android - 应用程序启动时数据库不可用

Question

我的应用程序的数据库有问题。数据库应该在我的应用程序启动时可用，但是目前数据库只会在我输入需要插入数据库的数据时出现在 ddms 上，这是不正确的。有人对解决我的问题有想法吗？任何帮助将不胜感激！提前致谢。

Answer 1

在您的应用程序启动时，您需要检查数据库是否已经存在于 ddms 中。如果数据库存在，那么您必须对其进行配置，以便之后一切都会好起来

这是完整的代码..

package com.MyPackage;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;

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;
import android.util.Log;

public class AnyDBAdapter {

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

//make sure this matches the 
//package com.MyPackage;
//at the top of this file
private static String DB_PATH = "/data/data/com.MyPackage/databases/";

//make sure this matches your database name in your assets folder
// my database file does not have an extension on it 
// if yours does
// add the extention
private static final String DATABASE_NAME = "data";

//Im using an sqlite3 database, I have no clue if this makes a difference or not
private static final int DATABASE_VERSION = 3;

private final Context adapterContext;

public AnyDBAdapter(Context context) {
    this.adapterContext = context;
}

public AnyDBAdapter open() throws SQLException {
    mDbHelper = new DatabaseHelper(adapterContext);

    try {
        mDbHelper.createDataBase();
    } catch (IOException ioe) {
        throw new Error("Unable to create database");
    }

    try {
        mDbHelper.openDataBase();
    } catch (SQLException sqle) {
        throw sqle;
    }
    return this;
}
//Usage from outside
// AnyDBAdapter dba = new AnyDBAdapter(contextObject); //in my case contextObject is a  map
// dba.open();
// Cursor c = dba.ExampleSelect("Rawr!");
// contextObject.startManagingCursor(c);
// String s1 = "", s2 = "";
// if(c.moveToFirst())
// do {
//  s1 = c.getString(0);
//  s2 = c.getString(1);
//  } while (c.moveToNext());
// dba.close();
public Cursor ExampleSelect(string myVariable)
{
    String query = "SELECT locale, ? FROM android_metadata";
    return mDb.rawQuery(query, new String[]{myVariable});
}

//Usage
// AnyDBAdatper dba = new AnyDBAdapter(contextObjecT);
// dba.open();
// dba.ExampleCommand("en-CA", "en-GB");
// dba.close();
public void ExampleCommand(String myVariable1, String myVariable2)
{
    String command = "INSERT INTO android_metadata (locale) SELECT ? UNION ALL SELECT  ?";
    mDb.execSQL(command, new String[]{ myVariable1, myVariable2});
}

public void close() {
    mDbHelper.close();
}

private static class DatabaseHelper extends SQLiteOpenHelper {

    Context helperContext;

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

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(TAG, "Upgrading database!!!!!");
        //db.execSQL("");
        onCreate(db);
    }

    public void createDataBase() throws IOException {
        boolean dbExist = checkDataBase();
        if (dbExist) {
        } else {

            //make sure your database has this table already created in it
            //this does not actually work here
            /*
             * db.execSQL("CREATE TABLE IF NOT EXISTS \"android_metadata\" (\"locale\"     TEXT DEFAULT 'en_US')"
             * );
             * db.execSQL("INSERT INTO \"android_metadata\" VALUES ('en_US')"
             * );
             */
            this.getReadableDatabase();
            try {
                copyDataBase();
            } catch (IOException e) {
                throw new Error("Error copying database");
            }
        }
    }

    public SQLiteDatabase getDatabase() {
        String myPath = DB_PATH + DATABASE_NAME;
        return SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READONLY);
    }

    private boolean checkDataBase() {
        SQLiteDatabase checkDB = null;
        try {
            String myPath = DB_PATH + DATABASE_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);
        } catch (SQLiteException e) {
        }
        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 = helperContext.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;
        mDb = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);
    }

    @Override
    public synchronized void close() {

        if (mDb != null)
            mDb.close();

        super.close();

    }
}

}