顯示當前時間

Question

我目前正試圖顯示當前時間到我的自定義ListView，但我不斷收到一個NullPointerException，並想知道我做錯了什麼，因爲我已經添加到數組並獲取它的值。

定製適配器和setter/getter方法在這裏：12

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    listView = (ListView) findViewById(R.id.list_view); 
    boss_title = getResources().getStringArray(R.array.boss_array); 
    bossTime = (TextView) findViewById(R.id.boss_time); 

    adapter = new BossAdapter(getApplicationContext(), R.layout.boss_layout); 
    listView.setAdapter(adapter); 
    int i = 0; 


    Thread t = new Thread() { 

     @Override 
     public void run() { 
      try { 
       while (!isInterrupted()) { 
        Thread.sleep(1000); 
        runOnUiThread(new Runnable() { 
         @Override 
         public void run() { 
          Calendar c = Calendar.getInstance(); 
          SimpleDateFormat df = new SimpleDateFormat("HH-mm-ss"); 
          String formattedTime = df.format(c.getTime()); 

          String [] boss_time_array = new String[6]; 
          for(int i =0; i < 6; i++){ 
           boss_time_array[i] = formattedTime; 
          } 

          boss_time = boss_time_array; 

         } 
        }); 
       } 
      } catch (InterruptedException e) { 
      } 
     } 
    }; 

    t.start(); 

    for (String boss : boss_title) { 
     Boss bossObject = new Boss(boss_icon[i], boss, boss_time[i]); 

     adapter.add(bossObject); 
     i++; 
    } 

} 

logcat的

8541-8541/baegmon.com.bosstimer E/AndroidRuntime﹕ FATAL EXCEPTION: main 
Process: baegmon.com.bosstimer, PID: 8541 
java.lang.RuntimeException: Unable to start activity ComponentInfo{baegmon.com.bosstimer/baegmon.com.bosstimer.MainActivity}:  java.lang.NullPointerException: Attempt to read from null array 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
     at android.app.ActivityThread.access$800(ActivityThread.java:151) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:135) 
     at android.app.ActivityThread.main(ActivityThread.java:5257) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
Caused by: java.lang.NullPointerException: Attempt to read from null array 
     at baegmon.com.bosstimer.MainActivity.onCreate(MainActivity.java:67) 
     at android.app.Activity.performCreate(Activity.java:5990) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
     at android.app.ActivityThread.access$800(ActivityThread.java:151) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:135) 
     at android.app.ActivityThread.main(ActivityThread.java:5257) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 

如何修改，以便它不返回空指針錯誤，並返回我的列表視圖的正確時間？

Answer 1

Handler handler=new Handler(); 
handler.post(new Runnable(){ 

     @Override 
     public void run() { 

      // upadte textView here 

      handler.postDelayed(this,500); // set time here to refresh textView 

     } 

    }); 

只是通過你的TextView在hanlder方法。這工作正常。

Answer 2

嘗試從下面的網站實現此代碼。

Calendar c = Calendar.getInstance(); 
SimpleDateFormat sdf = new SimpleDateFormat("dd:MMMM:yyyy HH:mm:ss a"); 
String strDate = sdf.format(c.getTime()); 

希望有任何疑問或疑問，請告訴我。

Answer 3

由於在創建適配器時線程未完成，您將收到NullPointerException。 線程啓動後，您立即讀取boss_title的結果。 這是不可能的，因爲你必須等待它完成。

您應該爲此使用AsyncTask並在onPostExecute（http://developer.android.com/reference/android/os/AsyncTask.html）中創建適配器。

而且SimpleDateFormat的類不是線程安全的：

public static Date dateToString(Date date, final String format, final Locale locale) 
    ThreadLocal<SimpleDateFormat> formater = new ThreadLocal<SimpleDateFormat>() { 
    @Override 
    protected SimpleDateFormat initialValue() { 
     return new SimpleDateFormat(format, locale); 
    } 
    }; 
    return formater.get().format(string); 
}