android - 无法恢复 Activity

Question

我是新手，我试图让我的 ListView 在我的 SQLite 数据库更新后刷新。修改我的 onResume() 方法后，我没有收到编译错误。我正在使用 SimpleCursorAdapter 重新查询，但它不起作用。收到的错误来自 logcat，如下所示。请指教……示例最有帮助。

日志:

  02-19 21:31:49.933: E/AndroidRuntime(714): java.lang.RuntimeException: Unable to resume activity {com.loginplus.home/com.loginplus.home.LoginList}: java.lang.NullPointerException
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2444)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2472)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1986)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.ActivityThread.access$600(ActivityThread.java:123)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.os.Handler.dispatchMessage(Handler.java:99)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.os.Looper.loop(Looper.java:137)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.ActivityThread.main(ActivityThread.java:4424)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at java.lang.reflect.Method.invokeNative(Native Method)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at java.lang.reflect.Method.invoke(Method.java:511)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at dalvik.system.NativeStart.main(Native Method)
  02-19 21:31:49.933: E/AndroidRuntime(714): Caused by: java.lang.NullPointerException
  02-19 21:31:49.933: E/AndroidRuntime(714):    at com.loginplus.home.LoginList.onResume(LoginList.java:101)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1154)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.Activity.performResume(Activity.java:4539)
  02-19 21:31:49.933: E/AndroidRuntime(714):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2434)

Activity :

     public class LoginList extends Activity implements OnClickListener,    OnItemClickListener {

private ListView loginList;
private Button webLogin;

private ListAdapter loginListAdapter;

private ArrayList<LoginDetails> loginArrayList;

List<String> arrayList = new ArrayList<String>();

@Override 
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    arrayList = populateList();
    loginListAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, populateList());
    setContentView(R.layout.login_listview);


    loginList = (ListView)
   findViewById(R.id.loginlist);
    loginList.setOnItemClickListener(this);

    webLogin = (Button)
   findViewById(R.id.button3);
    webLogin.setOnClickListener(this);


}

@Override
public void onClick (View v) {
    Intent webLoginIntent = new Intent (this, LoginPlusActivity.class);
    startActivity(webLoginIntent);

}

public List<String> populateList (){

    List<String> webNameList = new ArrayList<String>();

    dataStore openHelperClass = new dataStore (this);

    SQLiteDatabase sqliteDatabase = openHelperClass.getReadableDatabase();

    Cursor cursor = sqliteDatabase.query(dataStore.TABLE_NAME_INFOTABLE, null, null, null, null, null, dataStore.COLUMN_NAME_SITE, null);

    startManagingCursor(cursor);


    while (cursor.moveToNext()){
    String sName = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_SITE));
    String wUrl = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_ADDRESS));
    String uName = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_USERNAME));
    String pWord = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_PASSWORD));
    String lNotes = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_NOTES));

    LoginDetails lpDetails = new LoginDetails();

        lpDetails.setsName(sName);
        lpDetails.setwUrl(wUrl);
        lpDetails.setuName(uName);
        lpDetails.setpWord(pWord);
        lpDetails.setlNotes(lNotes);

        loginArrayList.add(lpDetails);
        webNameList.add(sName);
}

sqliteDatabase.close();
return webNameList;
}



@Override
protected void onResume() {
    super.onResume();

    loginArrayList.clear();

    arrayList.clear();

    arrayList = populateList();

    dataStore refreshHelper = new dataStore (this);
    SQLiteDatabase sqliteDatabase = refreshHelper.getWritableDatabase();
    Cursor cursor = sqliteDatabase.query(dataStore.TABLE_NAME_INFOTABLE, null, null, null, null, null, dataStore.COLUMN_NAME_SITE, null);
    String[]columns = new String[] { dataStore.COLUMN_NAME_SITE, dataStore.COLUMN_NAME_ADDRESS, dataStore.COLUMN_NAME_USERNAME, dataStore.COLUMN_NAME_PASSWORD, dataStore.COLUMN_NAME_NOTES };
    int[] to = new int[]{R.id.rusName, R.id.ruwUrl, R.id.ruuName, R.id.rupWord, R.id.ruNotes};
    SimpleCursorAdapter loginListAdapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_1, cursor, columns, to);
    loginListAdapter.notifyDataSetChanged();

}

@Override
public void onItemClick(AdapterView<?> arg0 , View arg1, int arg2, long arg3) {
    Toast.makeText(getApplicationContext(), "Selected ID :" + arg2, Toast.LENGTH_SHORT).show();

    Intent updateDeleteLoginInfo = new Intent (this, UpdateDeleteLoginList.class);



    LoginDetails clickedObject = loginArrayList.get(arg2);

        Bundle loginBundle = new Bundle();
    loginBundle.putString("clickedWebSite",clickedObject.getsName());
    loginBundle.putString("clickedWebAddress",clickedObject.getwUrl());
    loginBundle.putString("clickedUserName",clickedObject.getuName());
    loginBundle.putString("clickedPassWord",clickedObject.getpWord());
    loginBundle.putString("clickedNotes",clickedObject.getlNotes());

    updateDeleteLoginInfo.putExtras(loginBundle);

    startActivityForResult(updateDeleteLoginInfo, 0);       
       }    
          }

RennoDiniro 编辑结果:

日志:

       02-21 23:40:18.419: E/AndroidRuntime(705): FATAL EXCEPTION: main
       02-21 23:40:18.419: E/AndroidRuntime(705): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.loginplus.home/com.loginplus.home.LoginList}: java.lang.NullPointerException
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.ActivityThread.access$600(ActivityThread.java:123)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.os.Handler.dispatchMessage(Handler.java:99)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.os.Looper.loop(Looper.java:137)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.ActivityThread.main(ActivityThread.java:4424)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at java.lang.reflect.Method.invokeNative(Native Method)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at java.lang.reflect.Method.invoke(Method.java:511)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at dalvik.system.NativeStart.main(Native Method)
       02-21 23:40:18.419: E/AndroidRuntime(705): Caused by: java.lang.NullPointerException
       02-21 23:40:18.419: E/AndroidRuntime(705):   at com.loginplus.home.LoginList.populateList(LoginList.java:88)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at com.loginplus.home.LoginList.onCreate(LoginList.java:37)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.Activity.performCreate(Activity.java:4465)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
       02-21 23:40:18.419: E/AndroidRuntime(705):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

Activity 类:

      public class LoginList extends Activity implements OnClickListener,    OnItemClickListener {

      private ListView loginList;
      private Button webLogin;

      private ListAdapter loginListAdapter;

      private ArrayList<LoginDetails> loginArrayList;

      List<String> arrayList = new ArrayList<String>();

      @Override 
      public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);

      loginListAdapter = new ArrayAdapter<String>(this,   android.R.layout.simple_list_item_1, populateList());
      arrayList = populateList(); 
      setContentView(R.layout.login_listview);


      loginList = (ListView)
      findViewById(R.id.loginlist);
      loginList.setOnItemClickListener(this);

      webLogin = (Button)
      findViewById(R.id.button3);
      webLogin.setOnClickListener(this);
      }

      @Override
      public void onClick (View v) {
      Intent webLoginIntent = new Intent (this, LoginPlusActivity.class);
      startActivity(webLoginIntent);
      }

      public List<String> populateList (){

      List<String> webNameList = new ArrayList<String>();

      dataStore openHelperClass = new dataStore (this);

      SQLiteDatabase sqliteDatabase = openHelperClass.getReadableDatabase();

      Cursor cursor = sqliteDatabase.query(dataStore.TABLE_NAME_INFOTABLE, null, null, null, null, null, dataStore.COLUMN_NAME_SITE, null);

      startManagingCursor(cursor);


      while (cursor.moveToNext()){
      String sName = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_SITE));
      String wUrl = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_ADDRESS));
      String uName = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_USERNAME));
      String pWord = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_PASSWORD));
      String lNotes = cursor.getString(cursor.getColumnIndex(dataStore.COLUMN_NAME_NOTES));

    LoginDetails lpDetails = new LoginDetails();

   lpDetails.setsName(sName);
   lpDetails.setwUrl(wUrl);
   lpDetails.setuName(uName);
   lpDetails.setpWord(pWord);
   lpDetails.setlNotes(lNotes);

   loginArrayList.add(lpDetails);
   webNameList.add(sName);
   }

   sqliteDatabase.close();
   return webNameList;
    }

   @Override
   protected void onResume() {
    super.onResume();

    try{
    loginArrayList = new ArrayList<LoginDetails>();
    arrayList = new ArrayList<String>();
    loginArrayList.clear();
    arrayList.clear();

    arrayList = populateList();

    dataStore refreshHelper = new dataStore (this);
    SQLiteDatabase sqliteDatabase = refreshHelper.getWritableDatabase();
    Cursor cursor = sqliteDatabase.query(dataStore.TABLE_NAME_INFOTABLE, null, null, null, null, null, dataStore.COLUMN_NAME_SITE, null);
    String[]columns = new String[] { dataStore.COLUMN_NAME_SITE, dataStore.COLUMN_NAME_ADDRESS, dataStore.COLUMN_NAME_USERNAME, dataStore.COLUMN_NAME_PASSWORD, dataStore.COLUMN_NAME_NOTES };
     int[] to = new int[]{R.id.rusName, R.id.ruwUrl, R.id.ruuName, R.id.rupWord, R.id.ruNotes};
    SimpleCursorAdapter loginListAdapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_1, cursor, columns, to);
    loginListAdapter.notifyDataSetChanged();
     }catch(Exception e)
    {
   e.printStackTrace();
     }
    }
    @Override
    public void onItemClick(AdapterView<?> arg0 , View arg1, int arg2, long arg3) {
    Toast.makeText(getApplicationContext(), "Selected ID :" + arg2,    Toast.LENGTH_SHORT).show();

    Intent updateDeleteLoginInfo = new Intent (this, UpdateDeleteLoginList.class);



    LoginDetails clickedObject = loginArrayList.get(arg2);

    Bundle loginBundle = new Bundle();
    loginBundle.putString("clickedWebSite",clickedObject.getsName());
    loginBundle.putString("clickedWebAddress",clickedObject.getwUrl());
    loginBundle.putString("clickedUserName",clickedObject.getuName());
    loginBundle.putString("clickedPassWord",clickedObject.getpWord());
    loginBundle.putString("clickedNotes",clickedObject.getlNotes());

    updateDeleteLoginInfo.putExtras(loginBundle);

    startActivityForResult(updateDeleteLoginInfo, 0);   
   }
   }

Answer 1

使用指向所需数据和布局信息的光标创建适配器。

SimpleCursorAdapter mAdapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_1, cursor, columns, to);

在您使用 R.layout.simple_list_item_1

的情况下

columns 将为 null 或 您从游标获取的特定列数据

to 将是 android.R.id.text1

---

例如

  Cursor cursor = getContentResolver().query(People.CONTENT_URI, new String[]{People._ID, People.NAME, People.NUMBER}, null, null, null);
  startManagingCursor(cursor);
   // THE DESIRED COLUMNS TO BE BOUND

   String[] columns = new String[] { People.NAME, People.NUMBER };

  // THE XML DEFINED VIEWS WHICH THE DATA WILL BE BOUND TO
   int[] to = new int[] { R.id.name_entry, R.id.number_entry };

       SimpleCursorAdapter mAdapter = new SimpleCursorAdapter(this,R.layout.list_example_entry, cursor, columns, to);