Question

这是一个测验应用。有一个问题活动，其中有一个计时器的进度条，一个问题的TextView和四个选项的四个按钮。问题是我无法从/data/data/com.example.mohsinbhat.examsystem/databases/computer.db中读取问题及其答案。另外/data/data/com.example.mohsinbhat.examsystem/databases/computer.db为空。在Text TextView中传递零值，其余的Button文本为空。

这是我的SQLite Helper类，名为computer.java，另一个名为sports.java。这些类的数据库存储在assets文件夹中。

 //computer.java


 package com.example.mohsinbhat.examsystem.MyQuiz;

 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;

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



   public class computer extends SQLiteOpenHelper {

  private static final String Database_path =      
  "/data/data/com.example.mohsinbhat.examsystem/databases/";
  private static final String Database_name = "computer.db";
  //NAME of database stored in Assets folder
  private static final String Table_name = "computer";//name of table
  private static final String uid = "_id";//name of column1
  private static final String Question = "Question";//name of column2
  private static final String OptionA = "OptionA";//name of column3
  private static final String OptionB = "OptionB";//name of column4
  private static final String OptionC = "OptionC";//name of column5
  private static final String OptionD = "OptionD";//name of column6
  private static final String Answer = "Answer";//name of column7
  private static final int version = 1;


  public SQLiteDatabase sqlite;//object of type SQLiteDatabase
  private Context context;//Context object to get context from Question 
                        //Activity

  public computer(Context context) {//constructor
    super(context, Database_name, null, version);
    this.context = context;
   }

  @Override
  public void onCreate(SQLiteDatabase db) {
    //No code because we have already created the database
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    //No code because we have already created the database
  }

  public void createDatabase() {
    createDB();
  }

   private void createDB() {

    boolean dbexist = DBexists();//calling the function to check db exists 
                                  //or not
    if (!dbexist)//if database doesnot exist
    {

        this.getReadableDatabase();//Create an empty file
        copyDBfromResource();//copy the database file information of assets 
                            //folder to newly create file
      }
    }

    private void copyDBfromResource() {

    InputStream is;
    OutputStream os;
    String filePath = Database_path + Database_name;
    try {
        is = context.getAssets().open(Database_name);//reading purpose
        os = new FileOutputStream(filePath);//writing purpose
        byte[] buffer = new byte[1024];
        int length;
        while ((length = is.read(buffer)) > 0) {
            os.write(buffer, 0, length);//writing to file
        }
        os.flush();//flush the outputstream
        is.close();//close the inputstream
        os.close();//close the outputstream

    } catch (IOException e) {
        throw new Error("Problem copying database file:");
      }
    }

   public void openDatabase() throws SQLException//called by onCreate method 
                                                  //of Questions Activity
   {

    String myPath = Database_path + Database_name;
    sqlite = SQLiteDatabase.openDatabase(myPath, null, 
   SQLiteDatabase.OPEN_READWRITE);
   }

   private boolean DBexists()//Check whether the db file exists or not
  {
    SQLiteDatabase db = null;
    try {
        String databasePath = Database_path + Database_name;
        db = SQLiteDatabase.openDatabase(databasePath, null, S 
     QLiteDatabase.OPEN_READWRITE);
        db.setLocale(Locale.getDefault());
        db.setVersion(1);
        db.setLockingEnabled(true);
    } catch (SQLException e) {
        Log.e("Sqlite", "Database not found");
    }
    if (db != null)
        db.close();///close the opened file
    return db != null ? true : false;

    }

    public String readQuestion(int i)//Used to read the data from the Des.db 
                      //file where id is given and we choose id randomly
    {
    String Ans = "";//string that contains the required field  note that Ans 
                //is just a local string not related to Answer or Option...
    Cursor c = sqlite.rawQuery("SELECT " + Question + " FROM " + Table_name 
    + " WHERE "
             + uid + " = " + i + "", null);//cursor to that query

    if (c.moveToFirst())
        Ans = c.getString(0);
    else
        Ans = "";
    c.close();
   return Ans;
   }

    public String readOptionA(int i)//Used to read the data from the Des.db 
                      //file where id is given and we choose id randomly
  {
    String Ans = "";//string that contains the required field  note that Ans 
         //     is just a local string not related to Answer or Option...
    Cursor c = sqlite.rawQuery("SELECT " + OptionA + " FROM " + Table_name + 
        " WHERE "+ uid + " = " + i + "", null);//cursor to that query

    if (c.moveToFirst())
        Ans = c.getString(0);
    else
        Ans = "";
    c.close();
    return Ans;
   }

    public String readOptionB(int i)//Used to read the data from the Des.db 
        //file where id is given and we choose id randomly
  {
    String Ans = "";//string that contains the required field  note that Ans 
   is just a local string not related to Answer or Option...
    Cursor c = sqlite.rawQuery("SELECT " + OptionB + " FROM " + Table_name + 
 " WHERE " + uid + " = " + i + "", null);//cursor to that query

    if (c.moveToFirst())
        Ans = c.getString(0);
    else
        Ans = "";
    c.close();
    return Ans;
    }


  public String readOptionC(int i)//Used to read the data from the Des.db 
  file where id is given and we choose id randomly
  {
    String Ans = "";//string that contains the required field  note that Ans 
    is just a local string not related to Answer or Option...
    Cursor c = sqlite.rawQuery("SELECT " + OptionC + " FROM " + Table_name +        
    " WHERE " + uid + " = " + i + "", null);//cursor to that query

    if (c.moveToFirst())
        Ans = c.getString(0);
    else
        Ans = "";
    c.close();
    return Ans;
    }

       public String readOptionD(int i)//Used to read the data from the        
         //Des.db file where id is given and we choose id randomly
  {
      String Ans = "";//string that contains the required field  note that        
        Ans is just a local string not related to Answer or Option...
    Cursor c = sqlite.rawQuery("SELECT " + OptionD + " FROM " + Table_name +        
      " WHERE "+ uid + " = " + i + "", null);//cursor to that query

    if (c.moveToFirst())
        Ans = c.getString(0);
    else
        Ans = "";
    c.close();
    return Ans;
}

  public String readAnswer(int i)//Used to read the data from the Des.db 
                       //file where id is given and we choose id randomly
   {

    String Ans = "";//string that contains the required field
    Cursor c = sqlite.rawQuery("SELECT " + Answer + " FROM " + Table_name + 
            " WHERE "+ uid + " = " + i + "", null);//cursor to that query

    if (c.moveToFirst())
        Ans = c.getString(0);
    else
        Ans = "";
    c.close();
    return Ans;
    }

这是问题活动的xml布局

      <?xml version="1.0" encoding="utf-8"?>
     <android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MyQuiz.Questions">

    <android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context=".Questions">

    <com.github.lzyzsd.circleprogress.DonutProgress
        android:id="@+id/donut_progress"
        android:layout_width="70dp"
        android:layout_height="70dp"
        android:visibility="invisible"
        android:layout_alignParentEnd="true" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/donut_progress"
        android:orientation="vertical">

        <TextView
            android:id="@+id/Questions"
            android:layout_width="match_parent"
            android:layout_height="140dp"
            android:textAlignment="center"
            android:textColor="#393737"
            android:textSize="28sp" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="120dp"
            android:layout_marginTop="10dp"
            android:orientation="horizontal">


            <Button
                android:id="@+id/OptionA"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:padding="10dp"
                android:onClick="onClick"
                android:foreground="?attr/selectableItemBackground"
                android:textAlignment="center"
                android:visibility="invisible"
                android:textAllCaps="false"
                android:textColor="#ffffff"
                android:textSize="20sp" />
            <Button
                android:id="@+id/OptionB"
                android:layout_width="0dp"
                android:foreground="?attr/selectableItemBackground"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:onClick="onClick"
                android:padding="10dp"
                android:visibility="invisible"
                android:textAlignment="center"
                android:textAllCaps="false"
                android:textColor="#ffffff"
                android:textSize="20sp" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="120dp"
            android:orientation="horizontal">

            <Button
                android:id="@+id/OptionC"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:foreground="?attr/selectableItemBackground"
                android:padding="10dp"
                android:visibility="invisible"
                android:textAlignment="center"
                android:textAllCaps="false"
                android:onClick="onClick"
                android:textColor="#ffffff"
                android:textSize="20sp" />
            <Button
                android:id="@+id/OptionD"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:padding="10dp"
                android:visibility="invisible"
                android:textAlignment="center"
                android:onClick="onClick"
                android:foreground="?attr/selectableItemBackground"
                android:textAllCaps="false"
                android:textColor="#ffffff"
                android:textSize="20sp" />
        </LinearLayout>
    </LinearLayout>

    <Button
        android:id="@+id/play_button"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:layout_below="@+id/donut_progress"
        android:layout_centerHorizontal="true"
        android:layout_gravity="center"
        android:layout_marginTop="13dp"
        android:background="@drawable/custom_option"
        android:foreground="?attr/selectableItemBackground"
        android:onClick="onClick"
        android:text="@string/plays"
        android:textColor="#fff"
        android:textSize="40sp" />
</RelativeLayout>

Answer 1

尝试将数据库从资源文件夹复制到设备存储，然后从那里访问它。下面是将其复制到本地存储的示例代码

    private static final String DATABASE_NAME = "yourdb.sqlite";
    private static final String DB_PATH_SUFFIX = "/databases/"; 

    //Use this function to openDatabase
    //This will copy the database if its not already copied or deleted
    public SQLiteDatabase openDataBase() throws SQLException {
        File dbFile = context.getDatabasePath(DATABASE_NAME);

        if (!dbFile.exists()) {
            try {
                CopyDataBaseFromAsset();
                System.out.println("Copying sucess from Assets folder");
            } catch (IOException e) {
                throw new RuntimeException("Error creating source database", e);
            }
        }

        return SQLiteDatabase.openDatabase(dbFile.getPath(), null, SQLiteDatabase.NO_LOCALIZED_COLLATORS | SQLiteDatabase.CREATE_IF_NECESSARY);
    }

    //This function copies the database to device storage
    public void CopyDataBaseFromAsset() throws IOException {
        InputStream myInput = context.getAssets().open(DATABASE_NAME);

        String outFileName = getDatabasePath();

        File f = new File(context.getApplicationInfo().dataDir + DB_PATH_SUFFIX);
        if (!f.exists())
            f.mkdir();

        OutputStream myOutput = new FileOutputStream(outFileName);

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

        myOutput.flush();
        myOutput.close();
        myInput.close();
    }

    //Get absolute path of database
    private String getDatabasePath() {
        return context.getApplicationInfo().dataDir + DB_PATH_SUFFIX
                + DATABASE_NAME;
    }

无法将资源文件夹中存储的SQLite数据库中的资源/数据复制到/data/data/com.example.mohsinbhat.examsystem/databases/computer.db

1 个答案: