'空對象引用'布爾android.os.Handler.postDelayed（java.lang.Runnable，long）'

Question

我在與主活動不同的類中創建了一個計時器。當我運行代碼時，出現以下錯誤：

java.lang.NullPointerException：試圖對null對象引用調用虛擬方法'boolean android.os.Handler.postDelayed（java.lang.Runnable，long）'

研究它是表明處理器沒有在我的代碼但是初始化它（如果我使用在mainActivity代碼線程，它工作正常）

誰能提供任何指針在何處，我要去錯了嗎？

主要活動：

public class MainActivity extends AppCompatActivity { 

private ListView listView; 
TextView timertxt; //this 
public static TextView hourtext;//this2 
int time; //this 




@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    timertxt = (TextView) findViewById(R.id.timertxt);//this 
    hourtext = (TextView) findViewById(R.id.SessionTimerTxt);//this 2 
    final Timer timer; 



    final Button generate = (Button) findViewById(R.id.Generate); 
    generate.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      DatabaseAccess myDatabaseHelper = new DatabaseAccess(MainActivity.this); 
      myDatabaseHelper.open(); 
      Cursor d = myDatabaseHelper.getRProgram(); 
      if (d.moveToFirst()) ; 
      DisplayProgram(d); 

      myDatabaseHelper.close(); 

      Timer timer = new Timer(); 
      timer.count(); 
      //the abpove two lines r causing it to crash prob cos timer class is trying to change text on UI 


     } 

     public void DisplayProgram(Cursor d) { 
      TextView result2 = (TextView) findViewById(R.id.result2); 
      result2.setText("\n" + d.getString(1)+ " " + (d.getLong(2)*1000)); 
      time = (d.getInt(2)*1000); 


      TextView dbtime = (TextView) findViewById(R.id.dbtimeproof); 
      dbtime.setText (String.valueOf (time)); 

      final MyCount counter = new MyCount(time,1000);//this 
      counter.start(); 

      Button TButton = (Button) findViewById(R.id.tbutton); 
      TButton.setOnClickListener(new View.OnClickListener() { 
       @Override 
       public void onClick(View view) { 

        //counter.start(); 

       } 
      }); 

     } 

    }); 

} 


// count down timer is an abstract class, so extend it and fill in methods 
public class MyCount extends CountDownTimer { //all below here 

    public MyCount(long millisInFuture, long countDownInterval) { 
     super(millisInFuture, countDownInterval); 
    } 

    @Override 
    public void onFinish() { 
     // it's done 
     timertxt.setText("Done!"); 


    } 

    @Override 
    public void onTick(long millisUntilFinished) { 
     timertxt.setText("Left: " + millisUntilFinished/1000); 

     final String ifvaluest = timertxt.getText().toString(); 

     //if hour timer is greater than 1 sec then process below else skip below 

     if (ifvaluest.equals("Left: 1")){ 


      DatabaseAccess myDatabaseHelper = new DatabaseAccess(MainActivity.this); 
      myDatabaseHelper.open(); 
      Cursor d = myDatabaseHelper.getRProgram(); 
      if (d.moveToFirst()) ; 
      DisplayProgram(d); 

      myDatabaseHelper.close();}} 

     public void DisplayProgram(Cursor d) { 
      TextView result2 = (TextView) findViewById(R.id.result2); 
      result2.setText("\n" + d.getString(1)+ " " + (d.getLong(2)*1000)); 
      time = (d.getInt(2)*1000); 


      TextView dbtime = (TextView) findViewById(R.id.dbtimeproof); 
      dbtime.setText (String.valueOf (time)); 

      final MyCount counter = new MyCount(time,1000);//this 
      counter.start(); 



     } 
    } 


} 

繼承人的Timer類：

public class Timer extends AppCompatActivity { 

//TextView hourtext; 
private int elapsedTime;// used to hold elapsed time 
public Handler handler; 
private int interval = 60000;//millisecs count 





@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    //hourtext = (TextView) findViewById(R.id.SessionTimerTxt); 
    elapsedTime = 0; 
    handler = new Handler();//initialise the handler 
    count(); 



}//starts the count 


    public void count() { 
     runOnUiThread(new Runnable() { 
      @Override 
      public void run() { 


     elapsedTime++; //increase the counter 
     MainActivity.hourtext.setText(String.valueOf(elapsedTime)); 
     handler.postDelayed(runnable, interval); // call the runnable 
      } 
     }); 


}//ends of the count section 

// Runnable - calls the count() function to continue the sequence 
private Runnable runnable = new Runnable() { 
    @Override 
    public void run() { 
     count(); 
    } 
}; //end runnable section 



} //end of class 

Answer 1

只是靈機一動！因爲我沒有在runonui中實例化處理程序。所以爲了讓它工作，我剛剛添加了以下代碼ABOVE elapsedtime ++

handler = new Handler（）;

Answer 2

你不需要AppCompatActivity

public class Timer { 
//TextView hourtext; 
private int elapsedTime; // used to hold elapsed time 
public Handler handler; 
private int interval = 60000; //millisecs count 
private Context ctx; 
Timer(context contxt) { 
    ctx = contxt; 
} 

public void count() { 
    elapsedTime = 0; 
    handler = new Handler(); //initialise the handler 
    count(); 

    ((Activity) ctx).runOnUiThread(new Runnable() { 
    @Override 
    public void run() { 


    elapsedTime++; //increase the counter 
    MainActivity.hourtext.setText(String.valueOf(elapsedTime)); 
    handler.postDelayed(runnable, interval); // call the runnable 
    } 
    }); 


    } //ends of the count section 

// Runnable - calls the count() function to continue the sequence 
private Runnable runnable = new Runnable() { 
    @Override 
    public void run() { 
    count(); 
    } 
}; //end runnable section 



} //end of class 

你MainActivity.java延伸

public class MainActivity extends AppCompatActivity { 

private ListView listView; 
TextView timertxt; //this 
public static TextView hourtext; //this2 
int time; //this 




@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    timertxt = (TextView) findViewById(R.id.timertxt); //this 
    hourtext = (TextView) findViewById(R.id.SessionTimerTxt); //this 2 
    final Timer timer; 



    final Button generate = (Button) findViewById(R.id.Generate); 
    generate.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View view) { 
    DatabaseAccess myDatabaseHelper = new DatabaseAccess(MainActivity.this); 
    myDatabaseHelper.open(); 
    Cursor d = myDatabaseHelper.getRProgram(); 
    if (d.moveToFirst()); 
    DisplayProgram(d); 

    myDatabaseHelper.close(); 

    Timer timer = new Timer(MainActivity.this); 
    timer.count(); 
    //the above two lines r causing it to crash prob cos timer class is trying to change text on UI 


    } 

    public void DisplayProgram(Cursor d) { 
    TextView result2 = (TextView) findViewById(R.id.result2); 
    result2.setText("\n" + d.getString(1) + " " + (d.getLong(2) * 1000)); 
    time = (d.getInt(2) * 1000); 


    TextView dbtime = (TextView) findViewById(R.id.dbtimeproof); 
    dbtime.setText(String.valueOf(time)); 

    final MyCount counter = new MyCount(time, 1000); //this 
    counter.start(); 

    Button TButton = (Button) findViewById(R.id.tbutton); 
    TButton.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View view) { 

     //counter.start(); 

    } 
    }); 

    } 

    }); 

} 


// count down timer is an abstract class, so extend it and fill in methods 
public class MyCount extends CountDownTimer { //all below here 

    public MyCount(long millisInFuture, long countDownInterval) { 
    super(millisInFuture, countDownInterval); 
    } 

    @Override 
    public void onFinish() { 
    // it's done 
    timertxt.setText("Done!"); 


    } 

    @Override 
    public void onTick(long millisUntilFinished) { 
    timertxt.setText("Left: " + millisUntilFinished/1000); 

    final String ifvaluest = timertxt.getText().toString(); 

    //if hour timer is greater than 1 sec then process below else skip below 

    if (ifvaluest.equals("Left: 1")) { 


    DatabaseAccess myDatabaseHelper = new DatabaseAccess(MainActivity.this); 
    myDatabaseHelper.open(); 
    Cursor d = myDatabaseHelper.getRProgram(); 
    if (d.moveToFirst()); 
    DisplayProgram(d); 

    myDatabaseHelper.close(); 
    } 
    } 

    public void DisplayProgram(Cursor d) { 
    TextView result2 = (TextView) findViewById(R.id.result2); 
    result2.setText("\n" + d.getString(1) + " " + (d.getLong(2) * 1000)); 
    time = (d.getInt(2) * 1000); 


    TextView dbtime = (TextView) findViewById(R.id.dbtimeproof); 
    dbtime.setText(String.valueOf(time)); 

    final MyCount counter = new MyCount(time, 1000); //this 
    counter.start(); 



    } 
} 


}