問題從數據庫中顯示的數據

Question

數據庫：

IM試圖從一個數據庫中的數據在ListView顯示出來，但它不會顯示出來。它強制關閉，所以我看着Logcat，它說我的populateFrom()和bindView()是零點例外，但我不認爲這是問題。然後我嘗試調試它們，我注意到它來自我認爲的query()。因爲它的鏈接與查詢多數民衆贊成爲什麼該方法不能工作，從而顯示錯誤？也許。

我嘗試搜索有用的資源，但他們的查詢與我的查詢幾乎相同。我現在升職了。誰能幫我。？這只是顯示數據庫中所有data(food)的名稱。我檢查並且沒有拼寫錯誤。 （

TestDatabaseMain.java：

public class TestDatabaseMain extends Activity 
{ 

    private ListViewHelperTest dbListFoodHelper = null; 
    private Cursor OurCursor = null; 
    private ListFoodAdapter adapter=null; 

    public void onCreate(Bundle savedInstanceState) 
    { 
     try 
     { 
      super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 

     ListView myListView = (ListView)findViewById(R.id.listfood); 

     //create the database helper 
     dbListFoodHelper=new ListViewHelperTest(this);  
     //create the database if user runs the first time 
     dbListFoodHelper.createDataBase(); 

     dbListFoodHelper.openDataBase(); 

     OurCursor=dbListFoodHelper.getCursor(); 

     startManagingCursor(OurCursor); 

     adapter = new ListFoodAdapter(OurCursor); 

     myListView.setAdapter(adapter); 

     } 
     catch(Exception e) 
     { 
      Log.e ("ERROR","ERROR IN CODE: " + e.toString()); 

      e.printStackTrace(); 
     } 
    } 

    class ListFoodAdapter extends CursorAdapter 
    { 
     ListFoodAdapter(Cursor c) 
     { 
      super(TestDatabaseMain.this, c); 
     } 

     @Override 
     public void bindView(View row, Context ctxt, Cursor c) 
     { 
      ListFoodHolder holder = (ListFoodHolder)row.getTag(); 
      holder.populateFrom(c, dbListFoodHelper); 
     } 

     @Override 
     public View newView(Context ctxt, Cursor c, ViewGroup parent) 
     { 
      LayoutInflater inflater =getLayoutInflater(); 
      View row = inflater.inflate(R.layout.row, parent, false); 
      ListFoodHolder holder = new ListFoodHolder(row); 
      row.setTag(holder); 
      return(row); 
     } 
    } 

    static class ListFoodHolder 
    { 
     private TextView name = null; 

     ListFoodHolder(View displayfood) 
     { 
      name = (TextView)displayfood.findViewById(R.id.listfood); 
     } 

     public void populateFrom(Cursor c, ListViewHelperTest r) 
     {  
      //to list out the data from the database 
      name.setText(r.getName(c)); 
     } 
    } 

ListViewHelperTest.java：

public class ListViewHelperTest extends SQLiteOpenHelper 
{ 


    //declare constants of the paths 
    private static String DB_PATH = "/data/data/sg.edu.tp.iit.mns/databases/"; 
    private static String DB_NAME = "ListFoodItem"; 
    private static int SCHEMA_VERSION=1; 

    private static final String TABLE_NAME = "listfooditem"; 
    private static final String FOOD_TITLE = "FoodItem"; 
    private static final String FOOD_ID = "_id"; 


    private SQLiteDatabase myDataBase; 
    private final Context myContext; 

    public ListViewHelperTest(Context context) 
    { 
     super(context, DB_NAME, null, SCHEMA_VERSION); 
     this.myContext = context; 
     // TODO Auto-generated constructor stub 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) 
    { 
     // TODO Auto-generated method stub 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    { 
     // TODO Auto-generated method stub 
    } 

    public void createDataBase() 
    { 
     createDB(); 
    } 

    public void createDB() 
    { 
     boolean dbExist = DBExists(); 


     if (!dbExist) 
     { 
      //overwrite the database with the previous database 
      this.getReadableDatabase(); 

      //copy the overwrite 
      copyDBFromRecource(); 

     } 
    } 

    private boolean DBExists() 
    { 

     SQLiteDatabase checkDB = null; 

     try 
     { 
      String myPath = DB_PATH + DB_NAME; 
      checkDB = SQLiteDatabase.openDatabase(myPath, null, 
        SQLiteDatabase.OPEN_READWRITE); 
      checkDB.setLocale(Locale.getDefault()); 
      checkDB.setLockingEnabled(true); 
      checkDB.setVersion(1); 
     } 

     catch(SQLiteException e) 
     { 
      Log.e("SqlHelper","database not found"); 
     } 


     if(checkDB != null) 
     { 
      checkDB.close(); 
     } 

     return checkDB != null ? true : false; 
    } 

    private void copyDBFromRecource() 
    { 
     InputStream myInput=null; 

     // Path to the just created empty db 

     try 
     { 
      //Open your local db as the input stream 
      myInput = myContext.getAssets().open(DB_NAME); 

      OutputStream myOutput=null; 
      // Path to the just created empty db 
      String outFileName = DB_PATH + DB_NAME; 

      //Open the empty db as the output stream 
      myOutput = new FileOutputStream(outFileName); 

      //transfer bytes from the inputfile to the outputfile 
      byte[] buffer = new byte[1024]; 
      int length; 
      while ((length = myInput.read(buffer))>0) 
      { 
       myOutput.write(buffer, 0, length); 
      } 

      //Close the streams 
      myOutput.flush(); 
      myOutput.close(); 
      myInput.close(); 
     } 
     catch (Exception e) 
     { 
      throw new Error("Problem coping folders"); 
     } 

    } 
    public void openDataBase() throws SQLException 
    { 
     String MyPath = DB_PATH + DB_NAME ; 
     myDataBase = SQLiteDatabase.openDatabase(MyPath, null, 
       SQLiteDatabase.OPEN_READWRITE); 
    } 

    @Override 
    public synchronized void close() 
    { 
     if (myDataBase != null) 
     { 
      myDataBase.close(); 
     } 
     super.close(); 
    } 
    //important! 
    public Cursor getCursor() 
    { 
     SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder(); 

     queryBuilder.setTables(TABLE_NAME); 

     String[] ColumnReturn = new String[] {FOOD_ID, FOOD_TITLE}; 

     //search by string pass(*important*) 
     Cursor MYCursor = queryBuilder.query(myDataBase, ColumnReturn, null, 
       null, null, null, "FoodItem ASC");  
     return MYCursor; 
    } 

    public String getName(Cursor c) 
    { 
     return(c.getString(1)); 
    } 
} 

Answer 1

嘗試調用Cursor.moveToFirst（）;你的光標用它做任何事情之前