Android 从sqlite检索记录

对不起，我的英语不好。
我是Android Studio的新手

我有一个外部数据库。具有列id、text1、text2…text6 不知何故，我在youtube教程之后成功地将该数据库添加到了我的应用程序中。那很好

---

我将其添加到资产，并在mainActivity中复制到data/data/mypackage/databases。我在emulator文件资源管理器中进行了检查

现在我需要从那个数据库中获取数据，但我不知道该怎么做

id列为自动递增整数。 我的应用程序中有一个数组，其中包含x个在某个范围内随机生成的整数。 现在，我想在数据库中查询数组中的第一个整数，并用结果更新活动中的TextView。在用户点击一个按钮后，我需要从数组中发送下一个整数的另一个查询，以此类推

我不知道热打开数据库，发送查询。。。我尝试了很多教程，在互联网上搜索解决方案，但没有一个奏效。现在我只是糊涂了

我有SQL方面的经验。这不应该是个问题。在PHP和MySql中，只需几行代码即可完成。 谁能帮我解决这个问题

这是我的助手

package com.examle.mydbapp;

import android.annotation.SuppressLint;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.SQLException;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.util.Log;

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

class dbHelper extends SQLiteOpenHelper {


    private static final String DATABASE_PATH = "/data/data/com.example.mydbapp/databases/";
    private static final String DATABASE_NAME = "quotes.db";
    private  static final int SCHEMA_VERSION = 1;

    public SQLiteDatabase dbSglite;

    private final Context myContext;

    public dbHelper(Context context) {
        super(context, DATABASE_NAME, null, SCHEMA_VERSION);
        this.myContext=context;
       }

       @Override
    public void onCreate(SQLiteDatabase db){

       }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public void createDatabase(){
        createDB();
    }

    private void createDB(){

        boolean dbExist = DBExists();

        if(!dbExist){
            this.getReadableDatabase();
            copyDBFromResource();

        }


    }

    private boolean DBExists(){

        SQLiteDatabase db = null;

        try {
            String databasePath = DATABASE_PATH+DATABASE_NAME;
            db = SQLiteDatabase.openDatabase(databasePath,null, SQLiteDatabase.OPEN_READWRITE);
            db.setLocale(Locale.getDefault());
            db.setLockingEnabled(true);
            db.setVersion(1);
        } catch (SQLiteException e) {

            Log.e("SqlHelper", "database not found");
        }

        if (db != null) {
            db.close();
        }
        return db != null ? true : false;

    }

    private void copyDBFromResource() {
        InputStream inputStream = null;
        OutputStream outputStream = null;
        String dbFilePath=DATABASE_PATH+DATABASE_NAME;

        try {
            inputStream = myContext.getAssets().open(DATABASE_NAME);
            outputStream = new FileOutputStream(dbFilePath);

            byte[] buffer = new byte[1024];
            int length;
            while ((length=inputStream.read(buffer))>0){
                outputStream.write(buffer, 0, length);
            }

            outputStream.flush();
            outputStream.close();
            inputStream.close();

        } catch (IOException e) {

            throw new Error("Problem copying database.");
        }

    }

    public void openDataBase() throws SQLException {

        String myPath = DATABASE_PATH + DATABASE_NAME;
        dbSglite = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);

    }

}

---

简言之，假设您希望访问活动中的数据，那么

您可以a）创建databasehelper的实例b）调用databasehelper的

createDatabase

方法，然后c）通过调用databasehelper的

GetWriteableDatabase

检索SQLiteDatabase实例方法

（您可能已经完成了a和b）

e、 g:-

    dbhlpr = new dbHelper(this);
    // Create the Database if need be
    dbhlpr.createDatabase();
    // An example of getting a instance outside of the helper
    SQLiteDatabase db = dbhlpr.getWritableDatabase();

您还可以使用

SQLiteDatabase db=dbhlpr.dbSglite

而不是

SQLiteDatabase db=dbhlpr.getWritableDatabase（）；

• 其中，在上述

  dbhlpr

  中，是使用

  dbHelper dbhlpr定义的类变量

然后可以通过创建游标从表中检索数据。在以下示例中（前面是前面的示例代码，并假设该表名为quotes），您可以按照以下示例的思路进行操作：-

EX 1（来自sqlite_master） 注意事项：-

• 空游标是有效游标a；查询不会返回空游标
• 使用列偏移量，例如

  csr3.getLong（0）

  可能会有问题，因此替代方法更灵活

  csr3.getLong（csr3.getColumnIndex（“id”）

• 当从

  query

  方法返回光标时，它的位置在第一行（-1）之前。要访问数据，必须使用

  move？？？

  方法，例如

  csr3.moveToFirst（）

  。

  移动？？？

  方法在移动时返回true，在无法移动时返回false

测试 上面的代码已经使用与问题中提供的DatabaseHelper非常相同的DatabaseHelper进行了测试

该数据库是在应用程序外部创建的，其中一个表添加了名为quotes的数据，其中两行数据按照以下方式添加：-

在没有现有数据库的情况下运行测试1的输出：- 注意！捕获并绕过/处理了文件错误（即，仅仅因为数据库不存在）

测试2的输出-数据库存在：- 用于上述操作的DatabaseHelper 由于packagename是在Databasehelper中硬编码的，因此必须进行更改。因此，与其对包进行硬编码，不如通过

context.getDatabasePath（database_NAME）.getParent（）获取数据库路径（不带databasename和separatinf/）。为了防止数据库文件夹/目录不存在，更改的帮助程序将使用
File databasesdir=new File（myContext.getDatabasePath（DATABASE_NAME.getParent（））创建目录；
databasesdir.mkdirs（）

完整助手是：-

class dbHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "quotes.db";
    private  static final int SCHEMA_VERSION = 1;

    public SQLiteDatabase dbSglite;
    private String mDBPAth;

    private final Context myContext;

    public dbHelper(Context context) {
        super(context, DATABASE_NAME, null, SCHEMA_VERSION);
        this.myContext=context;
        this.mDBPAth = context.getDatabasePath(DATABASE_NAME).getParent();
    }

    @Override
    public void onCreate(SQLiteDatabase db){
        Log.d("ONCREATE","OnCreate Method Called.");

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public void createDatabase(){
        createDB();
    }

    private void createDB(){

        boolean dbExist = DBExists();

        if(!dbExist){
            copyDBFromResource();

        }
        dbSglite = getWritableDatabase();
    }

    private boolean DBExists(){

        SQLiteDatabase db = null;

        try {
            String databasePath = myContext.getDatabasePath(DATABASE_NAME).getPath();
            db = SQLiteDatabase.openDatabase(databasePath,null, SQLiteDatabase.OPEN_READWRITE);
            db.setLocale(Locale.getDefault());
            db.setLockingEnabled(true);
            db.setVersion(1);
        } catch (SQLiteException e) {

            Log.e("SqlHelper", "database not found");
        }

        if (db != null) {
            db.close();
        }
        return db != null;
    }

    private void copyDBFromResource() {
        InputStream inputStream = null;
        OutputStream outputStream = null;

        try {
            inputStream = myContext.getAssets().open(DATABASE_NAME);
            File databasesdir =  new File(myContext.getDatabasePath(DATABASE_NAME).getParent());
            databasesdir.mkdirs();
            outputStream = new FileOutputStream(mDBPAth+"/"+DATABASE_NAME);
            byte[] buffer = new byte[1024];
            int length;
            while ((length=inputStream.read(buffer))>0){
                outputStream.write(buffer, 0, length);
            }

            outputStream.flush();
            outputStream.close();
            inputStream.close();

        } catch (IOException e) {
            e.printStackTrace();
            throw new Error("Problem copying database.");
        }
    }

    public void openDataBase() throws SQLException {

        String myPath = myContext.getDatabasePath(DATABASE_NAME).getPath();
        dbSglite = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);
    }
}

数据库在哪里？您是否刚刚将其添加为资产，或者它是以某种方式存在于data/data/your_package/databases中，还是存在于其他地方。我将其添加到资产，并在mainActivity中复制到data/data/mypackage/databases中。我在emulator文件资源管理器中检查了它。的副本。询问前请仔细搜索。
    // Get and process data from the quotes table
    Cursor csr2 = db.query("quotes",null,null,null,null,null,null);
    while (csr2.moveToNext()) {
        String tblinfo = "Row " + csr2.getPosition();
        for (int i=0; i < csr2.getColumnCount(); i++) {
            tblinfo = tblinfo + " Column = " + csr2.getColumnName(i) + " Value = " + csr2.getString(i);
        }
        Log.d("CURSOR 2 INFO",tblinfo);
    }
    csr2.close();

    // Get and processs data for a specific row according to id
    Cursor csr3 = db.query("quotes",null,"id=?",new String[]{"1"},null,null,null);
    if (csr3.moveToFirst()) {
        Log.d("CURSOR 3 INFO",
                " ID is" + csr3.getLong(0) +
                        " ID is " + csr3.getLong(csr3.getColumnIndex("id")) +
                        " TEXT1 is " + csr3.getString(csr3.getColumnIndex("text1"))
                // ..... etc
        );
    }
    csr3.close();

-15 11:30:20.066 8446-8446/? E/SQLiteLog: (14) cannot open file at line 30046 of [9491ba7d73]
11-15 11:30:20.066 8446-8446/? E/SQLiteLog: (14) os_unix.c:30046: (2) open(/data/data/mjt.usingrecyclerviews/databases/quotes.db) - 
11-15 11:30:20.066 8446-8446/? E/SQLiteDatabase: Failed to open database '/data/data/mjt.usingrecyclerviews/databases/quotes.db'.
android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (code 14): Could not open database
    at android.database.sqlite.SQLiteConnection.nativeOpen(Native Method)
    at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:209)
    at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:193)
    at android.database.sqlite.SQLiteConnectionPool.openConnectionLocked(SQLiteConnectionPool.java:463)
    at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:185)
    at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:177)
    at android.database.sqlite.SQLiteDatabase.openInner(SQLiteDatabase.java:806)
    at android.database.sqlite.SQLiteDatabase.open(SQLiteDatabase.java:791)
    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:694)
    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:669)
    at mjt.usingrecyclerviews.dbHelper.DBExists(dbHelper.java:68)
    at mjt.usingrecyclerviews.dbHelper.createDB(dbHelper.java:54)
    at mjt.usingrecyclerviews.dbHelper.createDatabase(dbHelper.java:49)
    at mjt.usingrecyclerviews.MainActivity.onCreate(MainActivity.java:27)
    at android.app.Activity.performCreate(Activity.java:5990)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
    at android.app.ActivityThread.access$800(ActivityThread.java:151)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:135)
    at android.app.ActivityThread.main(ActivityThread.java:5254)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
11-15 11:30:20.066 8446-8446/? E/SqlHelper: database not found
11-15 11:30:20.093 8446-8446/? D/ONCREATE: OnCreate Method Called.
11-15 11:30:20.096 8446-8446/? D/SQLITEINFO: Row 0 Column = type Value = table Column = name Value = quotes Column = tbl_name Value = quotes Column = rootpage Value = 2 Column = sql Value = CREATE TABLE quotes (id INTEGER PRIMARY KEY, text1 TEXT,  text2 TEXT, text3 TEXT, text4 TEXT, text5 TEXT)
11-15 11:30:20.096 8446-8446/? D/SQLITEINFO: Row 1 Column = type Value = table Column = name Value = android_metadata Column = tbl_name Value = android_metadata Column = rootpage Value = 3 Column = sql Value = CREATE TABLE android_metadata (locale TEXT)
11-15 11:30:20.096 8446-8446/? D/CURSOR 2 INFO: Row 0 Column = id Value = 1 Column = text1 Value = Some quote Column = text2 Value = Another quote Column = text3 Value = Yet another quote Column = text4 Value = This is a quote Column = text5 Value = Too many quotes
11-15 11:30:20.096 8446-8446/? D/CURSOR 2 INFO: Row 1 Column = id Value = 2 Column = text1 Value = Seccond quote Column = text2 Value = Third Quote Column = text3 Value = Fourth Quote Column = text4 Value = Fifth Quote Column = text5 Value = Sixth Quote
11-15 11:30:20.096 8446-8446/? D/CURSOR 3 INFO:  ID is1 ID is 1 TEXT1 is Some quote

11-15 11:33:17.111 8511-8511/mjt.usingrecyclerviews D/SQLITEINFO: Row 0 Column = type Value = table Column = name Value = quotes Column = tbl_name Value = quotes Column = rootpage Value = 2 Column = sql Value = CREATE TABLE quotes (id INTEGER PRIMARY KEY, text1 TEXT,  text2 TEXT, text3 TEXT, text4 TEXT, text5 TEXT)
11-15 11:33:17.111 8511-8511/mjt.usingrecyclerviews D/SQLITEINFO: Row 1 Column = type Value = table Column = name Value = android_metadata Column = tbl_name Value = android_metadata Column = rootpage Value = 3 Column = sql Value = CREATE TABLE android_metadata (locale TEXT)
11-15 11:33:17.111 8511-8511/mjt.usingrecyclerviews D/CURSOR 2 INFO: Row 0 Column = id Value = 1 Column = text1 Value = Some quote Column = text2 Value = Another quote Column = text3 Value = Yet another quote Column = text4 Value = This is a quote Column = text5 Value = Too many quotes
11-15 11:33:17.112 8511-8511/mjt.usingrecyclerviews D/CURSOR 2 INFO: Row 1 Column = id Value = 2 Column = text1 Value = Seccond quote Column = text2 Value = Third Quote Column = text3 Value = Fourth Quote Column = text4 Value = Fifth Quote Column = text5 Value = Sixth Quote
11-15 11:33:17.113 8511-8511/mjt.usingrecyclerviews D/CURSOR 3 INFO:  ID is1 ID is 1 TEXT1 is Some quote

class dbHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "quotes.db";
    private  static final int SCHEMA_VERSION = 1;

    public SQLiteDatabase dbSglite;
    private String mDBPAth;

    private final Context myContext;

    public dbHelper(Context context) {
        super(context, DATABASE_NAME, null, SCHEMA_VERSION);
        this.myContext=context;
        this.mDBPAth = context.getDatabasePath(DATABASE_NAME).getParent();
    }

    @Override
    public void onCreate(SQLiteDatabase db){
        Log.d("ONCREATE","OnCreate Method Called.");

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public void createDatabase(){
        createDB();
    }

    private void createDB(){

        boolean dbExist = DBExists();

        if(!dbExist){
            copyDBFromResource();

        }
        dbSglite = getWritableDatabase();
    }

    private boolean DBExists(){

        SQLiteDatabase db = null;

        try {
            String databasePath = myContext.getDatabasePath(DATABASE_NAME).getPath();
            db = SQLiteDatabase.openDatabase(databasePath,null, SQLiteDatabase.OPEN_READWRITE);
            db.setLocale(Locale.getDefault());
            db.setLockingEnabled(true);
            db.setVersion(1);
        } catch (SQLiteException e) {

            Log.e("SqlHelper", "database not found");
        }

        if (db != null) {
            db.close();
        }
        return db != null;
    }

    private void copyDBFromResource() {
        InputStream inputStream = null;
        OutputStream outputStream = null;

        try {
            inputStream = myContext.getAssets().open(DATABASE_NAME);
            File databasesdir =  new File(myContext.getDatabasePath(DATABASE_NAME).getParent());
            databasesdir.mkdirs();
            outputStream = new FileOutputStream(mDBPAth+"/"+DATABASE_NAME);
            byte[] buffer = new byte[1024];
            int length;
            while ((length=inputStream.read(buffer))>0){
                outputStream.write(buffer, 0, length);
            }

            outputStream.flush();
            outputStream.close();
            inputStream.close();

        } catch (IOException e) {
            e.printStackTrace();
            throw new Error("Problem copying database.");
        }
    }

    public void openDataBase() throws SQLException {

        String myPath = myContext.getDatabasePath(DATABASE_NAME).getPath();
        dbSglite = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);
    }
}