访问数据库时，会抛出NullPointerException。
以下是创建db的代码：
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String KEY_CREATE_TABLE = "CREATE TABLE IF NOT EXISTS {0} ({1})";
public static final String KEY_DROP_TABLE = "DROP TABLE IF EXISTS {0}";
private Context context;
Activity C;
private static final int CURRENT_DB_VERSION = 1;
private static final String DB_NAME = "vrochat.db";
SQLiteDatabase Db1;
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, CURRENT_DB_VERSION);
this.context = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
createUserTable(db);
createMessageTable(db);
createDialogTable(db);
// // //Raj
createTimelineTable(db);
createNewsFeedTable(db);
createProfileTable(db);
createProfilemediaListTable(db);
createFriendinfoTable(db);
//samson
createMultiImagePostTable(db);
//
this.Db1=db;
}
private void createMultiImagePostTable(SQLiteDatabase db) {
// TODO Auto-generated method stub
StringBuilder MultiImagePostTablefields = new StringBuilder();
MultiImagePostTablefields.append(MultiImagePostTable.Cols.ID)
.append(" INTEGER PRIMARY KEY, ")
.append(MultiImagePostTable.Cols.IMAGE).append(" TEXT, ")
.append(MultiImagePostTable.Cols.IMAGE_CREATED_AT).append(" TEXT, ")
.append(MultiImagePostTable.Cols.IMAGE_THUMB).append(" TEXT, ")
.append(MultiImagePostTable.Cols.POST_ID).append(" TEXT ");
createTable(db, MultiImagePostTable.TABLE_NAME,
MultiImagePostTablefields.toString());
}
private void createUserTable(SQLiteDatabase db) {
StringBuilder userTableFields = new StringBuilder();
userTableFields.append(UserTable.Cols.ID)
.append(" INTEGER PRIMARY KEY AUTOINCREMENT, ")
.append(UserTable.Cols.USER_ID).append(" INTEGER, ")
.append(UserTable.Cols.FULL_NAME).append(" TEXT, ")
.append(UserTable.Cols.EMAIL).append(" TEXT, ")
.append(UserTable.Cols.LOGIN).append(" TEXT, ")
.append(UserTable.Cols.PHONE)
.append(" TEXT, ")
.append(UserTable.Cols.WEB_SITE)
.append(" TEXT, ")
.append(UserTable.Cols.CUSTOM_DATA)
.append(" TEXT, ")
.append(UserTable.Cols.LAST_REQUEST_AT)
.append(" TEXT, ")
.append(UserTable.Cols.EXTERNAL_ID)
.append(" TEXT, ")
// .append(UserTable.Cols.FACEBOOK_ID).append(" INTEGER, ")
// .append(UserTable.Cols.TWITTER_ID).append(" INTEGER, ")
.append(UserTable.Cols.BLOB_ID).append(" INTEGER, ")
.append(UserTable.Cols.AVATAR_URL).append(" TEXT, ")
.append(UserTable.Cols.STATUS).append(" TEXT, ")
.append(UserTable.Cols.IS_ONLINE).append(" INTEGER");
createTable(db, UserTable.TABLE_NAME, userTableFields.toString());
}
private void createMessageTable(SQLiteDatabase db) {
StringBuilder messageTableFields = new StringBuilder();
messageTableFields.append(MessageTable.Cols.ID)
.append(" INTEGER PRIMARY KEY, ")
.append(MessageTable.Cols.MESSAGE_ID).append(" TEXT UNIQUE, ")
.append(MessageTable.Cols.DIALOG_ID).append(" TEXT, ")
.append(MessageTable.Cols.SENDER_ID).append(" INTEGER, ")
.append(MessageTable.Cols.BODY).append(" TEXT, ")
.append(MessageTable.Cols.TIME).append(" LONG, ")
.append(MessageTable.Cols.ATTACH_FILE_ID).append(" TEXT, ")
.append(MessageTable.Cols.ATTACH_TYPE).append(" TEXT, ")
.append(MessageTable.Cols.IS_READ).append(" INTEGER, ")
.append(MessageTable.Cols.IS_DELIVERED).append(" INTEGER, ")
.append(MessageTable.Cols.IS_SYNC).append(" INTEGER, ")
.append(MessageTable.Cols.FRIENDS_NOTIFICATION_TYPE)
.append(" INTEGER");
createTable(db, MessageTable.TABLE_NAME, messageTableFields.toString());
}
private void createDialogTable(SQLiteDatabase db) {
StringBuilder dialogTableFields = new StringBuilder();
dialogTableFields.append(DialogTable.Cols.ID)
.append(" INTEGER PRIMARY KEY AUTOINCREMENT, ")
.append(DialogTable.Cols.DIALOG_ID).append(" TEXT, ")
.append(DialogTable.Cols.ROOM_JID_ID).append(" TEXT, ")
.append(DialogTable.Cols.NAME).append(" TEXT, ")
.append(DialogTable.Cols.COUNT_UNREAD_MESSAGES)
.append(" INTEGER, ").append(DialogTable.Cols.LAST_MESSAGE)
.append(" TEXT, ")
.append(DialogTable.Cols.LAST_MESSAGE_USER_ID)
.append(" LONG, ").append(DialogTable.Cols.LAST_DATE_SENT)
.append(" LONG, ").append(DialogTable.Cols.OCCUPANTS_IDS)
.append(" TEXT, ").append(DialogTable.Cols.PHOTO_URL)
.append(" TEXT, ").append(DialogTable.Cols.VROId)
.append(" TEXT, ").append(DialogTable.Cols.TYPE)
.append(" INTEGER");
createTable(db, DialogTable.TABLE_NAME, dialogTableFields.toString());
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
dropTable(db, UserTable.TABLE_NAME);
dropTable(db, MessageTable.TABLE_NAME);
dropTable(db, DialogTable.TABLE_NAME);
onCreate(db);
}
public void dropTable(SQLiteDatabase db, String name) {
String query = MessageFormat
.format(DatabaseHelper.KEY_DROP_TABLE, name);
db.execSQL(query);
}
public void createTable(SQLiteDatabase db, String name, String fields) {
String query = MessageFormat.format(DatabaseHelper.KEY_CREATE_TABLE,
name, fields);
db.execSQL(query);
}
// ///////////////Raj
private void createProfilemediaListTable(SQLiteDatabase db) {
// TODO Auto-generated method stub
StringBuilder ProfileMediaListTablefields = new StringBuilder();
ProfileMediaListTablefields.append(ProfileMedialistTable.Cols.ID)
.append(" INTEGER PRIMARY KEY AUTOINCREMENT, ")
.append(ProfileMedialistTable.Cols.USERID).append(" INTEGER, ")
.append(ProfileMedialistTable.Cols.IMAGETHUMB)
.append(" TEXT, ").append(ProfileMedialistTable.Cols.IMAGEURL)
.append(" TEXT, ").append(ProfileMedialistTable.Cols.TYPE)
.append(" TEXT ");
createTable(db, ProfileMedialistTable.TABLE_NAME,
ProfileMediaListTablefields.toString());
}
private void createProfileTable(SQLiteDatabase db) {
// TODO Auto-generated method stub
StringBuilder ProfileTableFields = new StringBuilder();
ProfileTableFields.append(ProfileTable.Cols.ABOUT).append(" TEXT, ")
.append(ProfileTable.Cols.CHANNELCOUNT).append(" TEXT, ")
.append(ProfileTable.Cols.CITY).append(" TEXT, ")
.append(ProfileTable.Cols.COLLEGEAT).append(" TEXT, ")
.append(ProfileTable.Cols.COUNTRY)
.append(" TEXT, ")
.append(ProfileTable.Cols.DOB)
.append(" TEXT, ")
.append(ProfileTable.Cols.EMAIL)
.append(" TEXT, ")
.append(ProfileTable.Cols.FIRSTNAME)
.append(" TEXT, ")
.append(ProfileTable.Cols.FRIENDSCOUNT)
.append(" TEXT, ")
.append(ProfileTable.Cols.FRIENDSHIPSTATUS)
.append(" TEXT, ")
.append(ProfileTable.Cols.GENDER)
.append(" TEXT, ")
.append(ProfileTable.Cols.HOBBY)
.append(" TEXT, ")
.append(ProfileTable.Cols.IMAGECOUNT)
.append(" TEXT, ")
.append(ProfileTable.Cols.INTERESTS)
.append(" TEXT, ")
.append(ProfileTable.Cols.LASTNAME)
.append(" TEXT, ")
// .append(ProfileTable.Cols.MEDIALIST).append(" TEXT, ")
.append(ProfileTable.Cols.MEMBERSINCE).append(" TEXT, ")
.append(ProfileTable.Cols.PRIVACY).append(" TEXT, ")
.append(ProfileTable.Cols.PROFILEPICURL).append(" TEXT, ")
.append(ProfileTable.Cols.QBID).append(" TEXT, ")
.append(ProfileTable.Cols.RELATIONSHIPSTATUS).append(" TEXT, ")
.append(ProfileTable.Cols.SCHOOLAT).append(" TEXT, ")
.append(ProfileTable.Cols.STATE).append(" TEXT, ")
.append(ProfileTable.Cols.TIMELINEPIC).append(" TEXT, ")
.append(ProfileTable.Cols.USERID)
.append(" INTEGER PRIMARY KEY, ")
.append(ProfileTable.Cols.USERNAME).append(" TEXT, ")
.append(ProfileTable.Cols.VIDEOCOUNT).append(" TEXT, ")
.append(ProfileTable.Cols.WORKSAT).append(" TEXT ");
createTable(db, ProfileTable.TABLE_NAME, ProfileTableFields.toString());
}
private void createNewsFeedTable(SQLiteDatabase db) {
// TODO Auto-generated method stub
StringBuilder NewsFeedTableFields = new StringBuilder();
NewsFeedTableFields.append(TimelineTable.Cols.ID).append(" INTEGER, ")
.append(NewsFeedTable.Cols.VROID).append(" INTEGER, ")
.append(NewsFeedTable.Cols.FIRST_NAME).append(" TEXT, ")
.append(NewsFeedTable.Cols.LAST_NAME).append(" TEXT, ")
.append(NewsFeedTable.Cols.POST_TITLE).append(" TEXT, ")
.append(NewsFeedTable.Cols.POST_CONTENT).append(" TEXT, ")
.append(NewsFeedTable.Cols.POST_TYPE).append(" TEXT, ")
.append(NewsFeedTable.Cols.POST_IMAGEURL).append(" TEXT, ")
.append(NewsFeedTable.Cols.POST_IMAGEURL_THUMB)
.append(" TEXT, ").append(NewsFeedTable.Cols.POST_VIDEOURL)
.append(" TEXT, ").append(NewsFeedTable.Cols.POST_CREATED)
.append(" TEXT, ").append(NewsFeedTable.Cols.POST_UPDATED)
.append(" TEXT, ").append(NewsFeedTable.Cols.LIKE_COUNT)
.append(" INTEGER, ").append(NewsFeedTable.Cols.COMMENT_COUNT)
.append(" INTEGER, ").append(NewsFeedTable.Cols.SHARE_COUNT)
.append(" INTEGER, ").append(NewsFeedTable.Cols.IS_MY_POST)
.append(" TEXT, ").append(NewsFeedTable.Cols.IS_SHARED)
.append(" TEXT, ").append(NewsFeedTable.Cols.IS_LIKED)
.append(" TEXT, ")
.append(NewsFeedTable.Cols.FROM_USER_FIRSTNAME)
.append(" TEXT, ").append(NewsFeedTable.Cols.FROM_USER_ID)
.append(" TEXT, ")
.append(NewsFeedTable.Cols.FROM_USER_LAST_NAME)
.append(" TEXT, ")
.append(NewsFeedTable.Cols.FROM_USER_PROFILE_PIC)
.append(" TEXT, ")
.append(NewsFeedTable.Cols.TO_USER_FIRST_NAME)
.append(" TEXT, ").append(NewsFeedTable.Cols.TO_USER_LAST_NAME)
.append(" TEXT, ")
.append(NewsFeedTable.Cols.TO_USER_PROFILE_PIC)
.append(" TEXT, ").append(NewsFeedTable.Cols.USERS_POSTID)
.append(" INTEGER PRIMARY KEY, ")
.append(NewsFeedTable.Cols.YOUTUBE_VIDEO_URL).append(" TEXT, ")
.append(NewsFeedTable.Cols.POST__VIDEO_URL_THUMB)
.append(" TEXT");
createTable(db, NewsFeedTable.TABLE_NAME,
NewsFeedTableFields.toString());
}
private void createTimelineTable(SQLiteDatabase db) {
// TODO Auto-generated method stub
StringBuilder timeLineTableFields = new StringBuilder();
timeLineTableFields.append(TimelineTable.Cols.ID).append(" INTEGER, ")
.append(TimelineTable.Cols.VROID).append(" INTEGER, ")
.append(TimelineTable.Cols.FIRST_NAME).append(" TEXT, ")
.append(TimelineTable.Cols.LAST_NAME).append(" TEXT, ")
.append(TimelineTable.Cols.POST_TITLE).append(" TEXT, ")
.append(TimelineTable.Cols.POST_CONTENT).append(" TEXT, ")
.append(TimelineTable.Cols.POST_TYPE).append(" TEXT, ")
.append(TimelineTable.Cols.POST_IMAGEURL).append(" TEXT, ")
.append(TimelineTable.Cols.POST_IMAGEURL_THUMB)
.append(" TEXT, ").append(TimelineTable.Cols.POST_VIDEOURL)
.append(" TEXT, ").append(TimelineTable.Cols.POST_CREATED)
.append(" TEXT, ").append(TimelineTable.Cols.POST_UPDATED)
.append(" TEXT, ").append(TimelineTable.Cols.LIKE_COUNT)
.append(" INTEGER, ").append(TimelineTable.Cols.COMMENT_COUNT)
.append(" INTEGER, ").append(TimelineTable.Cols.SHARE_COUNT)
.append(" INTEGER, ").append(TimelineTable.Cols.IS_MY_POST)
.append(" TEXT, ").append(TimelineTable.Cols.IS_SHARED)
.append(" TEXT, ").append(TimelineTable.Cols.IS_LIKED)
.append(" TEXT, ")
.append(TimelineTable.Cols.FROM_USER_FIRSTNAME)
.append(" TEXT, ").append(TimelineTable.Cols.FROM_USER_ID)
.append(" TEXT, ")
.append(TimelineTable.Cols.FROM_USER_LAST_NAME)
.append(" TEXT, ")
.append(TimelineTable.Cols.FROM_USER_PROFILE_PIC)
.append(" TEXT, ")
.append(TimelineTable.Cols.TO_USER_FIRST_NAME)
.append(" TEXT, ").append(TimelineTable.Cols.TO_USER_LAST_NAME)
.append(" TEXT, ")
.append(TimelineTable.Cols.TO_USER_PROFILE_PIC)
.append(" TEXT, ").append(TimelineTable.Cols.USERS_POSTID)
.append(" INTEGER PRIMARY KEY, ")
.append(TimelineTable.Cols.YOUTUBE_VIDEO_URL).append(" TEXT, ")
.append(TimelineTable.Cols.POST__VIDEO_URL_THUMB)
.append(" TEXT");
createTable(db, TimelineTable.TABLE_NAME,
timeLineTableFields.toString());
}
private void createFriendinfoTable(SQLiteDatabase db) {
// TODO Auto-generated method stub
StringBuilder FriendInfoTablefields = new StringBuilder();
FriendInfoTablefields.append(FriendinfoTable.Cols.ID)
.append(" INTEGER PRIMARY KEY, ")
.append(FriendinfoTable.Cols.FIRST_NAME).append(" TEXT, ")
.append(FriendinfoTable.Cols.LAST_NAME).append(" TEXT, ")
.append(FriendinfoTable.Cols.USER_NAME).append(" TEXT, ")
.append(FriendinfoTable.Cols.EMAIL).append(" TEXT, ")
.append(FriendinfoTable.Cols.USER_PROFILE_PIC)
.append(" TEXT, ")
.append(FriendinfoTable.Cols.USER_TIMELINE_PIC)
.append(" TEXT, ").append(FriendinfoTable.Cols.COUNTRY)
.append(" TEXT, ").append(FriendinfoTable.Cols.STATE)
.append(" TEXT, ").append(FriendinfoTable.Cols.CITY)
.append(" TEXT, ").append(FriendinfoTable.Cols.ABOUT)
.append(" TEXT, ").append(FriendinfoTable.Cols.GENDER)
.append(" TEXT, ").append(FriendinfoTable.Cols.DATEOFBIRTH)
.append(" TEXT, ")
.append(FriendinfoTable.Cols.FRIENDSHIP_STATUS)
.append(" TEXT, ").append(FriendinfoTable.Cols.QUICKBLOX_ID)
.append(" TEXT ");
createTable(db, FriendinfoTable.TABLE_NAME,
FriendInfoTablefields.toString());
}
//aswathy
public void getfriendsdata()
{
Cursor c=Db1.rawQuery("SELECT * FROM friendinfotable",null);
try
{
//put cursor on the first position
c.moveToFirst();
//fetching all records from cursor until reaching last record
while(!c.isAfterLast())
{
/*
* Display record on the screen
* Note : here in the cursor there are two columns.
* So be careful while fetching record.
* If no column is there, it will give you exception
*/
Toast.makeText(context,c.getString(0)+ " "+c.getString(1),Toast.LENGTH_SHORT).show();
//moving cursor to next record
c.moveToNext();
}
//closing cursor
c.close();
}catch(Exception e)
{
Log.d("Error", "error in cursor");
e.printStackTrace();
}
}
这就是它的调用方式：
public class FindPeopleFragment extends BaseFragment{
....
private void loadMoreData() {
DatabaseHelper dh=new DatabaseHelper(getActivity());
dh.getfriendsdata();
}
}
以下是显示异常的logcat输出：
java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference at below line
Cursor c=Db1.rawQuery("SELECT * FROM friendinfotable",null);
答案 0 :(得分：4)
在运行onCreate之前，似乎未调用getfriendsdata();。因为Db1仅在onCreate()中初始化。
您必须致电Cursor c= getReadableDatabase().rawQuery("SELECT * FROM friendinfotable",null);
答案 1 :(得分：1)
在创建数据库时，在only once中调用onCreate（）。
Cursor c=Db1.rawQuery("SELECT * FROM friendinfotable",null);
因此，当应用程序第二次打开时，您的数据库Db1实例将为null。
所以你需要使用数据库参考。
SQLiteDatabase Db1=getReadableDatabase();
然后致电。
Cursor c=Db1.rawQuery("SELECT * FROM friendinfotable",null);