我正在尝试在ListView小部件中显示数据库中的数据。使用SearchView小部件查询数据库。
以下是我的SQlite open helper类的代码：
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 java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class DataBaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static String DB_NAME = "DB.sqlite";
private SQLiteDatabase myDB;
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);
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 = myContext.getDatabasePath(DB_NAME).getPath();
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* 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 = myContext.getDatabasePath(DB_NAME).getPath();
//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 = myContext.getDatabasePath(DB_NAME).getPath();
myDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDB != null)
myDB.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase myDataBase) {
}
@Override
public void onUpgrade(SQLiteDatabase myDataBase, int oldVersion, int newVersion) {
}
public Cursor getC(String animal) {
Cursor c;
c=myDB.rawQuery("SELECT * FROM Table where animal MATCH ?", new String [] {animal});
c.moveToFirst();
return c;
}
}
// 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.
这是我的游标适配器类的代码：
import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CursorAdapter;
import android.widget.TextView;
public class TodoCursorAdapter extends CursorAdapter {
private LayoutInflater mInflater;
public TodoCursorAdapter(Context context, Cursor c, int flags) {
super(context, c, flags);
mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
/* ... */
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
return mInflater.inflate(R.layout.search_item, parent, false);
}
// The bindView method is used to bind all data to a given view
// such as setting the text on a TextView.
@Override
public void bindView(View view, Context context, Cursor cursor) {
TextView content = (TextView) view.findViewById(R.id.résultatAnimal);
content.setText(cursor.getString(2));
}
}
以下是我可搜索活动的代码：
import android.app.ListActivity;
import android.app.SearchManager;
import android.content.Intent;
import android.database.SQLException;
import android.os.Bundle;
import android.widget.ListView;
import java.io.IOException;
public class searchableActivity extends ListActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
DataBaseHelper myDbHelper = new DataBaseHelper(searchableActivity.this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
}catch(SQLException sqle){
throw sqle;
}
super.onCreate(savedInstanceState);
// Get the intent, verify the action and get the query
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
//myDbHelper.getC(query).getString(2);
// Find ListView to populate
ListView AnimalListe = (ListView) findViewById(R.id.list);
// Setup cursor adapter using cursor from last step
TodoCursorAdapter todoAdapter = new TodoCursorAdapter(this, myDbHelper.getC(query), 0);
// Attach cursor adapter to the ListView
AnimalListe.setAdapter(todoAdapter);
}
myDbHelper.close();
}
}
当我在SearchView小部件中启动搜索时，出现错误“NULL POINTER EXCEPTION”并且应用程序崩溃。为什么呢？
答案 0 :(得分：0)
首先请检查是否在Android Monitor中创建数据库。 我认为你的代码是写的，但有时候写下以下代码写在copydatabase中。
private void copyDataBase（）抛出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 = myContext.getDatabasePath(DB_NAME).getPath();
File file=outFileName;
if(!file.isExits)
file.mkdir();
//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();
}