我创建了一个包含这样信息的数据库 http://i170.photobucket.com/albums/u244/therealbbri06/database.jpg
我正在尝试使用此
从数据库中获取groupName
public String readNameFromPosition(int position) {
Cursor c;
c = myDataBase.query("hikingGroups", new String[] { "groupName" },
"position=\'" + position + "\'", null, null, null, null);
if (c.moveToFirst()) {
return c.getString(0);
} else {
return "" + c.getCount();
}
}
当position = 0时，正确检索groupName，但只要该位置等于任何其他有效数字，c.getCount（）将返回“0”。有帮助吗？如果需要，我可以发布更多代码，请问。 readNameFromPosition（）也在我的DataBaseHelper类中。
更新：我的代码
package bry.Bicker.OjaiHiking;
import java.io.IOException;
import android.app.Activity;
import android.database.SQLException;
import android.graphics.Typeface;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.Gallery;
import android.widget.TextView;
import android.widget.Toast;
public class OjaiHikingActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final DataBaseHelper theDb = new DataBaseHelper(getApplicationContext());
try {
theDb.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
theDb.openDataBase();
} catch (SQLException sqle) {
throw sqle;
}
final Gallery hikesGallery = (Gallery) findViewById(R.id.gallery1);
hikesGallery.setAdapter(new ImageAdapter(this));
hikesGallery.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
String groupName = "";
int position = hikesGallery.getSelectedItemPosition();
Toast.makeText(getApplicationContext(), "" + position,
Toast.LENGTH_SHORT).show();
groupName = theDb.readNameFromPosition(position);
TextView tV = (TextView) findViewById(R.id.groupName);
Typeface font = Typeface.createFromAsset(getAssets(),
"arialbd.ttf");
tV.setTypeface(font);
tV.setText(groupName);
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
}
});
hikesGallery.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView parent, View v, int position,
long id) {
}
});
}
}
DataBaseHelper.java的代码
package bry.Bicker.OjaiHiking;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DataBaseHelper extends SQLiteOpenHelper {
// The Android's default system path of your application database.
private static String DB_PATH = "/data/data/bry.Bicker.OjaiHiking/databases/";
private static String DB_NAME = "Ojaiker.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
public DataBaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
// do nothing - database already exist
} else {
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each
* time you open the application.
*
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
// database does't exist yet.
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created
* empty database in the system folder, from where it can be accessed and
* handled. This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException {
// Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
// Open the empty db as the output stream
OutputStream 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();
}
public void openDataBase() throws SQLException {
// Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if (myDataBase != null)
myDataBase.close();
super.close();
}
public String readNameFromPosition(int position) {
Cursor c;
c = myDataBase.query("hikingGroups", new String[] { "groupName" },
"position=\'" + position + "\'", null, null, null, null);
if (c.moveToFirst()) {
return c.getString(0);
} else {
return "" + c.getCount();
}
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
答案 0 :(得分：1)
您确定没有使用应用程序之外的值更新数据库（例如在SQLite管理器中），然后运行应用程序，假设新值将在新运行中出现？您的数据库不会再使用设备/模拟器上的新值进行构建。
尝试重新安装应用程序，然后重新安装（一个疯狂的猜测是，您首先使用一个值启动数据库（对于位置0））。
答案 1 :(得分：0)
public String readNameFromPosition(int position) {
Cursor c;
public static final String KEY_ROWID="id";
public static final String KEY_POSITION="position";
public static final String KEY_GROPUNAME="groupName";
String[] col=new String[]{KEY_ROWID,KEY_POSITION,KEY_GROPUNAME};
Cursor c=ourDatabase.query("hikingGroups", col,KEY_POSITION+"="+position, null, null, null, null);
if (c!=null) {
c.moveToFirst();
return c.getString(c.getColumnIndex(KEY_GROPUNAME));
} else {
return "" + c.getCount();
}
}
试试这种方式
答案 2 :(得分：0)
我认为数据库查询没有返回任何结果。 c.moveToFirst（）必须返回false，因此你不应该做c.getString（...）
更好的处理方式
if (c.moveToFirst()) {
return c.getString(c.getColumnIndex(KEY_GROPUNAME));
} else {
return "" + c.getCount();
}