Question

我在db上填写了 listview 。我想在 listview 中搜索。我想在listview上的列表后搜索名称，姓氏和公司字段。此代码返回 NullPointerException 。

myhomeclass：

@SuppressWarnings("deprecation")
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(R.layout.asrehber);

    dbHelper = new DBAdapter(this);
    dbHelper.open();

    Cursor cursor = dbHelper.getAllPerson();
    String[] from = new String[] { DBAdapter.KEY_NAME,
            DBAdapter.KEY_SURNAME, DBAdapter.KEY_COMPANY };
    int[] to = new int[] { R.id.btnUserNameListItem,
            R.id.btnUserSurnameNameListItem };

    dataAdapter = new SimpleCursorAdapter(this,
            R.layout.asrehber_single_list_item, cursor, from, to);

    ListView listView = (ListView) findViewById(R.id.listViewMain);
    listView.setAdapter(dataAdapter);

    dbHelper.close();

    listView.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            Intent viewCon = new Intent(ASRehber.this, PersonProfile.class);
            viewCon.putExtra(ROW_ID, id);
            startActivity(viewCon);
            finish();
        }
    });



    // Custom Search/////////////

    edtxtSearch = (EditText) findViewById(R.id.edtxtSearch);
    edtxtSearch.addTextChangedListener(new TextWatcher() {

        @Override
        public void onTextChanged(CharSequence s, int start, int before,
                int count) {
             ASRehber.this.dataAdapter.getFilter().filter(s);
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count,
                int after) {
            // TODO Auto-generated method stub

        }

        @Override
        public void afterTextChanged(Editable s) {
            // TODO Auto-generated method stub

        }
    });

}

mydataadapter：

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {

public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "name";
public static final String KEY_SURNAME = "surname";
public static final String KEY_COMPANY = "company";
public static final String KEY_EMAIL = "email";
public static final String KEY_PHONE = "phone";

private static final String TAG = "DBAdapter";
private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;

private static final String DATABASE_NAME = "ASRehber";
private static final String DATABASE_TABLE = "Person";
private static final int DATABASE_VERSION = 1;

public static final String[] ALL_KEYS = new String[] { KEY_ROWID, KEY_NAME,
        KEY_SURNAME, KEY_COMPANY, KEY_EMAIL, KEY_PHONE };

private final Context mCtx;

private static final String DATABASE_CREATE = "CREATE TABLE if not exists "
        + DATABASE_TABLE + " (" + KEY_ROWID
        + " integer PRIMARY KEY autoincrement," + KEY_NAME + ","
        + KEY_SURNAME + "," + KEY_COMPANY + "," + KEY_EMAIL + ","
        + KEY_PHONE + ");";

private static class DatabaseHelper extends SQLiteOpenHelper {

    DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        Log.w(TAG, DATABASE_CREATE);
        db.execSQL(DATABASE_CREATE);

    }

    @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 " + DATABASE_TABLE);
        onCreate(db);
    }
}

public DBAdapter(Context ctx) {
    this.mCtx = ctx;
}

public DBAdapter open() throws SQLException {
    mDbHelper = new DatabaseHelper(mCtx);
    mDb = mDbHelper.getWritableDatabase();
    return this;
}

public void close() {
    if (mDbHelper != null) {
        mDbHelper.close();
    }
}

public Cursor getAllPerson() {
    String where = null;
    Cursor c = mDb.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null,
            null, null, null);
    if (c != null) {
        c.moveToFirst();
    }
    return c;
}

// Get a specific row (by rowId)
public Cursor getPerson(long rowId) {
    String where = KEY_ROWID + "=" + rowId;
    Cursor c = mDb.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null,
            null, null, null);
    if (c != null) {
        c.moveToFirst();
    }
    return c;
}

public long insertPerson(String name, String surname, String company,
        String email, String phone) {

    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_NAME, name);
    initialValues.put(KEY_SURNAME, surname);
    initialValues.put(KEY_COMPANY, company);
    initialValues.put(KEY_EMAIL, email);
    initialValues.put(KEY_PHONE, phone);

    return mDb.insert(DATABASE_TABLE, null, initialValues);
}

public boolean deletePerson(long rowId) {

    String where = KEY_ROWID + "=" + rowId;
    return mDb.delete(DATABASE_TABLE, where, null) != 0;
}



public boolean updateRow(long rowId, String name, String surname,
        String company, String email, String phone) {
    String where = KEY_ROWID + "=" + rowId;
    ContentValues newValues = new ContentValues();
    newValues.put(KEY_NAME, name);
    newValues.put(KEY_SURNAME, surname);
    newValues.put(KEY_COMPANY, company);
    newValues.put(KEY_EMAIL, email);
    newValues.put(KEY_PHONE, phone);
    // Insert it into the database.
    return mDb.update(DATABASE_TABLE, newValues, where, null) != 0;
}

}

Answer 1

嗯，这很简单。 dbHelper.getAllPerson();如果找不到任何匹配数据，则有可能返回null。你只需要处理它。

Answer 2

1）不要关闭数据库，直到你不再需要它的任何一个游标。 SimpleCursorAdapter（以及几乎所有使用游标的东西）并不会将所有数据保存在内存中，而是在需要时会查询它的新行（例如，当用户滚动列表或尝试过滤时列表）。而是使用它在onDestory() Activity方法中关闭数据库。

2）当您关闭某些内容（光标，数据库，流 - 任何内容）时，请在finally {}块中执行此操作。

3）你真的应该考虑在ContentProvider中使用存储数据并使用Loaders来访问它 - 这种方法使数据库访问变得更加简单，并避免长时间SQL查询拖延主线程。

如何在数据库中填充的listview中搜索？

2 个答案: