如何从Android上的SQLite数据库检索数据？ [英] How do I retrieve data from an SQLite database on Android?
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问题描述
我正在使用的资产/数据库文件夹，我自己的数据的基础上，我已经给了路径的.java文件DATABSE，
I am using my own data base in "asset/database" folder, I have given the path in .java databse file,
我想执行的启动按钮和code中的活动是：
I want to perform the activity on start button and the code is :
GreTest.java
GreTest.java
package andro.Alkonsys.example;
import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.TextView;
import andro.Alkonsys.example.DataBaseHelper;
public class GreTest extends Activity {
public Button start_test1;
public Button next;
public TextView Question;
public RadioButton Option_first;
public RadioButton Option_second;
public RadioButton Option_third;
public RadioButton Option_forth;
private DataBaseHelper db;
@Override
public void onCreate(Bundle SaveInstanceState)
{
super.onCreate(SaveInstanceState);
setContentView(R.layout.gretest);
start_test1=(Button)findViewById(R.id.btnstart_test);
next=(Button)findViewById(R.id.btnnextquastion);
Question=(TextView)findViewById(R.id.testquestion);
Option_first=(RadioButton)findViewById(R.id.radio_first);
Option_second=(RadioButton)findViewById(R.id.radio_second);
Option_third=(RadioButton)findViewById(R.id.radio_third);
Option_forth=(RadioButton)findViewById(R.id.radio_forth);
start_test1.setOnClickListener(new OnClickListener()
{
//int Qno;
//Cursor c;
public void onClick(View v){
// TODO Auto-generated method stub
Cursor c = db.getData();
//if(c.moveToFirst())
//{
Question.setText(c.getString(2));
//Option_first.setText(c.getString(3));
//}
//Qno += 1;
}
});
}
}
/* private OnClickListener radio_listener = new OnClickListener() {
public void onClick(View v) {
// Perform action on clicks
RadioButton rb = (RadioButton) v;
Toast.makeText(GreTest.this, rb.getText(), Toast.LENGTH_SHORT).show();
}}; */
和我的数据库文件，让所有的查询和声明：
and my database file is having all queries and declaration :
DataBaseHelper.java
DataBaseHelper.java
package andro.Alkonsys.example;
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/+andro.Alkonsys.example()+/Database/";
private static final String DATABASE_NAME ="GreSatDbase";
//The version of the database that this class understands
private static final int DATABASE_VERSION = 1;
//private SQLiteDatabase myDataBase;
private final Context myContext;
private SQLiteDatabase db;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DataBaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
myContext = context;
}
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DATABASE_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;
}
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DATABASE_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DATABASE_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 + DATABASE_NAME;
db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(db != null)
db.close();
super.close();
}
@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
String sql = myContext.getString(R.string.satgreDbase_onUpgrade);
db.beginTransaction();
try
{
db.execSQL(sql);
db.setTransactionSuccessful();
}catch(SQLException e)
{
System.out.println("Error Upgrading tables...");
}
finally
{
db.endTransaction();
}
onCreate(db);
}
public Cursor getData()
{
int Qno=1;
// TODO Auto-generated method stub
//Creates the query String. Query is static in DataCursor inner class
String sql = "SELECT Question FROM PracTestAlgebra WHERE Qno = ?";
//Create an array of String to specify values for ?'s in the sql Query
String sqlArgs[] = new String[]{Integer.toString(Qno)};
//Creates a cursor using the SQLiteDatabase object's rawQuery method
Cursor c = db.rawQuery(sql,sqlArgs);
//The cursor is returned
return c;
}
}
和我想从我的数据库retive的数据，所以请帮我这一点。
and I want to retive the data from my database, so please help me for that.
谢谢...
推荐答案
另外，我遇到了应用这一技术的错误：如果您的SQL文件比1Mo钢越多，你的应用程序将无法阅读它。这是因为Android的automaticaly COM presses的资产目录大文件，并没有流中读取它们。
Also, I met a bug applying this technique: if your sql file is more than 1Mo, your app will fail reading it. It's because android automaticaly compresses large files in assets dir, and fails to stream read them.
我发现，要克服这种错误的最简单方法是扩展名为后缀的SQL文件一个COM pressed文件：data.sql - > data.sql.mp3
I found that the easiest way to overcome this bug is to suffix your sql file with the extension a compressed file : data.sql -> data.sql.mp3.
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