Question

我试图从数据库中获取数据到listview.i必须在我的dbhelper类中使用表。一个是登录数据表，另一个是数据存储表。从该表中，我将数据提取到listview。请在这里找到我的代码并告诉我这里有什么问题。我的log cat在getAllValues（）方法中显示nullpoint异常。请帮我。

public class DbHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "sri.db";
private static final int DATABASE_VERSION = 1;
public static final String TABLE_NAME = "login";
private static final String TABLE_CREATE ="CREATE TABLE " + TABLE_NAME + "(" +
   "_id INTEGER PRIMARY KEY AUTOINCREMENT,"+
   "username TEXT NOT NULL, password TEXT NOT NULL);";

private static final String DB_ADMIN = "INSERT INTO "+TABLE_NAME+"values(1, admin,                 password);";

public static final String TABLE_NAME_SAVE="saveinfo";
public static final String KEY_ID="_id";
public static final String KEY_URL="surl";
public static final String KEY_UID="suid";
public static final String KEY_PASS="spassword";

public static final String SCRIPT="CREATE TABLE" + TABLE_NAME_SAVE + "(" + "_id INTEGER PRIMARY KEY AUTOINCREMENT,"+
"surl TEXT NOT NULL, suid TEXT NOT NULL, spassword TEXT NOT NULL);";



public DbHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    System.out.println("In constructor");
}

@Override
public void onCreate(SQLiteDatabase db) {
    try{
        //Create Database
        db.execSQL(TABLE_CREATE);
        //create admin account
        db.execSQL(DB_ADMIN);
        //System.out.println("In onCreate");
        db.execSQL(SCRIPT);
    }catch(Exception e){
    e.printStackTrace();
    }



}


     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    onCreate(db);

}
       SQLiteDatabase db;

   public Cursor getAllValues() {
// TODO Auto-generated method stub
String[] clumns={KEY_ID,KEY_URL,KEY_UID,KEY_PASS};
return db.query(TABLE_NAME_SAVE, clumns, null, null, null, null, null);
  }

   void deleteAllRecords(){
  db.delete(TABLE_NAME_SAVE, null, null);
 }




 void deleteOneRecord(String rowid){
  db.delete(TABLE_NAME_SAVE, rowid +"="+KEY_ID, null);
 }

public void openDatabase() {
    // TODO Auto-generated method stub

}



 }

这是我的 DbHelper calss

这是我的 DisplayActivity .java calss

public class DisplayActivity extends Activity implements OnItemLongClickListener {

DbHelper db=new DbHelper(this);
Cursor cursor;
ListView list;
private int position;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_display);
    db.openDatabase();
    list = (ListView) findViewById(R.id.lvf);

     //updateListView();
      list.setOnItemLongClickListener(this);
}



class CustomAdapter extends BaseAdapter {

      @Override
      public int getCount() {
       // TODO Auto-generated method stub
       return cursor.getCount();
      }

      @Override
      public Object getItem(int arg0) {
       // TODO Auto-generated method stub
       return null;
      }

      @Override
      public long getItemId(int arg0) {
       // TODO Auto-generated method stub
       return 0;
      }

      @Override
      public View getView(int position, View view, ViewGroup arg2) {
       // TODO Auto-generated method stub
       view = getLayoutInflater().inflate(R.layout.details, null);

       TextView t0 = (TextView) view.findViewById(R.id.did);
       TextView t1 = (TextView) view.findViewById(R.id.durl);
       TextView t2 = (TextView) view.findViewById(R.id.duid);
       TextView t3 = (TextView) view.findViewById(R.id.dpass);

       cursor.moveToPosition(position);

       String rowid = cursor.getString(0);
       String url = cursor.getString(1);
       String uid = cursor.getString(2);
       String pass=cursor.getString(3);

       t0.setText(rowid);
       t1.setText(url);
       t2.setText(uid);
       t3.setText(pass);
       return view;
      }

     }


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.display, menu);
    return true;
}
void updateListView() {
    // TODO Auto-generated method stub
    cursor = db.getAllValues();
      CustomAdapter cs = new CustomAdapter();
      list.setAdapter(cs);


}

@Override
public boolean onItemLongClick(AdapterView<?> arg0, View arg1, int pos,
        long arg3) {
    // TODO Auto-generated method stub
    this.position=pos;
    return false;
}

}

Answer 1

使用游标适配器参见下面的示例：

public class ContactCursorAdapterCT extends CursorAdapter {
       public ContactCursorAdapterCT(Context context, Cursor c) {
    super(context, c);
    // TODO Auto-generated constructor stub
}

@Override
public void bindView(View view, Context context, Cursor cursor) {

    while (cursor.moveToNext()) {

    TextView name = (TextView)view.findViewById(R.id.blacklistDB1);               
          name.setText(cursor.getString(cursor.getColumnIndex
          (ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME)));

          TextView phone = (TextView)view.findViewById(R.id.blacklistDB2); 
          phone.setText(cursor.getString(cursor.getColumnIndex
          (ContactsContract.CommonDataKinds.Phone.NUMBER)));

}
}

@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
    // TODO Auto-generated method stub

    LayoutInflater inflater = LayoutInflater.from(context);

    View v = inflater.inflate(R.layout.lv, parent, false);
            bindView(v, context, cursor);
           return v;
        }

Answer 2

您未在db方法中初始化DbHelper。从类字段中删除它，那里不需要它。您应该按照getAllValues()方法启用它，如下所示：

public Cursor getAllValues() {
    // TODO Auto-generated method stub
    SQLiteDatabase db = this.getWritableDatabase();
    String[] clumns={KEY_ID,KEY_URL,KEY_UID,KEY_PASS};
    return db.query(TABLE_NAME_SAVE, clumns, null, null, null, null, null);

}

顺便说一下，最好为SQLiteOpenHelper使用单身人士。在这种情况下，您可以通过`SQLiteDatabase db = getWritableDatabase（）;

在所有方法中获取数据库

如何从数据库获取数据到listview

2 个答案: