Java Android-导入数据库获取rawquery上的nullpointerexception

我随后导入了数据库。然后我尝试使用ArrayList读取数据，以在listview中显示它们。但我的rawQuery上出现了nullpointer异常，表示它正在调用null对象引用

DB.java

public class DB extends SQLiteOpenHelper {

//The Android's default system path of your application database.
private static String DB_PATH           = "data/data/hairulhazri.malayforyou/databases/";
private static String DB_NAME           = "malayforyou";
private static String TABLE_LOCATION    = "Frasa";

private final Context context;
private SQLiteDatabase db;


// constructor
public DB(Context context) {

    super( context , DB_NAME , null , 1);
    this.context = context;

}


// Creates a empty database on the system and rewrites it with your own database.
public void create() 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 exist to avoid re-copy the data
private boolean checkDataBase(){

    SQLiteDatabase checkDB = null;

    try{
        String path = DB_PATH + DB_NAME;
        checkDB = SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READONLY);

    }catch(SQLiteException e){

        // database don't exist yet.
        e.printStackTrace();

    }

    if(checkDB != null){

        checkDB.close();

    }

    return checkDB != null ? true : false;
}

// copy your assets db to the new system DB
private void copyDataBase() throws IOException{

    //Open your local db as the input stream
    InputStream myInput = context.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();

}

//Open the database
public boolean open() {

    try {
        String myPath = DB_PATH + DB_NAME;
        db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
        return true;

    } catch(SQLException sqle) {
        db = null;
        return false;
    }
}

@Override
public synchronized void close() {

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

    super.close();

}

@Override
public void onCreate(SQLiteDatabase db) {

}

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

}

// PUBLIC METHODS TO ACCESS DB CONTENT
// -----------------------------------------------------------------------------------------------------------------


public ArrayList<Frasa> getFrasa(String situation) {

    //ArrayList of Frasa class objects
    ArrayList<Frasa> arrFrasa = null;
    //String query = "SELECT * FROM Frasa WHERE Situation = " + situation;

    String selectQuery =  "SELECT  " +
            Frasa.KEY_ID + "," +
            Frasa.KEY_PHRASE + "," +
            Frasa.KEY_TRANSLATE + "," +
            Frasa.KEY_PRONOUNCE +
            " FROM " + TABLE_LOCATION + " WHERE situation = " +situation;


    db = SQLiteDatabase.openDatabase( DB_PATH + DB_NAME , null, SQLiteDatabase.OPEN_READWRITE);
    Cursor curFrasa = db.rawQuery(selectQuery, null);

    if (curFrasa != null && curFrasa.moveToFirst()) {
        arrFrasa = new ArrayList<Frasa>();
        while (curFrasa.isAfterLast() == false) {
            //Frasa is a class with list of fields
            Frasa fra = new Frasa();
            fra.setId(curFrasa.getInt(curFrasa.getColumnIndex(Frasa.KEY_ID)));
            fra.setPhrase(curFrasa.getString(curFrasa.getColumnIndex(Frasa.KEY_PHRASE)));
            fra.setTranslate(curFrasa.getString(curFrasa.getColumnIndex(Frasa.KEY_TRANSLATE)));
            fra.setPronounce(curFrasa.getString(curFrasa.getColumnIndex(Frasa.KEY_PRONOUNCE)));
            arrFrasa.add(fra);
            curFrasa.moveToNext();
        }
    }
    curFrasa.close();
    db.close();
    return arrFrasa;
  }
}

java数据库表和列

public class Frasa {



// Labels Table Columns names
public static final String KEY_ID = "id";
public static final String KEY_PHRASE = "phrase";
public static final String KEY_TRANSLATE = "translate";
public static final String KEY_PRONOUNCE = "pronounce";


// property help us to keep data
public int id;
public String situation;
public String phrase;
public String translate;
public String pronounce;


public Frasa() {
}

public Frasa(int id, String situation, String phrase, String translate, String pronounce) {
    this.id = id;
    this.situation = situation;
    this.phrase = phrase;
    this.translate = translate;
    this.pronounce = pronounce;
}


public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getPhrase() {
    return phrase;
}

public void setPhrase(String phrase) {
    this.phrase = phrase;
}

public String getTranslate() {
    return translate;
}

public void setTranslate(String translate) {
    this.translate = translate;
}

public String getPronounce() {
    return pronounce;
}

public void setPronounce(String pronounce) {
    this.pronounce = pronounce;
}
}



public class GreetingAdapter extends ArrayAdapter<Frasa> {
Context context;
int layoutResourceId;
ArrayList<Frasa> data = new ArrayList<Frasa>();

public GreetingAdapter(Context context, int layoutResourceId, ArrayList<Frasa> data)
{
    super(context, layoutResourceId, data);
    this.layoutResourceId = layoutResourceId;
    this.context = context;
    this.data = data;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View row = convertView;
    UserHolder holder = null;

    if (row == null) {
        LayoutInflater inflater = ((Activity) context).getLayoutInflater();
        row = inflater.inflate(layoutResourceId, parent, false);
        holder = new UserHolder();
        holder.textPhrase = (TextView) row.findViewById(R.id.textViewPhrase);
        holder.textTranslate = (TextView) row.findViewById(R.id.textViewTranslate);
        holder.btnSpeak = (Button) row.findViewById(R.id.buttonSpeak);
        holder.btnRecord = (Button) row.findViewById(R.id.buttonRecord);
        holder.btnPlay = (Button) row.findViewById(R.id.buttonPlay);
        row.setTag(holder);
    } else {
        holder = (UserHolder) row.getTag();
    }
    Frasa frasa = data.get(position);
    holder.textPhrase.setText(frasa.getPhrase());
    holder.textTranslate.setText(frasa.getTranslate());
    holder.btnSpeak.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Log.i("Edit Button Clicked", "**********");
            Toast.makeText(context, "Speak button Clicked",
                    Toast.LENGTH_LONG).show();
        }
    });
    holder.btnRecord.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Log.i("Delete Button Clicked", "**********");
            Toast.makeText(context, "Delete button Clicked",
                    Toast.LENGTH_LONG).show();
        }
    });
    holder.btnPlay.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Log.i("Play Button Clicked", "**********");
            Toast.makeText(context, "Playing recorded audio",
                    Toast.LENGTH_LONG).show();
        }
    });
    return row;

}

static class UserHolder {
    TextView textPhrase;
    TextView textTranslate;
    Button btnSpeak;
    Button btnRecord;
    Button btnPlay;
}
}

活动\u列表\u问候语.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:layout_width="match_parent"

android:layout_height="match_parent">

<TextView
    android:id="@+id/txt_header"
    android:layout_width="match_parent"
    android:layout_height="48dp"
    android:layout_centerHorizontal="true"
    android:gravity="center"
    android:text="Greetings"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:textColor="@android:color/black" />

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/listGreetings"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true"
    android:layout_below="@+id/txt_header" />

list_item_greet.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
    android:id="@+id/textViewPhrase"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Phrase"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:layout_above="@+id/buttonRecord"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />


<Button
    android:id="@+id/buttonSpeak"
    android:layout_width="80dp"
    android:layout_height="40dp"
    android:layout_alignParentRight="true"
    android:layout_alignParentTop="true"
    android:background="#FFFFFF"
    android:focusable="false"
    android:focusableInTouchMode="false"
    android:text="Speak"
    android:textColor="#0099CC" />

<Button
    android:id="@+id/buttonRecord"
    android:layout_width="80dp"
    android:layout_height="40dp"
    android:layout_alignParentRight="true"
    android:layout_below="@+id/buttonSpeak"
    android:layout_marginTop="3dp"
    android:background="#FFFFFF"
    android:focusable="false"
    android:focusableInTouchMode="false"
    android:text="Record"
    android:textColor="#0099CC" />

<Button
    android:id="@+id/buttonPlay"
    android:layout_width="80dp"
    android:layout_height="40dp"
    android:layout_alignParentRight="true"
    android:layout_below="@+id/buttonRecord"
    android:layout_marginTop="3dp"
    android:background="#FFFFFF"
    android:focusable="false"
    android:focusableInTouchMode="false"
    android:text="Play"
    android:textColor="#0099CC" />

<TextView
    android:id="@+id/textViewTranslate"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Translate"
    android:textSize="20sp"
    android:textColor="@color/background_material_dark"
    android:layout_below="@+id/buttonRecord"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />

</RelativeLayout>

java

public class ListGreetings extends ActionBarActivity {

TextView txtPhrase, txtTranslate;
Button speakButton;
MediaPlayer pronounce;

ListView userList;
GreetingAdapter greetAdapter;

//ArrayList<Frasa> frasaArray = new ArrayList<Frasa>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_greetings);


    DB db = new DB(this);
    db.open();


    //get Frasa data
        ArrayList<Frasa> frasaArray = db.getFrasa("Greetings");


        /**
         * set item into adapter
         */
        greetAdapter = new GreetingAdapter(ListGreetings.this, R.layout.list_item_greet, frasaArray);
        userList = (ListView) findViewById(R.id.listGreetings);
        userList.setItemsCanFocus(false);
        userList.setAdapter(greetAdapter);

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_list_greetings, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
  }
}

---

这是我给getFrasa打错电话的方式吗？或者无法检测到数据库？我确信我已经将数据库文件推送到包中的两个资产文件夹中。抱歉，如果我没有正确格式化代码。提前感谢您的帮助。

问题是您试图从其他位置打开数据库

private static String DB_PATH = "data/data/hairulhazri.malayforyou/databases/";
private static String DB_NAME = "malayforyou";
...
...
db = SQLiteDatabase.openDatabase( DB_PATH + DB_NAME , null, SQLiteDatabase.OPEN_READWRITE); 

---

db返回NULL，因为您的数据库存储在/assets文件夹中，而不是data/data/hairulhazri.malayforyou/databases/

Wellcome to StackOverflow！显示LogCat中显示的错误消息非常有价值，因此我们可以很容易地找到问题：哦，对不起。这是错误消息。。。。。。。。原因：java.lang.NullPointerException:尝试调用虚拟方法“android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQueryjava.lang.String，java.lang.String[]'hairulhazri.malayforyou.database.DB.getFrasaDB.java:194在hairulhazri.malayforyou.ListGreetings.onCreateListGreetings.java:42Inside ListGreetings.java oncreate:ArrayList frasaArray=DB.getFrasaGreetings；你的数据库的全名是什么？malayforyou.db？？？只是“malayforyou”。文件类型为“File”，但可以在SQLite浏览器中打开。我将数据库存储在assets文件夹中，并将数据库推送到DDMS中的包中，就像在教程中一样。很抱歉@Elenasys，但我不太明白。到底是什么问题？你说路径是错误的，但我这么做是因为我遵循了教程。这让我很困惑。