我正在集成数据库来保存和存储以后要检索的基本联系信息.但是,我的应用程序现在在启动时崩溃,所以我甚至无法验证是否正在创建表等.
05-05 16:39:50.671 11631-11631/treehouse.greenlight E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: treehouse.greenlight,PID: 11631
java.lang.RuntimeException: Unable to start activity ComponentInfo{treehouse.greenlight/treehouse.greenlight.Home_screen}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.sqliteDatabase android.content.Context.openorCreateDatabase(java.lang.String,int,android.database.sqlite.sqliteDatabase$CursorFactory,android.database.DatabaseErrorHandler)' on a null object reference
at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2205)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2255)
at android.app.ActivityThread.access$800(ActivityThread.java:142)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1203)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5118)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:794)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.sqliteDatabase android.content.Context.openorCreateDatabase(java.lang.String,android.database.DatabaseErrorHandler)' on a null object reference
at android.database.sqlite.sqliteOpenHelper.getDatabaseLocked(sqliteOpenHelper.java:224)
at android.database.sqlite.sqliteOpenHelper.getWritableDatabase(sqliteOpenHelper.java:164)
at treehouse.greenlight.MyDBHandler.addContact(MyDBHandler.java:54)
at treehouse.greenlight.ContactsFragment.onCreateLoader(ContactsFragment.java:117)
at android.support.v4.app.LoaderManagerImpl.createLoader(LoaderManager.java:490)
at android.support.v4.app.LoaderManagerImpl.createAndInstallLoader(LoaderManager.java:499)
at android.support.v4.app.LoaderManagerImpl.initLoader(LoaderManager.java:553)
at treehouse.greenlight.ContactsFragment.onActivityCreated(ContactsFragment.java:71)
at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1797)
at android.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:979)
at android.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:1138)
at android.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:1120)
at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1929)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
at android.app.Activity.performStart(Activity.java:5285)
at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2178)
数据库处理程序代码：
public class MyDBHandler extends sqliteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "contactsDB.db";
public static final String TABLE_CONTACTS = "contacts";
private Context context;
public static final String COLUMN_ID = "_id";
public static final String COLUMN_NAME = "name";
public static final String COLUMN_PHONE = "phone";
public static final String COLUMN_STATUS = "status";
public static final String COLUMN_BLURB = "blurb";
public MyDBHandler(Context context,String name,CursorFactory factory,int version) {
super(context,DATABASE_NAME,factory,DATABASE_VERSION);
}
@Override
public void onCreate (sqliteDatabase db){
String CREATE_CONTACTS_TABLE = "CREATE TABLE " +
TABLE_CONTACTS + "("
+ COLUMN_ID + " INTEGER PRIMARY KEY," + ContactsContract.CommonDataKinds.Phone.disPLAY_NAME
+ " TEXT," + ContactsContract.CommonDataKinds.Phone.NUMBER + " INTEGER,"
+ COLUMN_STATUS + " TEXT," + COLUMN_BLURB
+ " TEXT" + ");";
db.execsql(CREATE_CONTACTS_TABLE);
}
@Override
public void onUpgrade (sqliteDatabase db,int oldVersion,int newVersion){
db.execsql("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
onCreate(db);
}
public void addContact(ContactsDb contacts) {
ContentValues values = new ContentValues();
values.put(COLUMN_NAME,contacts.getName());
values.put(COLUMN_PHONE,contacts.getPhone());
values.put(COLUMN_STATUS,contacts.getStatus());
values.put(COLUMN_BLURB,contacts.getBlurb());
sqliteDatabase db = this.getWritableDatabase();
db.insert(TABLE_CONTACTS,null,values);
}
logcat说问题是sqliteDatabase db = this.getWriteableDatabase();
这也是我违规的Contactsfragment：
public class ContactsFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor> {
private CursorAdapter mAdapter;
private Context context;
TextView idView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// create adapter once
Context context = getActivity();
int layout = R.layout.activity_list_item_1;
Cursor c = null; // there is no cursor yet
int flags = 0; // no auto-requery! Loader requeries.
mAdapter = new SimpleCursorAdapter(context,layout,c,FROM,TO,flags);
}
public void ContactsDb(Context context) {
this.context=context;
}
Uri contentUri = ContactsContract.CommonDataKinds.Phone.CONTENT_URI;
String[] PROJECTION = {
ContactsContract.Contacts.HAS_PHONE_NUMBER,ContactsContract.Contacts._ID,// _ID is always required
ContactsContract.CommonDataKinds.Phone.disPLAY_NAME_PRIMARY,// that is what we want to display
Contacts.TIMES_CONTACTED,ContactsContract.CommonDataKinds.Phone.NUMBER
};
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
// each time we are started use our listadapter
setlistadapter(mAdapter);
// and tell loader manager to start loading
getLoaderManager().initLoader(0,this);
}
// columns requested from the database
// and name should be displayed in the text1 textview in item layout
public String[] has_phone = {ContactsContract.Contacts.HAS_PHONE_NUMBER};
String phone = "0";
int dbPhone = 0;
private final String[] FROM = {Contacts.disPLAY_NAME_PRIMARY,ContactsContract.CommonDataKinds.Phone.NUMBER};
private final int[] TO = {android.R.id.text1,dbPhone};
public void newContact (View view) {
MyDBHandler dbHandler = new MyDBHandler(context,1);
String name = Contacts.disPLAY_NAME_PRIMARY;
int dbPhone =
Integer.parseInt(phone);
String status ="";
String blurb ="";
ContactsDb contacts =
new ContactsDb(name,dbPhone,status,blurb);
dbHandler.addContact(contacts);
}
@Override
public Loader<Cursor> onCreateLoader(int id,Bundle args) {
Context context = this.context;
// load from the "Contacts table"
MyDBHandler dbHandler = new MyDBHandler(context,1);
String name = Contacts.disPLAY_NAME_PRIMARY;
int phone = Integer.parseInt(ContactsContract.CommonDataKinds.Phone.NUMBER);
String status ="Busy";
String blurb ="N/A";
ContactsDb contacts =
new ContactsDb(name,blurb);
dbHandler.addContact(contacts);
// no sub-selection,no sort order,simply every row
// projection says we want just the _id and the name column
return new CursorLoader(getActivity(),contentUri,PROJECTION,ContactsContract.Contacts.HAS_PHONE_NUMBER + " =? AND " + Contacts.TIMES_CONTACTED + ">=?",// This is selection string,we're looking for records that HAS_PHONE_NUMBER is 1
new String[]{"1","0"},// 1 means that contact has a phone number & 60 is the amount of times contacted (arbitrary - needs to be fixed before release)
null);
}
最后,这是ContactsDB类：
public ContactsDb(String name,int phone,String status,String blurb) {
this._name = name;
this._phone = phone;
this._status = status;
this._blurb = blurb;
非常感谢任何帮助 – 我认为问题在于我的Context为null.我只是不确定为什么它会在我的MyDBHandler文件中定义它.截至目前,我无法验证是否正在创建数据库,更不用说保存数据了.
干杯&感谢您的时间和耐心,
希亚姆
解决方法
看起来你不小心创建了一个上下文局部变量而不是使用实例变量.
因此,当您将其传递给MyDBHandler时,context为null,因此当您调用this.getWritableDatabase()时,它为null.因此,您可以在日志中看到NullPointerException：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.sqliteDatabase android.content.Context.openorCreateDatabase(java.lang.String,android.database.DatabaseErrorHandler)' on a null object reference
at android.database.sqlite.sqliteOpenHelper.getDatabaseLocked(sqliteOpenHelper.java:224)
at android.database.sqlite.sqliteOpenHelper.getWritableDatabase(sqliteOpenHelper.java:164)
尝试将所有与Context相关的代码移动到onActivityCreated()以确保您具有有效的Context,并确保使用实例变量而不是局部变量：
public class ContactsFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor> {
private CursorAdapter mAdapter;
private Context context; //this is the Context you will use
TextView idView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// create adapter once
//Context context = getActivity(); //Here was the problem
//int layout = R.layout.activity_list_item_1;
//Cursor c = null; // there is no cursor yet
//int flags = 0; // no auto-requery! Loader requeries.
//mAdapter = new SimpleCursorAdapter(context,ContactsContract.CommonDataKinds.Phone.NUMBER
};
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
//Add this here:
context = getActivity(); //use the instance variable
int layout = R.layout.activity_list_item_1;
Cursor c = null; // there is no cursor yet
int flags = 0; // no auto-requery! Loader requeries.
mAdapter = new SimpleCursorAdapter(context,flags);
// each time we are started use our listadapter
setlistadapter(mAdapter);
// and tell loader manager to start loading
getLoaderManager().initLoader(0,dbPhone};
public void newContact (View view) {
//context should Now be valid:
MyDBHandler dbHandler = new MyDBHandler(context,blurb);
dbHandler.addContact(contacts);
}
//........