sqlite数据库读取错误

Question

您好我正在从我的数据库中读取数据，它是使用sqlite管理器创建的，然后复制到我的应用程序的数据文件夹中，但当我尝试打印getcount时，游标返回零，我的代码中出现了什么错误是我的代码，这是错误

无法启动活动

ComponentInfo {your.pckage.namespac/your.pckage.namespac.TabarActivity}，第二个错误

引起：显示java.lang.NullPointerException

public class DBHelper { 
public static final String KEY_ROWID = "id"; 
public static final String KEY_NAME = "name"; 
public static final String SMALL = "small"; 
public static final String LARGE = "large"; 
public static final String TYPE1 = "type1"; 
public static final String TYPE2 = "type2"; 
public static final String TYPE3 = "type3"; 
public static final String TEX = "tex"; 
public static final String ORIGIN = "origin"; 
public static final String DESCRIPTION = "description"; 
public static final String BOOKMARK = "bookmark"; 

public static final String KEY_EMAIL = "email"; 
private static final String TAG = "DBAdapter"; 

private static final String DATABASE_NAME = "vegetable.db"; 
private static final String DATABASE_TABLE = "mac"; 
private static final int DATABASE_VERSION = 2; 


private static final String DATABASE_CREATE ="create table mac (id integer primary key autoincrement not null ,"+ 
      "name VARCHAR, small integer,"+ 
      "large integer, type1 integer,"+ 
      "type2 integer, type3 integer,"+ 
      "tex varchar, origin varchar,"+ 
      "description varchar, bookmark varchar);"; 

private final Context context;  

private DatabaseHelper DBHelper; 
private SQLiteDatabase db; 

public DBHelper(Context ctx) 
{ 
    this.context = ctx; 
    DBHelper = new DatabaseHelper(context); 
} 

private static class DatabaseHelper extends SQLiteOpenHelper 
{ 
    DatabaseHelper(Context context) 
    { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) 
    { 
     try { 
      db.execSQL(DATABASE_CREATE);  
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    { 
     Log.w(TAG, "Upgrading database from version " + oldVersion + " to " 
       + newVersion + ", which will destroy all old data"); 
     db.execSQL("DROP TABLE IF EXISTS contacts"); 
     onCreate(db); 
    } 
}  

//---opens the database--- 
public DBHelper open() throws SQLException 
{ 
    //db = DBHelper.getWritableDatabase(); 
    db=DBHelper.getReadableDatabase(); 
    return this; 
} 

//---closes the database---  
public void close() 
{ 
    DBHelper.close(); 
} 


//---deletes a particular contact--- 
public boolean deleteContact(long rowId) 
{ 
    return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0; 
} 

//---retrieves all the contacts--- 
public Cursor getAllContacts() 
{ 
    return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME, 
      SMALL,LARGE,TYPE1,TYPE2,TYPE3,TEX,ORIGIN,DESCRIPTION,BOOKMARK}, null, null, null, null, null); 
} 

//---retrieves a particular contact--- 
public Cursor getContact(long rowId) throws SQLException 
{ 

    Cursor mCursor = 
      db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID, 
        SMALL,LARGE,TYPE1,TYPE2,TYPE3, 
        TEXTURE,ORIGIN,DESCRIPTION,BOOKMARK}, KEY_ROWID + "=" + rowId, null, 
      null, null, null, null); 
    System.out.println(mCursor); 
    if (mCursor != null) { 
     System.out.println(1); 
     //Boolean t=mCursor.moveToFirst(); 
     Boolean t=mCursor.moveToNext(); 
     System.out.println(t); 
    } 
    return mCursor; 
} 

//---updates a contact--- 
public boolean updateContact(long rowId, String secondview) 
{ 
    ContentValues args = new ContentValues(); 

    args.put(KEY_NAME, secondview); 
    return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; 
} 
} 




public class MyListActivity extends ActivityGroup { 




/** Called when the activity is first created. */ 

String tag = "Events"; 
String[] presidents; 
String[] ima; 
int i=0; 
Intent intent; 

Integer[] imageIDs= {R.drawable.abbaysmall,R.drawable.edalesmall}; 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.listtype); 
    try {   
     String destPath = "/data/data/" + getPackageName() + "/databases/vegetable.db"; 
     File f = new File(destPath);    
     if (!f.exists()) {   
      CopyDB(getBaseContext().getAssets().open("vegetable.db"), 
       new FileOutputStream(destPath)); 
      System.out.println("hi"); 
     } 
    } catch (FileNotFoundException e) {   
     e.printStackTrace(); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
    DBHelper db = new DBHelper(this); 



    //---get a contact--- 
    db.open(); 
    Cursor c = db.getContact(1); 

    System.out.println(c.getCount()); 


    if (c.moveToFirst()){ 


     }else 
     { 
     Toast.makeText(this, "No contact found", Toast.LENGTH_LONG).show(); 
    db.close(); 
    } 




    list.setAdapter(adapter); 
    //setListAdapter(adapter); 
    list.setOnItemClickListener(onListClick); 

} 
public void CopyDB(InputStream inputStream, OutputStream outputStream) 
     throws IOException { 
      //---copy 1K bytes at a time--- 
      byte[] buffer = new byte[1024]; 
      int length; 
      while ((length = inputStream.read(buffer)) > 0) { 
       outputStream.write(buffer, 0, length); 
      } 
      inputStream.close(); 
      outputStream.close(); 
     } 


} 

Answer 1

这些代码是否会打印任何消息？（在您的getContact方法中）是mCursor null？

if (mCursor != null) { 
    System.out.println(1); 
    //Boolean t=mCursor.moveToFirst(); 
    Boolean t=mCursor.moveToNext(); 
    System.out.println(t); 
} 

编辑：试试这个吗？从系统ContentProvider加载图像信息

private final Uri PHOTO_URI = MediaStore.Images.Media.EXTERNAL_CONTENT_URI; 
private final String[] PHOTO_PJT = new String[] { 
     MediaStore.Images.Media._ID, MediaStore.Images.Media.DATA, 
     MediaStore.Images.Media.DATE_TAKEN, MediaStore.Images.Media.SIZE, 
     MediaStore.Images.Media.DESCRIPTION, MediaStore.Images.Media.TITLE, 
     MediaStore.Images.Media.MIME_TYPE }; 
ContentResolver mResolver = mContext.getContentResolver(); 
Cursor c = mResolver.query(PHOTO_URI, PHOTO_PJT, null, null, TITLESEARC);