我跟着this tutorial导入数据库。然后我尝试使用ArrayList读取数据以在listview中显示它们。但我的rawQuery上有nullpointer异常,说它正在调用一个空对象引用。
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;
}
}
Frasa.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;
}
}
activity_list_greetings.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>
ListGreetings.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);
}
}
这是我调用getFrasa
错误的方法吗?或者数据库无法检测到?我确定我已经将数据库文件推送到资源文件夹&amp;包内。对不起,如果我没有正确格式化代码。提前感谢您的帮助。
答案 0 :(得分:0)
问题是您尝试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
正在返回NULL
,因为您的数据库存储在/assets
不在"data/data/hairulhazri.malayforyou/databases/"