Введенное имя пользователя не появится после названия приложения

Question

Я разрабатываю приложение простого списка дел, где на странице приветствия вы вводите свое имя и когда вы нажимаете, чтобы перейти к своим задачам (на странице задач), ваше имя пользователя, которое вы только что введенное должно появиться в верхней части экрана (например: «Приложение: Имя пользователя»), но когда я попробовал это, он появился как «Приложение: null» на странице приветствия и «null: null» на странице задач. Может ли кто-нибудь понять, почему? Спасибо.

Welcome.java

package winfield.joe.assignment.two; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.RatingBar; 
import android.widget.RatingBar.OnRatingBarChangeListener; 
import android.widget.Toast; 
import android.widget.ToggleButton; 
import android.app.ProgressDialog; 
import android.widget.CheckBox; 

public class Welcome extends Activity { 

    //global vars 
    private CheckBox check; 
    private ProgressDialog progress; 
    private ToggleButton toggleButton; 
    private RatingBar ratingBar; 

    private String givenTitle; 
    private String username; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 

     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_welcome); 

     givenTitle = (String) this.getTitle(); 

     progress = new ProgressDialog(this); 

     addListenerOnCheck(); 
     addListenerOnButton(); 
     addListenerOnRatingBar(); 

    } 

    //on click CheckBox displays a toast message - CLICK! 
    public void addListenerOnCheck() { 

     check = (CheckBox) findViewById(R.id.check); 
     check.setOnClickListener(new OnClickListener() { 

      public void onClick(View v) { 
       StringBuffer result = new StringBuffer(); 
       result.append("CLICK!"); 
       Toast.makeText(Welcome.this, result.toString(), Toast.LENGTH_SHORT).show(); 
      } 

     }); 

    } 

    //on click toggle button displays on/off 
    public void addListenerOnButton() { 

     toggleButton = (ToggleButton) findViewById(R.id.toggleButton); 
     toggleButton.setOnClickListener(new OnClickListener() { 

      public void onClick(View v) { 
       StringBuffer result = new StringBuffer(); 
       result.append("Toggle = ").append(toggleButton.getText());   
       Toast.makeText(Welcome.this, result.toString(), Toast.LENGTH_SHORT).show(); 
      } 

     }); 

    } 

    //Give a rating - Toast appears of star rating 
    public void addListenerOnRatingBar() { 

     ratingBar = (RatingBar) findViewById(R.id.ratingBar); 
     //if rating value has changed, display the current rating on a toast 
     ratingBar.setOnRatingBarChangeListener(new OnRatingBarChangeListener() { 

      public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) { 
       Toast.makeText(Welcome.this, String.valueOf(ratingBar.getRating()), Toast.LENGTH_SHORT).show(); 
      } 

     }); 

    } 

    //Onclick - go to About 
    public void aboutMe(View view) { 

     Intent intent = new Intent(Welcome.this, About.class); 

     startActivity(intent); 

    } 

    //Onclick - go to Tasks 
    public void doStuff(View view) { 

     this.setTitle(givenTitle + ": " + username); 

     Intent intent = new Intent(Welcome.this, Tasks.class); 
     startActivity(intent); 

     //ProgressBarDialog appears saying its finding yours tasks and loads to 100 and changes activity 
     progress.setMessage("Finding tasks..."); 
     progress.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); 
     progress.setIndeterminate(true); 
     progress.show(); 

     //Goes to 100 
     final int totalProgressTime = 100; 

     final Thread t = new Thread(){ 

      @Override 
      public void run(){ 

       //Goes from 0 to 100 in jumps of 5 until the total amount of jumps reaches 100/total progress time 
       int jumpTime = 0; 
       while(jumpTime < totalProgressTime){ 
       try { 
        Thread.sleep(200); 
        jumpTime += 5; 
        progress.setProgress(jumpTime); 
       } catch (InterruptedException e) { 
        // TODO Auto-generated catch block 
        e.printStackTrace(); 
       } 
       } 

      } 

     }; t.start(); 

    } 

} 

Tasks.java

package winfield.joe.assignment.two; 

import android.app.AlertDialog; 
import android.app.ListActivity; 
import android.content.ContentValues; 
import android.content.DialogInterface; 
import android.content.Intent; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.*; 
import winfield.joe.assignment.two.database.TaskContract; 
import winfield.joe.assignment.two.database.TaskDBHelper; 

public class Tasks extends ListActivity { 

    //add required global variables 
    private ListAdapter listAdapter; 
    private TaskDBHelper helper; 

    private String givenTitle; 
    private String username; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_tasks); 
     updateUI(); 

     this.setTitle(givenTitle + ": " + username); 

    } 

    //add in the menu (refers to menu.xml file) 
    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     getMenuInflater().inflate(R.menu.menu,menu); 
     return true; 
    } 

    //to get selected tasks from menu 
    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     switch (item.getItemId()) { 
      case R.id.action_add_task: 
       //create new alert dialog which asks you if you want to make a new task entry 
       AlertDialog.Builder builder = new AlertDialog.Builder(this); 
       builder.setTitle("Add a new task"); 
       builder.setMessage("What do you need to do?"); 
       final EditText inputField = new EditText(this); 
       builder.setView(inputField); 
       //if 'add' then place it into the db, update it 
       builder.setPositiveButton("Add", new DialogInterface.OnClickListener() { 

        @Override 
        public void onClick(DialogInterface dialogInterface, int i) { 
         //Clicking add - stores data in the database 
         String task = inputField.getText().toString(); 
         helper = new TaskDBHelper(Tasks.this); 
         SQLiteDatabase db = helper.getWritableDatabase(); 
         ContentValues values = new ContentValues(); 
         values.clear(); 
         values.put(TaskContract.Columns.TASK,task); 
         db.insertWithOnConflict(TaskContract.TABLE,null,values,SQLiteDatabase.CONFLICT_IGNORE); 
         updateUI(); 
        } 
       }); 

       //quits out of alert dialog and goes back to the task list if 'cancel' 
       builder.setNegativeButton("Cancel",null); 

       builder.create().show(); 
       return true; 

      default: 
       return false; 
     } 
    } 

    //Show database entries on the tasks page 
    private void updateUI() { 
     helper = new TaskDBHelper(Tasks.this); 
     SQLiteDatabase sqlDB = helper.getReadableDatabase(); 
     Cursor cursor = sqlDB.query(TaskContract.TABLE, new String[]{ 
       TaskContract.Columns._ID, TaskContract.Columns.TASK 
     }, 
       null, null, null, null, null); 
     listAdapter = new SimpleCursorAdapter(
       this, 
       R.layout.task_view, 
       cursor, 
       new String[]{TaskContract.Columns.TASK}, 
       new int[]{R.id.taskTextView}, 
       0 
     ); 
     this.setListAdapter(listAdapter); 
    } 

    //Deletes tasks (clicking done next to them) 
    public void onDoneButtonClick(View view) { 
     View v = (View) view.getParent(); 
     TextView taskTextView = (TextView) v.findViewById(R.id.taskTextView); 
     String task = taskTextView.getText().toString(); 
     //This query deletes the entry associated with the id/button pressed 
     String sql = String.format("DELETE FROM %s WHERE %s = '%s'", 
         TaskContract.TABLE, 
         TaskContract.Columns.TASK, 
         task); 

     helper = new TaskDBHelper(Tasks.this); 
     SQLiteDatabase sqlDB = helper.getWritableDatabase(); 
     sqlDB.execSQL(sql); 
     updateUI(); 
    } 

    //onClick finished method assigned to the 'Finished' button 
    public void finished(View view) { 

      //Make alert dialog box appear and give it it's title 
      AlertDialog.Builder builder = new AlertDialog.Builder(this); 
      builder.setTitle(getString(R.string.alert)); 

       // set dialog message 
       builder.setCancelable(false) 

         //Positive response = return to list (tasks page) 
         .setPositiveButton(getString(R.string.positive),new DialogInterface.OnClickListener() { 
          public void onClick(DialogInterface dialog,int id) { 
           //You return to the Tasks 
           dialog.cancel(); 
          } 
         }) 

         //Neutral response = go to about (about page) 
         .setNeutralButton(getString(R.string.neutral),new DialogInterface.OnClickListener() { 
          public void onClick(DialogInterface dialog,int id) { 
           //You go to About Activity 
           Intent intent = new Intent(Tasks.this, About.class); 
           startActivity(intent); 
          } 
         }) 

         //Negative response = exit app (homescreen) 
         .setNegativeButton(getString(R.string.negative),new DialogInterface.OnClickListener() { 
          public void onClick(DialogInterface dialog,int id) { 
           // if this button is clicked, exit app to homescreen 
           Intent intent = new Intent(Intent.ACTION_MAIN); 
           intent.addCategory(Intent.CATEGORY_HOME); 
           startActivity(intent); 
          } 
         }); 

      //create it and show it 
      AlertDialog alert = builder.create(); 
      alert.show(); 

     } 

} 

Имя пользователя в пределах activity_welcome.xml

<EditText 
    android:ems="10" 
    android:hint="@+string/username" 
    android:id="@+id/username" 
    android:inputType="text" 
    android:layout_height="wrap_content" 
    android:layout_marginEnd="30dp" 
    android:layout_marginStart="30dp" 
    android:layout_marginTop="30dp" 
    android:layout_width="match_parent"> 

    <requestFocus/> 
</EditText> 

Соответствующие строки из strings.xml

<string name="app_name">ForYouToDo</string> 
<string name="username">Username</string> 

Answer 1

Перейти к Android - Pass Data Between Two Activities get NullPointerException

Полное руководство (How to pass data between two activity?)

и сделать в вашем Tasks Activity

this.setTitle(getResources().getString(R.string.app_name)+ ": " + username);