I am trying to practise on the loader and content provider i have a database of students that contains (name , degree) in the activity_main.xml i have a recyclerview and 2 editText one for name other for degree my target is that when a user click on the button the name will appear in the recyclerview here's my logcat
FATAL EXCEPTION: main Process: com.example.abdelmagied.myapplication, PID: 16160 java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.abdelmagied.myapplication.recyclerview.swapcursor(android.database.Cursor)' on a null object reference at com.example.abdelmagied.myapplication.MainActivity.onLoadFinished(MainActivity.java:97) at com.example.abdelmagied.myapplication.MainActivity.onLoadFinished(MainActivity.java:17) at android.support.v4.app.LoaderManagerImpl$LoaderInfo.callOnLoadFinished(LoaderManager.java:476) at android.support.v4.app.LoaderManagerImpl$LoaderInfo.onLoadComplete(LoaderManager.java:444) at android.support.v4.content.Loader.deliverResult(Loader.java:126) at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:105) at android.support.v4.content.CursorLoader.deliverResult(CursorLoader.java:37) at android.support.v4.content.AsyncTaskLoader.dispatchOnLoadComplete(AsyncTaskLoader.java:255) at android.support.v4.content.AsyncTaskLoader$LoadTask.onPostExecute(AsyncTaskLoader.java:80) at android.support.v4.content.ModernAsyncTask.finish(ModernAsyncTask.java:485) at android.support.v4.content.ModernAsyncTask$InternalHandler.handleMessage(ModernAsyncTask.java:502) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
this is my mainactivity class
package com.example.abdelmagied.myapplication;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor>{
public static final String[] MAIN_STUDENT_PROJECTION = {
studentContract.StudentEntry._ID ,
studentContract.StudentEntry.COLUMN_NAME ,
studentContract.StudentEntry.COLUMN_DEGREE ,
};
public static final int INDEX_COLUMN_ID = 0;
public static final int INDEX_COLUMN_NAME = 1;
public static final int INDEX_COLUMN_DEGREE = 2;
private recyclerview recyclerAdapter;
private int mposition = RecyclerView.NO_POSITION;
public static final int ID_STUDNET_LOADER = 99;
// details of the recyclerview
RecyclerView recycler;
RecyclerView.Adapter myadapter;
RecyclerView.LayoutManager mymanager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// adjust the recyclerview
recycler = (RecyclerView) findViewById(R.id.recyclerid);
myadapter = new recyclerview(this);
mymanager = new LinearLayoutManager(this);
recycler.setAdapter(myadapter);
recycler.setLayoutManager(mymanager);
getSupportLoaderManager().initLoader(ID_STUDNET_LOADER , null , this);
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
switch(id)
{
case ID_STUDNET_LOADER :
Uri Query = studentContract.StudentEntry.CONTENT_URI;
return new CursorLoader(this ,
Query ,
MAIN_STUDENT_PROJECTION ,
null ,
null ,
null
);
default:
throw new RuntimeException("Loader is not implemented : " + id);
}
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
recyclerAdapter.swapcursor(data);
if(mposition == RecyclerView.NO_POSITION) mposition = 0;
recycler.smoothScrollToPosition(mposition);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
recyclerAdapter.swapcursor(null);
}
public void addtodatabase(View view) {
EditText name = (EditText) findViewById(R.id.name);
EditText degree=(EditText) findViewById(R.id.degree);
// make a contentvalues and put name , degree , salary on it...
ContentValues values = new ContentValues();
values.put(studentContract.StudentEntry.COLUMN_NAME , name.getText().toString());
values.put(studentContract.StudentEntry.COLUMN_DEGREE , degree.getText().toString());
getContentResolver().insert(studentContract.StudentEntry.CONTENT_URI , values);
}
}
here's the recyclerview adapter
package com.example.abdelmagied.myapplication;
import android.content.Context;
import android.database.Cursor;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
/**
* Created by AbdELMagied on 8/4/2017.
*/
public class recyclerview extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
Context context;
private Cursor mycursor;
public recyclerview(Context context) {
this.context = context;
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.recyclerrow , parent , false);
return new viewholder(view);
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
mycursor.move(position);
viewholder myholder = (viewholder) holder;
myholder.mytxt.setText(mycursor.getString(MainActivity.INDEX_COLUMN_NAME));
}
void swapcursor(Cursor mycurso)
{
this.mycursor = mycurso;
notifyDataSetChanged();
}
@Override
public int getItemCount() {
if(mycursor == null) return 0;
return mycursor.getCount();
}
public class viewholder extends RecyclerView.ViewHolder
{
public TextView mytxt;
public viewholder(View itemView) {
super(itemView);
mytxt = (TextView) itemView.findViewById(R.id.textView);
}
}
}
here's my content provider
package com.example.abdelmagied.myapplication;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.support.annotation.Nullable;
import android.text.TextUtils;
/**
* Created by AbdELMagied on 8/4/2017.
*/
public class studentprovider extends ContentProvider {
databaseopenhelper mydatabase;
static final int STUDENT = 100;
static final int STUDENT_WITH_ID = 101;
private UriMatcher urimatcher = matcher();
private UriMatcher matcher() {
UriMatcher mymatcher = new UriMatcher(UriMatcher.NO_MATCH);
mymatcher.addURI(studentContract.authority, "student", STUDENT);
mymatcher.addURI(studentContract.authority, "student/#", STUDENT_WITH_ID);
return mymatcher;
}
@Override
public boolean onCreate() {
mydatabase = new databaseopenhelper(getContext());
return true;
}
@Nullable
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Cursor returncursor;
switch (urimatcher.match(uri)) {
case STUDENT:
returncursor = mydatabase.getReadableDatabase().query(
studentContract.StudentEntry.TABLE_NAME,
projection,
selection,
selectionArgs,
null,
null,
sortOrder
);
break;
case STUDENT_WITH_ID:
String where = "_id = " + uri.getLastPathSegment() + (!TextUtils.isEmpty(selection)? " AND " + selection : "");
returncursor = mydatabase.getReadableDatabase().query(
studentContract.StudentEntry.TABLE_NAME,
projection,
where,
selectionArgs,
null,
null,
sortOrder
);
break;
default:
throw new UnsupportedOperationException("not found uri " + uri);
}
returncursor.setNotificationUri(getContext().getContentResolver() , uri);
return returncursor;
}
@Nullable
@Override
public String getType(Uri uri) {
return null;
}
@Nullable
@Override
public Uri insert(Uri uri, ContentValues values) {
long rowid = mydatabase.getWritableDatabase().insert(studentContract.StudentEntry.TABLE_NAME, null , values);
if(rowid > 0)
{
Uri _uri = ContentUris.withAppendedId(studentContract.StudentEntry.CONTENT_URI, rowid);
getContext().getContentResolver().notifyChange(_uri, null);
return _uri;
}
throw new SQLException("Faild to add a record " + uri);
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
if(selection == "") selection= "1";
int numberofdeleted = 0;
switch (urimatcher.match(uri))
{
case STUDENT:
String where = "_id = " + uri.getLastPathSegment() + (!TextUtils.isEmpty(selection)? "AND " + selection : "");
numberofdeleted = mydatabase.getWritableDatabase().delete("students" , where , selectionArgs);
break;
default:
throw new UnsupportedOperationException("uri not found " + uri);
}
if(numberofdeleted != 0)
{
getContext().getContentResolver().notifyChange(uri , null);
}
return numberofdeleted;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
return 0;
}
}
here's the database class
package com.example.abdelmagied.myapplication;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/**
* Created by AbdELMagied on 8/4/2017.
*/
public class databaseopenhelper extends SQLiteOpenHelper {
public databaseopenhelper(Context context) {
super(context, "student.db", null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
final String SQL_CREATE_STUDENT_TABLE =
"CREATE TABLE " + studentContract.StudentEntry.TABLE_NAME + " (" +
studentContract.StudentEntry._ID + " INTEGER PRIMARY KEY , " +
studentContract.StudentEntry.COLUMN_NAME + " TEXT , " +
studentContract.StudentEntry.COLUMN_DEGREE + " TEXT ); " ;
db.execSQL(SQL_CREATE_STUDENT_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop database if exists student");
onCreate(db);
}
}
here's studentcontract class
package com.example.abdelmagied.myapplication;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.support.annotation.Nullable;
import android.text.TextUtils;
/**
* Created by AbdELMagied on 8/4/2017.
*/
public class studentprovider extends ContentProvider {
databaseopenhelper mydatabase;
static final int STUDENT = 100;
static final int STUDENT_WITH_ID = 101;
private UriMatcher urimatcher = matcher();
private UriMatcher matcher() {
UriMatcher mymatcher = new UriMatcher(UriMatcher.NO_MATCH);
mymatcher.addURI(studentContract.authority, "student", STUDENT);
mymatcher.addURI(studentContract.authority, "student/#", STUDENT_WITH_ID);
return mymatcher;
}
@Override
public boolean onCreate() {
mydatabase = new databaseopenhelper(getContext());
return true;
}
@Nullable
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Cursor returncursor;
switch (urimatcher.match(uri)) {
case STUDENT:
returncursor = mydatabase.getReadableDatabase().query(
studentContract.StudentEntry.TABLE_NAME,
projection,
selection,
selectionArgs,
null,
null,
sortOrder
);
break;
case STUDENT_WITH_ID:
String where = "_id = " + uri.getLastPathSegment() + (!TextUtils.isEmpty(selection)? " AND " + selection : "");
returncursor = mydatabase.getReadableDatabase().query(
studentContract.StudentEntry.TABLE_NAME,
projection,
where,
selectionArgs,
null,
null,
sortOrder
);
break;
default:
throw new UnsupportedOperationException("not found uri " + uri);
}
returncursor.setNotificationUri(getContext().getContentResolver() , uri);
return returncursor;
}
@Nullable
@Override
public String getType(Uri uri) {
return null;
}
@Nullable
@Override
public Uri insert(Uri uri, ContentValues values) {
long rowid = mydatabase.getWritableDatabase().insert(studentContract.StudentEntry.TABLE_NAME, null , values);
if(rowid > 0)
{
Uri _uri = ContentUris.withAppendedId(studentContract.StudentEntry.CONTENT_URI, rowid);
getContext().getContentResolver().notifyChange(_uri, null);
return _uri;
}
throw new SQLException("Faild to add a record " + uri);
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
if(selection == "") selection= "1";
int numberofdeleted = 0;
switch (urimatcher.match(uri))
{
case STUDENT:
String where = "_id = " + uri.getLastPathSegment() + (!TextUtils.isEmpty(selection)? "AND " + selection : "");
numberofdeleted = mydatabase.getWritableDatabase().delete("students" , where , selectionArgs);
break;
default:
throw new UnsupportedOperationException("uri not found " + uri);
}
if(numberofdeleted != 0)
{
getContext().getContentResolver().notifyChange(uri , null);
}
return numberofdeleted;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
return 0;
}
}
recyclerAdapter is never instantiated. onCreate would be an ideal place to instantiate this object of type recyclerview.