【问题标题】:Unable to use external database in Android app无法在 Android 应用程序中使用外部数据库
【发布时间】:2015-12-24 04:58:26
【问题描述】:

我想在 MySQL 中使用我的外部数据库。我有一个存档数据库databse.db.zip,并将其复制到我的Android Java 项目的assets 文件夹中。最后我创建了一个打开数据库的类:

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteQueryBuilder;
import com.readystatesoftware.sqliteasset.SQLiteAssetHelper;

public class databaseOpen extends SQLiteAssetHelper {

private static final String DATABASE_NAME = "parole.db";
private static final int DATABASE_VERSION = 1;

public databaseOpen(Context context) {

    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public String risposta(String parolain ){
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String[] selectionArgs = {"ciao"};
    Cursor c =db.query("prima", null, null,selectionArgs, null, null,   null);
    c.moveToFirst();

    return c.getString(0);
}
}

我已经在我的main 中回收了它:

private databaseOpen db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    db = new databaseOpen(this);
    Toast toast=Toast.makeText(this, db.risposta("ciao"), Toast.LENGTH_LONG);
}

但它不起作用。这是我得到的输出:

09-26 15:20:23.761    1099-1099/? I/SQLiteAssetHelper successfully opened database parole.db
09-26 15:20:23.764    1099-1099/? E/SQLiteLog (1) no such table: prima
09-26 15:20:23.783    1099-1099/? D/AndroidRuntime Shutting down VM
09-26 15:20:23.801    1099-1099/? E/AndroidRuntime FATAL EXCEPTION: main
    Process: com.example.roby.jarvis, PID: 1099
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.roby.jarvis/com.example.roby.jarvis.Home}: android.database.sqlite.SQLiteException: no such table: prima (code 1): , while compiling: SELECT * FROM prima

【问题讨论】:

  • Logcat 告诉你... 没有这样的表:prima

标签: java android mysql database sqlite


【解决方案1】:

我想在 mysql 中使用我的外部数据库,我已经压缩了这个 (databse.db.zip) 并将它复制到我的 java 项目的 assents 文件夹中

为了记录, 要么您使用了错误的术语,要么感到困惑。 Android 和您帖子中的代码可与 SQLite 一起使用。 它不能与 MySQL 一起使用。

当某些事情不起作用时, 阅读错误信息, 这通常可以解释问题,例如:

09-26 15:20:23.764 1099-1099/? E/SQLiteLog: (1) no such table: prima

文件中不存在名为“prima”的表。

调试的下一步是检查 PC 上文件的内容, 使用sqlite3 命令行工具或类似工具, 并查看它有哪些表(.schema 命令)。

【讨论】:

    【解决方案2】:

    首先:您没有将Database 文件从资产文件复制到您的设备,这显然会导致no such table found

    试试这个代码,它对我有用。 (我还评论了不同的部分以供您理解)

    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.SQLiteException;
    import android.database.sqlite.SQLiteOpenHelper;
    import android.os.Build;
    import android.util.Log;
    
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    
    /**
    * Created by HP-HP on 23-07-2015.
    */
    public class DataBaseHelper extends SQLiteOpenHelper {
    
    //The Android's default system path of your application database.
    private static String DB_PATH ;
    
    private static String DB_NAME = "profanityv2";
    
    private SQLiteDatabase myDataBase;
    
    private final Context myContext;
    
    /**
     * 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, DB_NAME, null, 1);
    
        if(android.os.Build.VERSION.SDK_INT >= 4.2){
            DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
        } else {
            DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
        }
    
        this.myContext = context;
    }
    
    /**
     * Creates a empty database on the system and rewrites it with your own database.
     * */
    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");
    
            }
        }
    
    }
    
    /**
     * 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.
            try {
                myContext.deleteDatabase("profanity");
            } catch (Exception e1) {
                e1.printStackTrace();
            }
        }
    
        if(checkDB != null){
    
            checkDB.close();
    
        }
    
        return checkDB != null;
    }
    
    /**
     * 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.NO_LOCALIZED_COLLATORS|SQLiteDatabase.CREATE_IF_NECESSARY );
    
    }
    
    @Override
    public synchronized void close() {
    
        if(myDataBase != null)
            myDataBase.close();
    
        super.close();
    
    }
    
    public Cursor getData() {
        Cursor c = null;
        try {
            c = myDataBase.rawQuery("SELECT * FROM profanity_table", null);
        } catch (Exception e) {
            e.printStackTrace();
        }
        // Note: Master is the one table in External db. Here we trying to access the records of table from external db.
        return c;
    }
    
    
    @Override
    public void onCreate(SQLiteDatabase db) {
    
    }
    
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    
    }
    
    // Add your public helper methods to access and get content from the database.
    // You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
    // to you to create adapters for your views.
    
    }
    

    用法:

    DataBaseHelper dataBaseHelper = new DataBaseHelper(this);
    
        try {
            dataBaseHelper.createDataBase();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    
        try {
    
            dataBaseHelper.openDataBase();
    
        }catch(SQLException sqle){
    
            throw sqle;
    
        }
    
        Cursor c = dataBaseHelper.getData();
    
        if(c!=null) {
            /* your cursor code */
            c.close();
        }
    
    
        dataBaseHelper.close();
    

    *注意:某些设备可能无法将数据库复制到设备。(已知设备:OnePlus)

    别忘了添加这个权限

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    在您的清单中。

    编辑 1: OnePlus 能够将数据库复制到 /data/data/<package-name>/databases/<filename>.db,但它不允许访问该数据,我对此一无所知。

    【讨论】:

    • 但是我在项目中复制我的数据库
    • 我已经使用了你的代码,但是 android 找不到表,但应用程序现在没有崩溃,我尝试使用 sqlitebrowser 搜索表并找到表和值
    • 您有存储数据库的路径吗?通过记录路径或通过 sqlitebrowser 获取它。如果您尝试在上述代码中手动编辑 DB_PATH。
    • 我已将数据库复制到我的电脑中手机的文件夹 app/databases 中,并使用 sqlitebrowser 打开它
    • @swalkner 请看Edit1
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