如何在android中處理NullPointerException？

01-18 02:08:05.271: E/AndroidRuntime(24688): FATAL EXCEPTION: main 
01-18 02:08:05.271: E/AndroidRuntime(24688): java.lang.NullPointerException 
01-18 02:08:05.271: E/AndroidRuntime(24688): at com.example.tava.EchangingMessage$LoadData.onPostExecute(EchangingMessage.java:178) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at com.example.tava.EchangingMessage$LoadData.onPostExecute(EchangingMessage.java:1) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at android.os.AsyncTask.finish(AsyncTask.java:602) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at android.os.AsyncTask.access$600(AsyncTask.java:156) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:615) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at android.os.Handler.dispatchMessage(Handler.java:99) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at android.os.Looper.loop(Looper.java:154) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at android.app.ActivityThread.main(ActivityThread.java:4945) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at java.lang.reflect.Method.invokeNative(Native Method) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at java.lang.reflect.Method.invoke(Method.java:511) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
01-18 02:08:05.271: E/AndroidRuntime(24688): at dalvik.system.NativeStart.main(Native Method)

這是我的代碼活動代碼：如何在android中處理NullPointerException？

public class EchangingMessage extends Activity implements OnClickListener { 

    private ProgressDialog pDialog; 
    JSONParser jParser = new JSONParser(); 
    ArrayList<HashMap<String, String>> DaftarRS; 
    EditText textToSend; 

    ArrayList<HashMap<String, String>> arraylist; 

    private static String url_daftar_rs = "http://192.168.137.1/www/Android_Login_Secure/detailMessage.php"; 
    private static String url_daftar_rs1 = "http://192.168.137.1/www/Android_Login_Secure/myFriends.php"; 

    public static final String TAG_SUCCESS = "success"; 
    public static final String TAG_DAFTAR_RS = "daftar_rs"; 
    public static final String TAG_ID_RS = "id_rs"; 
    public static final String TAG_NAMA_RS = "username"; 
    public static final String TAG_LINK_IMAGE_RS = "image"; 
    public static final String TAG_MESSAGE_RS = "messageText"; 
    public static final String TAG_TIME_RS = "sendAt"; 
    public static final String TAG_SEEN_RS = "readStatus"; 

    JSONArray daftar_rs = null; 

    ListAdapterUserOnile adapterFirends; 

    ImageView showOnline; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.exchange_message); 
arraylist = new ArrayList<HashMap<String, String>>(); 
    } 

    @Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 

     switch (v.getId()) { 

     case R.id.userOnline: 
      userOnlineWindow(); 
      break; 

     } 

    } 

    private void userOnlineWindow() { 
     // TODO Auto-generated method stub 

     LayoutInflater layoutInflater = (LayoutInflater) getBaseContext() 
       .getSystemService(LAYOUT_INFLATER_SERVICE); 
     View popupView = layoutInflater.inflate(R.layout.popup, null); 
     final PopupWindow popupWindow = new PopupWindow(popupView, 
       LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); 

     Button btnDismiss = (Button) popupView.findViewById(R.id.dismiss); 
     btnDismiss.setOnClickListener(new Button.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       popupWindow.dismiss(); 
      } 
     }); 

     popupWindow.showAsDropDown(showOnline, -190, -90); 

     new LoadData().execute(); 

     popupWindow.setFocusable(true); 
     popupWindow.update(); 
    } 

    class LoadData extends AsyncTask<String, String, String> { 

     @Override 
     protected void onPreExecute() { 
      super.onPreExecute(); 
      pDialog = new ProgressDialog(EchangingMessage.this); 
      pDialog.setMessage("Loading Information..."); 
      pDialog.setIndeterminate(false); 
      pDialog.setCancelable(false); 
      pDialog.show(); 
     } 

     @Override 
     protected String doInBackground(String... arg0) { 

      List<NameValuePair> params1 = new ArrayList<NameValuePair>(); 

      params1.add(new BasicNameValuePair("me", "52")); 

      JSONObject json = jParser.makeHttpRequest(url_daftar_rs1, "POST", 
        params1); 

      try { 

       int success = json.getInt(TAG_SUCCESS); 
       Log.i("success :", "" + success); 

       if (success == 1) { 

        daftar_rs = json.getJSONArray(TAG_DAFTAR_RS); 
        for (int i = 0; i < daftar_rs.length(); i++) { 
         JSONObject c = daftar_rs.getJSONObject(i); 
         String id_rs = c.getString(TAG_ID_RS); 
         String nama_rs = c.getString(TAG_NAMA_RS); 
         String link_image_rs = c.getString(TAG_LINK_IMAGE_RS); 

         HashMap<String, String> map = new HashMap<String, String>(); 

         map.put(TAG_ID_RS, id_rs); 
         map.put(TAG_NAMA_RS, nama_rs); 
         map.put(TAG_LINK_IMAGE_RS, 
           "http://192.168.137.1/www/Android_Login_Secure/Images/upload/big/" 
             + link_image_rs); 

         arraylist.add(map); 

        } 
       } else { 

       } 
      } catch (Exception e) { 
       Log.e("Error", "COnnection:" + e.toString()); 
      } 
      return null; 
     } 

     protected void onPostExecute(String file_url) { 
      pDialog.dismiss(); 



     ListView listUserOnline = (ListView) findViewById(R.id.listOfUserOnline); 


      adapterFirends = new ListAdapterUserOnile(EchangingMessage.this, 
        arraylist); 

      listUserOnline.setAdapter(adapterFirends); 

     } 
    } 

}

我創造了這個應用程序，但是當我點擊頂部按鈕我得到這個錯誤，這是彈出窗口，這是連接用PHP

請如何處理這個錯誤我該怎麼辦？

enter image description here

，這我EchangeMesssage.xml文件

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:background="@drawable/backgroudnformain" 
    android:orientation="vertical" > 
    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="40dp" 
     android:background="#99cc00" 
     android:gravity="center" 
     > 

     <ImageView 
      android:id="@+id/userOnline" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_gravity="center" 
      android:src="@drawable/userimages" /> 

    </LinearLayout> 

    <LinearLayout 
     android:id="@+id/bottom_write_bar" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_alignParentBottom="true" 
     android:background="@drawable/message_bar" > 

     <EditText 
      android:id="@+id/messageToSend" 
      android:layout_width="fill_parent" 
      android:layout_height="fill_parent" 
      android:layout_margin="5sp" 
      android:layout_weight="1" 
      android:background="@drawable/message_field" 
      android:hint="Write here" 
      android:padding="5sp" 
      android:textColor="@color/textFieldColor" /> 

     <Button 
      android:id="@+id/sendButton" 
      android:layout_width="wrap_content" 
      android:layout_height="fill_parent" 
      android:layout_margin="5sp" 
      android:background="@drawable/send_button" 
      android:onClick="sendMessage" 
      android:paddingBottom="5sp" 
      android:paddingLeft="15sp" 
      android:paddingRight="15sp" 
      android:paddingTop="5sp" 
      android:text="Send" 
      android:textColor="#FFF" /> 

    </LinearLayout> 

    <ListView 
     android:id="@+id/listSend" 
     android:layout_width="fill_parent" 
     android:layout_height="0dip" 
     android:layout_marginTop="40dp" 
     android:layout_above="@id/bottom_write_bar" 
     android:layout_alignParentTop="true" 
     android:cacheColorHint="#00000000" 
     android:divider="#00000000" 
     android:stackFromBottom="true" 
     android:clickable="false" 
     android:scrollbars="none" 
     android:transcriptMode="alwaysScroll" 
     android:listSelector="#00000000" > 
    </ListView> 


     <TextView 
      android:id="@+id/you_id" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="Large Text" 
      android:textAppearance="?android:attr/textAppearanceLarge" 
      android:visibility="gone" /> 

     <TextView 
      android:id="@+id/me_id" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="Large Text" 
      android:textAppearance="?android:attr/textAppearanceLarge" 
      android:visibility="gone" /> 


</RelativeLayout>

，這是我popup.xml文件：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:background="@drawable/windowwww" 
    android:orientation="vertical" > 

    <Button 
     android:id="@+id/dismiss" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_marginLeft="240dp" 
     android:layout_marginTop="60dp" 
     android:text="EXIT" /> 

    <ListView 
     android:id="@+id/listOfUserOnline" 
     android:layout_width="match_parent" 
     android:layout_height="330dp" 
     android:layout_marginTop="30dp" > 
    </ListView> 

</LinearLayout>

這是我ListAdapter類：

public class ListAdapterUserOnile extends BaseAdapter { 

    public String POST_TEXT; 
    private Activity activity; 
    private ArrayList<HashMap<String, String>> data; 
    private static LayoutInflater inflater = null; 
    public ImageLoader imageLoader; 
    public final static String you_id=null; 

    int count = 0; 

    public ListAdapterUserOnile(Activity a, ArrayList<HashMap<String, String>> d) { 
     activity = a; 
     data = d; 
     inflater = (LayoutInflater) activity 
       .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     imageLoader = new ImageLoader(activity.getApplicationContext()); 
    } 

    public int getCount() { 
     // TODO Auto-generated method stub 
     return data.size(); 
    } 

    public Object getItem(int position) { 
     return position; 
    } 

    public long getItemId(int position) { 
     return position; 
    } 

    public View getView(int position, View convertView, ViewGroup parent) { 
     View vi = convertView; 
     if (convertView == null) { 
      vi = inflater.inflate(R.layout.item_list_friends, null); 
     } 

     TextView name_rs = (TextView) vi.findViewById(R.id.myFriendUsername); 


     ImageView thumb_image = (ImageView) vi 
       .findViewById(R.id.myFriendImage); 


     TextView status = (TextView) vi.findViewById(R.id.status); 

     ImageView on=(ImageView) vi.findViewById(R.id.online); 
     ImageView off=(ImageView) vi.findViewById(R.id.offline); 

     HashMap<String, String> daftar_rs = new HashMap<String, String>(); 
     daftar_rs = data.get(position); 
     final int getPosition = position; 
     name_rs.setText(daftar_rs.get(EchangingMessage.TAG_NAMA_RS)); 







     Log.e("IMage", daftar_rs.get(EchangingMessage.TAG_LINK_IMAGE_RS)); 

     imageLoader.DisplayImage(daftar_rs.get(EchangingMessage.TAG_LINK_IMAGE_RS), 
       thumb_image); 

     if (status.getText().toString().equals("1")) { 

      off.setVisibility(View.INVISIBLE); 
      on.setVisibility(View.VISIBLE); 
      status.setVisibility(View.INVISIBLE); 

     } 
     else 
     { 
      off.setVisibility(View.VISIBLE); 
      on.setVisibility(View.INVISIBLE); 
      status.setVisibility(View.INVISIBLE); 
     } 




     vi.setOnClickListener(new OnClickListener() { 



      @Override 
      public void onClick(View arg0) { 
       // TODO Auto-generated method stub 
       Toast.makeText(
         activity, 
         " You click" 
           + data.get(getPosition) 
             .get(MyFriends.TAG_ID_RS).toString(), 
         Toast.LENGTH_SHORT).show(); 

       Intent i=new Intent(activity,EchangingMessage.class); 
       i.putExtra(you_id, data.get(getPosition) 
             .get(MyFriends.TAG_ID_RS).toString()); 
       activity.startActivity(i); 


      } 
     }); 

     return vi; 

    } 

}

來源

2014-01-17 Shanaz K

哪條線對應的行號178？ – nKn

你確定變量listUserOnline不是null嗎？如果您的ID在R.java中找不到給定的ID，findViewByID可以返回null。 – Prmths

yess你是對的我刪除了一些代碼現在看這個 –

當您使用setContentView(R.layout.exchange_message)，佈局R.layout.exchange_message會膨脹，並關聯到你的活動。如果您想從該佈局中檢索視圖，則只需撥打findViewById(R.id.MyId);即可。

但是，如果您的視圖不在佈局中，您將有一個NPException。

要從其他佈局檢索視圖，必須首先對其進行充氣，然後致電myView.findViewById(R.id.MyId)。

舉例來說，根據你的情況，如果你想從popup.xml佈局文件使用ListView：

View popupView = layoutInflater.inflate(R.layout.popup, null); 
    ListView list = popupView.findViewById(R.id.listOfUserOnline);

來源

2014-01-17 23:28:52

對不起你什麼意思？ –

看到我的編輯，希望現在清楚。 –

ohhhhhhhhhhhhhh真的很reallllllllllllllllllllly謝謝這是3天 ohhhhhhhhhhh終於感謝youuuuuuuuuuuuuuuuuuuuuuuuuuuuuu洙多 –

你需要學習閱讀日誌來解決像NPE那樣的錯誤。顯示java.lang.NullPointerException在com.example.tava.EchangingMessage $ LoadData.onPostExecute * （EchangingMessage.java:178） *

你的錯誤是最有可能在此行。要顯示在eclipse中的行號，請右鍵單擊左邊的邊緣，然後選擇「顯示行號」另外，鍵盤命令Ctrl + L將讓您跳轉到特定行。

調用findViewById代替您的popupWindow。將變量提取到類級別或將其傳遞給AsyncTask，以便可以引用它。

popupWindow.findViewById();

來源

2014-01-17 23:19:35

listUserOnline.setAdapter（adapterFirends）;？！這是我的錯誤點 –

你給他/她一個很好的建議，但你沒有太多幫助他/她，他/她給出了行號和代碼，NPE的原因是什麼？對此的回答可以幫助他/她更好...... –

然後你的findViewById（R .id.listOfUserOnline）失敗，你確定這個id是正確的嗎？它是否具有該視圖的活動？如果該視圖屬於另一個組件，則必須調用.findViewById。例如，如果它屬於一個對話框需要在對話框中調用它，從而使其dialog.findViewById（） –

如何在android中處理NullPointerException？

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