我已经将我的 sqlite 数据库文件放在“assets”文件夹中并且我编写了一个 DataManager 类来从数据库中获取数据，但是我遇到了运行时错误..我使用调试工具来查看我在 CreateDataBase() 出现错误.. 请帮我解决这个问题
这是我的 Datamanager 类。我正在为 Android 预创建数据库，但我收到文件未找到异常请帮助我..我在下面显示了我的 Logcat。
(数据管理类)
package com.example.applicationdatabase;
import android.content.ContentValues;
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 DataBaseManager extends SQLiteOpenHelper {
// The Android's default system path of your application database.
//data/data/ and /databases remain the same always. The one that must be changed is com.example which represents
//the MAIN package of your project
private static String DB_PATH = "/data/data/com.example.applicationdatabase/databases";
//the name of your database
private static String DB_NAME = "database";
private static SQLiteDatabase mDataBase;
private static DataBaseManager sInstance = null;
// database version
private static final int DATABASE_VERSION = 1;
/**
* Constructor Takes and keeps a reference of the passed context in order to
* access to the application assets and resources.
*/
private DataBaseManager() {
super(ApplicationContextProvider.getContext(), DB_NAME, null, DATABASE_VERSION);
try {
createDataBase();
openDataBase();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* Singleton for DataBase
*
* @return singleton instance
*/
public static DataBaseManager instance() {
if (sInstance == null) {
sInstance = new DataBaseManager();
}
return sInstance;
}
/**
* Creates a empty database on the system and rewrites it with your own
* database.
*
* @throws java.io.IOException io exception
*/
private void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
// do nothing - database already exist
} else {
// By calling this method an 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 = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
// database doesn't exist yet.
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null;
}
/**
* 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.
*
* @throws java.io.IOException io exception
*/
public void copyDataBase() throws IOException {
// Open your local db as the input stream
InputStream myInput =ApplicationContextProvider.getContext().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();
}
private void openDataBase() throws SQLException {
// Open the database
String myPath = DB_PATH + DB_NAME;
mDataBase = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
}
/**
* Select method
*
* @param query select query
* @return - Cursor with the results
* @throws android.database.SQLException sql exception
*/
public Cursor select(String query) throws SQLException {
return mDataBase.rawQuery(query, null);
}
/**
* Insert method
*
* @param table - name of the table
* @param values values to insert
* @throws android.database.SQLException sql exception
*/
public void insert(String table, ContentValues values) throws SQLException {
mDataBase.insert(table, null, values);
}
/**
* Delete method
*
* @param table - table name
* @param where WHERE clause, if pass null, all the rows will be deleted
* @throws android.database.SQLException sql exception
*/
public void delete(String table, String where) throws SQLException {
mDataBase.delete(table, where, null);
}
/**
* Update method
*
* @param table - table name
* @param values - values to update
* @param where - WHERE clause, if pass null, all rows will be updated
*/
public void update(String table, ContentValues values, String where) {
mDataBase.update(table, values, where, null);
}
/**
* Let you make a raw query
*
* @param command - the sql comand you want to run
*/
public void sqlCommand(String command) {
mDataBase.execSQL(command);
}
@Override
public synchronized void close() {
if (mDataBase != null)
mDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
日志:
11-30 16:02:18.908: E/SQLiteLog(968): (14) cannot open file at line 30176 of [00bb9c9ce4]
11-30 16:02:18.938: E/SQLiteLog(968): (14) os_unix.c:30176: (2) open(/data/data/com.example.applicationdatabase/databasesdatabase) -
11-30 16:02:18.948: E/SQLiteDatabase(968): Failed to open database '/data/data/com.example.applicationdatabase/databasesdatabase'.
11-30 16:02:18.948: E/SQLiteDatabase(968): android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (code 14): Could not open database
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteConnection.nativeOpen(Native Method)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:209)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:193)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteConnectionPool.openConnectionLocked(SQLiteConnectionPool.java:463)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:185)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:177)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteDatabase.openInner(SQLiteDatabase.java:804)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteDatabase.open(SQLiteDatabase.java:789)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:694)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:669)
11-30 16:02:18.948: E/SQLiteDatabase(968): at com.example.applicationdatabase.DataBaseManager.checkDataBase(DataBaseManager.java:102)
11-30 16:02:18.948: E/SQLiteDatabase(968): at com.example.applicationdatabase.DataBaseManager.createDataBase(DataBaseManager.java:69)
11-30 16:02:18.948: E/SQLiteDatabase(968): at com.example.applicationdatabase.DataBaseManager.<init>(DataBaseManager.java:39)
11-30 16:02:18.948: E/SQLiteDatabase(968): at com.example.applicationdatabase.DataBaseManager.instance(DataBaseManager.java:55)
11-30 16:02:18.948: E/SQLiteDatabase(968): at com.example.applicationdatabase.DBActivity.onCreate(DBActivity.java:35)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.app.Activity.performCreate(Activity.java:5104)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.os.Handler.dispatchMessage(Handler.java:99)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.os.Looper.loop(Looper.java:137)
11-30 16:02:18.948: E/SQLiteDatabase(968): at android.app.ActivityThread.main(ActivityThread.java:5039)
11-30 16:02:18.948: E/SQLiteDatabase(968): at java.lang.reflect.Method.invokeNative(Native Method)
11-30 16:02:18.948: E/SQLiteDatabase(968): at java.lang.reflect.Method.invoke(Method.java:511)
11-30 16:02:18.948: E/SQLiteDatabase(968): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
11-30 16:02:18.948: E/SQLiteDatabase(968): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
11-30 16:02:18.948: E/SQLiteDatabase(968): at dalvik.system.NativeStart.main(Native Method)
11-30 16:02:19.008: E/AndroidRuntime(968): FATAL EXCEPTION: main
11-30 16:02:19.008: E/AndroidRuntime(968): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.applicationdatabase/com.example.applicationdatabase.DBActivity}: java.lang.NullPointerException
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.os.Handler.dispatchMessage(Handler.java:99)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.os.Looper.loop(Looper.java:137)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.ActivityThread.main(ActivityThread.java:5039)
11-30 16:02:19.008: E/AndroidRuntime(968): at java.lang.reflect.Method.invokeNative(Native Method)
11-30 16:02:19.008: E/AndroidRuntime(968): at java.lang.reflect.Method.invoke(Method.java:511)
11-30 16:02:19.008: E/AndroidRuntime(968): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
11-30 16:02:19.008: E/AndroidRuntime(968): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
11-30 16:02:19.008: E/AndroidRuntime(968): at dalvik.system.NativeStart.main(Native Method)
11-30 16:02:19.008: E/AndroidRuntime(968): Caused by: java.lang.NullPointerException
11-30 16:02:19.008: E/AndroidRuntime(968): at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:188)
11-30 16:02:19.008: E/AndroidRuntime(968): at com.example.applicationdatabase.DataBaseManager.createDataBase(DataBaseManager.java:79)
11-30 16:02:19.008: E/AndroidRuntime(968): at com.example.applicationdatabase.DataBaseManager.<init>(DataBaseManager.java:39)
11-30 16:02:19.008: E/AndroidRuntime(968): at com.example.applicationdatabase.DataBaseManager.instance(DataBaseManager.java:55)
11-30 16:02:19.008: E/AndroidRuntime(968): at com.example.applicationdatabase.DBActivity.onCreate(DBActivity.java:35)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.Activity.performCreate(Activity.java:5104)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
11-30 16:02:19.008: E/AndroidRuntime(968): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
11-30 16:02:19.008: E/AndroidRuntime(968): ... 11 more
最佳答案
这是从 Assest 文件夹中读取数据库的工作代码。唯一的问题是无法找到 PATH。
希望对大家有所帮助，如有疑问请私信我...
package net.learn2develop.Databases;
import java.io.IOException;
import android.app.Activity;
import android.database.Cursor;
import android.database.SQLException;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class DatabasesActivity extends Activity {
protected static final String TAG = null;
private Button insertButton;
private Button updateButton;
private Button deleteButton;
private Button displayButton;
boolean status = false;
private EditText name;
private EditText email;
protected int value1;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter myDbHelper = new DBAdapter(null);
myDbHelper = new DBAdapter(this);
insertButton = (Button) findViewById(R.id.btnInsert);
updateButton = (Button) findViewById(R.id.btnUpdate);
deleteButton = (Button) findViewById(R.id.btnDelete);
displayButton = (Button) findViewById(R.id.btnDisplay);
name = (EditText) findViewById(R.id.edit_name);
email = (EditText) findViewById(R.id.edit_email);
// --- inserting ------
insertButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (name.getText().toString().trim().length() == 0)
{
Toast msg = Toast.makeText(getBaseContext(),
"Please Enter Name ", Toast.LENGTH_LONG);
msg.show();
}
else if (email.getText().toString().trim().length() == 0)
{
Toast msg = Toast.makeText(getBaseContext(),
"Please Enter Email", Toast.LENGTH_LONG);
msg.show();
}
else
insertRecord();
}
});
// --------Deleting the Records -----------
deleteButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
deleteRecord();
}
});
// --- Displaying the Records -------
displayButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
DisplayRecord();
}
});
updateButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (name.getText().toString().trim().length() == 0)
{
Toast msg = Toast.makeText(getBaseContext(),
"Please Enter Name ", Toast.LENGTH_LONG);
msg.show();
}
else if (email.getText().toString().trim().length() == 0)
{
Toast msg = Toast.makeText(getBaseContext(),
"Please Enter Email", Toast.LENGTH_LONG);
msg.show();
}
else
{
updateRecord();
}
}
});
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
} catch (SQLException sqle) {
throw sqle;
}
}
protected void DisplayRecord() {
DBAdapter myDbHelper1 = new DBAdapter(null);
myDbHelper1.openDataBase();
Cursor c = myDbHelper1.getAllContacts();
if (c.moveToFirst()) {
do {
DisplayContact(c);
} while (c.moveToNext());
}
myDbHelper1.close();
}
protected void updateRecord() {
String Name = fetchName();
String Email = fetchEmail();
DBAdapter myDbHelper1 = new DBAdapter(null);
myDbHelper1.openDataBase();
if (myDbHelper1.updateContact(1, Name, Email))
{
Toast msg = Toast.makeText(getBaseContext(),
"Update Successfully ", Toast.LENGTH_LONG);
msg.show();
}
else
{
Toast msg = Toast.makeText(getBaseContext(),
"Update Failed ", Toast.LENGTH_LONG);
msg.show();
}
myDbHelper1.close();
}
protected void deleteRecord() {
DBAdapter myDbHelper1 = new DBAdapter(null);
myDbHelper1.openDataBase();
if (myDbHelper1.deleteContact(27))
{
Toast msg = Toast.makeText(getBaseContext(),
"Delete Successfully ", Toast.LENGTH_LONG);
msg.show();
}
else
{
Toast msg = Toast.makeText(getBaseContext(),
"Delete Failed ", Toast.LENGTH_LONG);
msg.show();
}
myDbHelper1.close();
}
protected void insertRecord() {
String Name = fetchName();
String Email = fetchEmail();
DBAdapter myDbHelper1 = new DBAdapter(null);
myDbHelper1.openDataBase();
long id = myDbHelper1.insertContact(Name, Email);
myDbHelper1.close();
Toast msg = Toast.makeText(getBaseContext(),
"Record: " + id + " Successfully inserted", Toast.LENGTH_LONG);
msg.show();
name.setText("");
email.setText("");
}
public void DisplayContact(Cursor c) {
Toast.makeText(
this,
"id: " + c.getString(0) + "\n" + "Name: " + c.getString(1)
+ "\n" + "Email: " + c.getString(2), Toast.LENGTH_LONG)
.show();
}
public String fetchName()
{
String Name = name.getText().trim().toString();
if (Name.contentEquals(name.getHint()))
{
return " ";
}
else
{
return Name;
}
}
public String fetchEmail()
{
String Email = email.getText().trim().toString();
if (Email.contentEquals(email.getHint()))
{
return " ";
}
else
{
return Email;
}
}
}
关于android - 无法在 Android 中打开数据库(预创建)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13642833/