suggested onBindViewHolder is caleed again and again during scrolling so it is not the best practice to add listener there.
Best way is to add it on ViewHolder as I suggested. Check my answer above.
Add your imageView click listener in OnBindViewHolder method
#Override
public void onBindViewHolder(#NonNull final MyViewHolder holder, int position) {
holder.btnClassAddCart.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Do what you want here
}
});
}

Then there is no need to implement recyclerView.addOnItemTouchListener , inside Viewholder just add clicklistener on the view(image) you want below is the example for reference.
` public static class HeaderViewHolder extends RootViewHolder {
#BindView(R.id.cardview)
CardView cardview;
#BindView(R.id.main_container)
LinearLayout main_container;
#BindView(R.id.music_cardview)
CardView music;
#BindView(R.id.shabad_cardview)
CardView shabadvaani;
#BindView(R.id.news_cardview)
CardView news;
#BindView(R.id.donate_cardview)
CardView donate;
#BindView(R.id.bs_cardview)
CardView bs;
#BindView(R.id.bl_cardview)
CardView bl;
#BindView(R.id.bng_cardview)
CardView bng;
#BindView(R.id.more_cardview)
CardView more;
#BindView(R.id.vid_cardview)
CardView vid;
#BindView(R.id.medi_cardview)
CardView medi;
//
// #BindView(R.id.ama_cardview)
// CardView ama;
public HeaderViewHolder(final View itemView,final OnItemClickListener mOnItemClickListener) {
super(itemView);
ButterKnife.bind(this, itemView);
news.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (mOnItemClickListener != null) {
mOnItemClickListener.openDrawer();
}
//Intent i= new Intent(ctx,);
//open drawer code
}
});
shabadvaani.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(ctx, IndexActivity.class);
ctx.startActivity(i);
}
});
music.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(ctx, MainActivity.class);
i.putExtra("slug","audiobhajan");
ctx.startActivity(i);
//open drawer code
}
});
more.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Intent i = new Intent(ctx, stayrocks.jambh.vani.auth.MainActivity.class);
// ctx.startActivity(i);
if (mOnItemClickListener != null) {
mOnItemClickListener.openDrawer();
}
//open drawer code
}
});
bs.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent= new Intent(ctx, AmaActivity.class);
ctx.startActivity(intent);
}
});
bl.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(ctx, ItemListActivity.class);
ctx.startActivity(i);
//open drawer code
}
});
bng.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// String appPackage = "com.my.bishnoi.nextgen";
// Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://play.google.com/store/apps/details?id=" + appPackage));
// intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
Intent intent= new Intent(ctx, WallpaperActivity.class);
ctx.startActivity(intent);
//open drawer code
}
});
medi.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// String appPackage = "com.my.bishnoi.nextgen";
// Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://play.google.com/store/apps/details?id=" + appPackage));
// intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
Intent intent= new Intent(ctx, stayrocks.jambh.vani.activities.jyot.MainActivity.class);
ctx.startActivity(intent);
//open drawer code
}
});
vid.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// String appPackage = "com.my.bishnoi.nextgen";
// Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://play.google.com/store/apps/details?id=" + appPackage));
// intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
Intent intent= new Intent(ctx, VideoListDemoActivity.class);
ctx.startActivity(intent);
//open drawer code
}
});
// ama.setOnClickListener(new View.OnClickListener() {
// #Override
// public void onClick(View v) {
//// String appPackage = "com.my.bishnoi.nextgen";
//// Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://play.google.com/store/apps/details?id=" + appPackage));
//// intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
// Intent intent= new Intent(ctx, AmaActivity.class);
// ctx.startActivity(intent);
// //open drawer code
// }
// });
}
}
`

Add your imageView click listener in OnBindViewHolder method
#Override
public void onBindViewHolder(#NonNull final MyViewHolder holder, int position) {
holder.imageView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Do what you want here
}
});
}

How to have multiple intents on the same java program

public class FullscreenActivity extends AppCompatActivity {
private ImageButton act;
private ImageButton sat;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fullscreen);
act = (ImageButton) findViewById(R.id.act);
sat = (ImageButton) findViewById(R.id.sat);
sat.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick (View v) {
Intent intent = new Intent(FullscreenActivity.this, sat.class);
startActivity(intent);
act.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick (View v) {
Intent intent = new Intent(FullscreenActivity.this, act.class);
startActivity(intent);
}
});
}}
What am I doing worng. I have a main UI with six imagebuttons, each one linking to a different activity. How can I link then all in the main activity which is called fullscreen activity

I think you want to bring the FullScreenActivity to front so you only have to finish the front Activity because you didn't finish it
just do finish(); on your sat.class or act.class
or....
You can do this too on your sat.class or act.class:
Intent i = new Intent(this, FullScreenActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(i);

act.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick (View v) {
Intent intent = new Intent(FullscreenActivity.this, act.class);
startActivity(intent);
}
});
why is the above part inside some other button's click listener? Move it outside the anonymous inner method like
sat.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick (View v) {
Intent intent = new Intent(FullscreenActivity.this, sat.class);
startActivity(intent);
}
});
act.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick (View v) {
Intent intent = new Intent(FullscreenActivity.this, act.class);
startActivity(intent);
}
});

How to start needed Activity, when I saved data in file?

When app starts at first, start Activity with two button: Create File and Settings. Then if I click on button Create File - start Activity where I write text and save in file.
If we have error when file saved - start activity with two button. Else start another Activity with three buttons: Look file, Edit File, Settings.
How organize correct transitions between this Activity and How start activity with three buttons if file already saved?
public class MainFirstActivity extends AppCompatActivity {
private Button createFile;
private Button settings;
private boolean start = true;
private static final String MY_SETTINGS = "my_settings";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_first);
createFile = (Button) findViewById(R.id.create_file);
settings = (Button) findViewById(R.id.settings);
createFile.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainFirstActivity.this, CreateFileActivity.class);
startActivity(intent);
// MainFirstActivity.this.finish();
}
});
settings.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainFirstActivity.this, SettingActivity.class);
startActivity(intent);
}
});
}
#Override
protected void onResume() {
super.onResume();
File f = new File(CreateFileActivity.FILE_NAME);
if(!f.exists() && !f.isDirectory() && start) {
Intent intent = new Intent(MainFirstActivity.this, MainWithFileActivity.class);
startActivity(intent);
//start=false;
MainFirstActivity.this.finish();
Log.e("err", "intent");
}
}
}
MainWithFileActivity
public class MainWithFileActivity extends AppCompatActivity {
public static final String MY_SETTINGS = "MY_SETTINGS";
private Button lookFile;
private Button editFile;
private Button settings;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_if_first);
lookFile = (Button) findViewById(R.id.look_file);
settings = (Button) findViewById(R.id.settings);
editFile = (Button) findViewById(R.id.edit_file);
lookFile.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainWithFileActivity.this, LookFileActivity.class);
startActivity(intent);
}
});
editFile.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainWithFileActivity.this,CreateFileActivity.class);
startActivity(intent);
}
});
settings.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainWithFileActivity.this, SettingActivity.class);
startActivity(intent);
}
});
}
}

Simply check if the file exists. If it does not, hide the lookFile button
Add this in your MainWithFileActivity onCreate method
File f = new File(CreateFileActivity.FILE_NAME);
if(!f.exists() && !f.isDirectory()) {
lookFile.setVisibility(View.GONE);
}