我在一个项目中，我有一个包含 2 个或更多表 n 很多条目的数据库。所以我使用 sqlite 来创建这个数据库。正如我在其他几个答案中所读到的，我将不得不将数据库文件复制到资产文件夹中。现在我在资产文件夹中有数据库文件。这是我用于 DataBaseHelperClass 的代码
package com.example.basic;
import java.io.File;
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.SQLiteOpenHelper;
import android.util.Log;
public class DataBaseHelperClass extends SQLiteOpenHelper {
private static String TAG = "DataBaseHelperClass";
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.example.astro/databases/";
// Data Base Name.
private static final String DATABASE_NAME = "MyDatabase.sqlite";
// Data Base Version.
private static final int DATABASE_VERSION = 1;
// Table Names of Data Base.
static final String TABLE_Name = "Totlist";
public Context context;
static SQLiteDatabase sqliteDataBase;
public DataBaseHelperClass(Context context) {
super(context, DATABASE_NAME, null ,DATABASE_VERSION);
this.context = context;
}
public void createDataBase() throws IOException{
//check if the database exists
boolean databaseExist = checkDataBase();
if(databaseExist){
// Do Nothing.
}else{
this.createDataBase();
copyDataBase();
}// end if else dbExist
} // end createDataBase().
public boolean checkDataBase(){
File databaseFile = new File(DB_PATH + DATABASE_NAME);
return databaseFile.exists();
}
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = context.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 input file to the output file
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();
}
/**
* This method opens the data base connection.
* First it create the path up till data base of the device.
* Then create connection with data base.
*/
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DATABASE_NAME;
sqliteDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
/**
* This Method is used to close the data base connection.
*/
public synchronized void close() {
if(sqliteDataBase != null)
sqliteDataBase.close();
super.close();
}
public String getUserNameFromDB(){
String query = "select desc From "+TABLE_Name;
Cursor cursor = sqliteDataBase.rawQuery(query, null);
String description = null;
if(cursor.getCount()>0){
if(cursor.moveToFirst()){
do{
description = cursor.getString(0);
}while (cursor.moveToNext());
}
}
return description;
}
public String tot(){
String rawQuery = "SELECT tot from Totlist WHERE Tid=1";
Cursor cursor = sqliteDataBase.rawQuery(rawQuery, null);
String desc=null;
if(cursor.getCount()>0){
if(cursor.moveToFirst()){
do{
desc=cursor.getString(0);
}while(cursor.moveToNext());
}
}
return desc;
}
public String chq()
{
String q="hee";
return q;
}
public void onCreate(SQLiteDatabase db) {
// No need to write the create table query.
// As we are using Pre built data base.
// Which is ReadOnly.
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// No need to write the update table query.
// As we are using Pre built data base.
// Which is ReadOnly.
// We should not update it as requirements of application.
}
}
这在 logcat 中显示了很多错误。其中之一是“错误打开跟踪文件：没有这样的文件或目录 (2)”。问题可能是资产中的文件没有复制到默认位置 n 因此它说没有这样的文件或目录。这是我关于这个数据库的第二个问题，我仍然无法从中得到结果。我的 mainactivity 中的代码是这样的。
package com.example.basic;
import android.os.Bundle;
import android.app.Activity;
import android.database.Cursor;
import android.text.Editable;
import android.view.Menu;
import android.widget.TextView;
public class Basic extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.basic);
DataBaseHelperClass db = new DataBaseHelperClass(this);
String s=db.chq();
TextView tv=(TextView)findViewById(R.id.TextView1);
tv.setText(s);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.basic, menu);
return true;
}
}
我的项目中只有这两个 .java 文件。这有什么问题吗？