我使用简单的应用程序开发了sqlite数据库连接。但是，当我尝试运行我的应用程序时，它显示“不幸的是app已停止”。我的数据库包含所有插入，更新，删除操作。我也发布了所有代码和logcat错误。
databasehandler.java
package com.example.database;
import java.util.ArrayList;
import java.util.List;
import com.example.androidsqlite.Contact;
import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
public class DatabaseHandler extends Activity
{
// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "contact";
// Contacts table name
private static final String TABLE_CONTACTS = "contact";
// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_PH_NO = "phone_number";
public DatabaseHandler(Context context)
{
super();
}
// Creating Tables
public void onCreate(SQLiteDatabase db)
{
String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
+ KEY_PH_NO + " TEXT" + ")";
db.execSQL(CREATE_CONTACTS_TABLE);
}
// Upgrading database
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
// Create tables again
onCreate(db);
}
// Adding new contact
public void addContact(Contact contact)
{
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName()); // Contact Name
values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone Number
// Inserting Row
db.insert(TABLE_CONTACTS, null, values);
db.close(); // Closing database connection
}
private SQLiteDatabase getWritableDatabase() {
// TODO Auto-generated method stub
return null;
}
// Getting single contact
public Contact getContact(int id)
{
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.query(TABLE_CONTACTS, new String[]
{ KEY_ID,
KEY_NAME,
KEY_PH_NO
}, KEY_ID + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
// return contact
return contact;
}
// Getting All Contacts
public List<Contact> getAllContacts()
{
List<Contact> contactList = new ArrayList<Contact>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_CONTACTS;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Contact contact = new Contact();
contact.setID(Integer.parseInt(cursor.getString(0)));
contact.setName(cursor.getString(1));
contact.setPhoneNumber(cursor.getString(2));
// Adding contact to list
contactList.add(contact);
} while (cursor.moveToNext());
}
// return contact list
return contactList;
}
// Getting contacts Count
public int getContactsCount()
{
String countQuery = "SELECT * FROM " + TABLE_CONTACTS;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();
// return count
return cursor.getCount();
}
// Updating single contact
public int updateContact(Contact contact)
{
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName());
values.put(KEY_PH_NO, contact.getPhoneNumber());
// updating row
return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
new String[] { String.valueOf(contact.getID()) });
}
// Deleting single contact
public void deleteContact(Contact contact)
{
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
new String[] { String.valueOf(contact.getID()) });
db.close();
}
}
logcat错误
02-13 12:51:59.280: D/Insert:(793): Inserting ..
02-13 12:51:59.300: D/AndroidRuntime(793): Shutting down VM
02-13 12:51:59.300: W/dalvikvm(793): threadid=1: thread exiting with uncaught exception (group=0xb4ac0b90)
02-13 12:51:59.320: E/AndroidRuntime(793): FATAL EXCEPTION: main
02-13 12:51:59.320: E/AndroidRuntime(793): Process: com.example.database, PID: 793
02-13 12:51:59.320: E/AndroidRuntime(793): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.database/com.example.database.MainActivity}: java.lang.NullPointerException
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.ActivityThread.access$700(ActivityThread.java:135)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.os.Handler.dispatchMessage(Handler.java:102)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.os.Looper.loop(Looper.java:137)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.ActivityThread.main(ActivityThread.java:4998)
02-13 12:51:59.320: E/AndroidRuntime(793): at java.lang.reflect.Method.invokeNative(Native Method)
02-13 12:51:59.320: E/AndroidRuntime(793): at java.lang.reflect.Method.invoke(Method.java:515)
02-13 12:51:59.320: E/AndroidRuntime(793): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
02-13 12:51:59.320: E/AndroidRuntime(793): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
02-13 12:51:59.320: E/AndroidRuntime(793): at dalvik.system.NativeStart.main(Native Method)
02-13 12:51:59.320: E/AndroidRuntime(793): Caused by: java.lang.NullPointerException
02-13 12:51:59.320: E/AndroidRuntime(793): at com.example.database.DatabaseHandler.addContact(DatabaseHandler.java:64)
02-13 12:51:59.320: E/AndroidRuntime(793): at com.example.database.MainActivity.onCreate(MainActivity.java:26)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.Activity.performCreate(Activity.java:5243)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-13 12:51:59.320: E/AndroidRuntime(793): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
02-13 12:51:59.320: E/AndroidRuntime(793): ... 11 more
02-13 12:53:25.212: I/Process(793): Sending signal. PID: 793 SIG: 9
02-13 12:53:34.512: D/Insert:(1053): Inserting ..
02-13 12:53:34.512: D/AndroidRuntime(1053): Shutting down VM
02-13 12:53:34.522: W/dalvikvm(1053): threadid=1: thread exiting with uncaught exception (group=0xb4ac0b90)
02-13 12:53:34.522: E/AndroidRuntime(1053): FATAL EXCEPTION: main
02-13 12:53:34.522: E/AndroidRuntime(1053): Process: com.example.database, PID: 1053
02-13 12:53:34.522: E/AndroidRuntime(1053): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.database/com.example.database.MainActivity}: java.lang.NullPointerException
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.ActivityThread.access$700(ActivityThread.java:135)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.os.Handler.dispatchMessage(Handler.java:102)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.os.Looper.loop(Looper.java:137)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.ActivityThread.main(ActivityThread.java:4998)
02-13 12:53:34.522: E/AndroidRuntime(1053): at java.lang.reflect.Method.invokeNative(Native Method)
02-13 12:53:34.522: E/AndroidRuntime(1053): at java.lang.reflect.Method.invoke(Method.java:515)
02-13 12:53:34.522: E/AndroidRuntime(1053): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
02-13 12:53:34.522: E/AndroidRuntime(1053): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
02-13 12:53:34.522: E/AndroidRuntime(1053): at dalvik.system.NativeStart.main(Native Method)
02-13 12:53:34.522: E/AndroidRuntime(1053): Caused by: java.lang.NullPointerException
02-13 12:53:34.522: E/AndroidRuntime(1053): at com.example.database.DatabaseHandler.addContact(DatabaseHandler.java:64)
02-13 12:53:34.522: E/AndroidRuntime(1053): at com.example.database.MainActivity.onCreate(MainActivity.java:26)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.Activity.performCreate(Activity.java:5243)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-13 12:53:34.522: E/AndroidRuntime(1053): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
02-13 12:53:34.522: E/AndroidRuntime(1053): ... 11 more
02-13 12:53:36.882: I/Process(1053): Sending signal. PID: 1053 SIG: 9
答案 0 :(得分：1)
看一下这个字符串：
SQLiteDatabase db = this.getWritableDatabase();
您尚未实施getWritableDatabase()方法，这就是您的db为null
编辑好的，您的DatabaseHandler写错了。它应该扩展SQLiteOpenHelper。在这种情况下，添加了getWritableDatabase函数的处理程序的基本示例如下：
public class DBWorker extends SQLiteOpenHelper {
private static String DB_PATH = "/data/data/<your app>/databases/";
private static String DB_NAME = "db.sqlite";
private SQLiteDatabase myDataBase;
private final Context myContext;
public DBWorker(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
public void getWritableDatabase() throws SQLException {
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
//do the stuff
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//do the stuff
}
}
答案 1 :(得分：0)
您尚未初始化某些内容，而该内容正在导致崩溃。看到这个错误：
Caused by: java.lang.NullPointerException
浏览代码，看看哪个变量未初始化