'java.lang.NullPointerException: Attempt to invoke interface method 'void android.database.Cursor.close()' on a null object reference
https://github.com/kamaleshdas1997/MyPets
LOGCAT:-
Process: com.example.mypets, PID: 21583
java.lang.NullPointerException: Attempt to invoke interface method 'void android.database.Cursor.close()' on a null object reference
at com.example.mypets.CatlogActivity.displayDatabaseInfo(CatlogActivity.java:133)
at com.example.mypets.CatlogActivity.onStart(CatlogActivity.java:48)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1470)
at android.app.Activity.performStart(Activity.java:7170)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3061)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1906)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6863)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:537)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2020-12-13 09:54:55.751 496-496/? E/SELinux: avc: denied { find } for service=opdiagnose pid=21583 uid=10312 scontext=u:r:untrusted_app:s0:c56,c257,c512,c768 tcontext=u:object_r:opdiagnose_service:s0 tclass=service_manager permissive=0
2020-12-13 09:54:55.751 496-496/? E/SELinux: avc: denied { find } for service=opdiagnose pid=21583 uid=10312 scontext=u:r:untrusted_app:s0:c56,c257,c512,c768 tcontext=u:object_r:opdiagnose_service:s0 tclass=service_manager permissive=0
CatlogActivity:
package com.example.mypets;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.content.ContentValues;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import com.example.mypets.data.PetContract.PetEntry;
import com.example.mypets.data.PetDBHelper;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
public class CatlogActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_catlog_activity);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent i = new Intent(CatlogActivity.this , EditorActivty.class);
startActivity(i);
}
});
}
@Override
protected void onStart() {
super.onStart();
displayDatabaseInfo();
}
/**
* Temporary helper method to display information in the onscreen TextView about the state of
* the pets database.
*/
private void displayDatabaseInfo() {
// To access our database, we instantiate our subclass of SQLiteOpenHelper
// and pass the context, which is the current activity.
// Create and/or open a database to read from it
// SQLiteDatabase db = mDbHelper.getReadableDatabase();
TextView displayView = (TextView) findViewById(R.id.text_view_pet);
//Projection
String[] projection ={
PetEntry._ID,
PetEntry.COLUMN_PET_NAME,
PetEntry.COLUMN_PET_BREED,
PetEntry.COLUMN_PET_GENDER,
PetEntry.COLUMN_PET_WEIGHT
};
// Perform this raw SQL query "SELECT * FROM pets"
// // to get a Cursor that contains all rows from the pets table.
Cursor cursor = getContentResolver().query(
PetEntry.CONTENT_URI,
projection,
null,
null,
null
);
try {
// Create a header in the Text View that looks like this:
//
// The pets table contains <number of rows in Cursor> pets.
// _id - name - breed - gender - weight
//
// In the while loop below, iterate through the rows of the cursor and display
// the information from each column in this order.
displayView.setText("The pets table contains " + cursor.getCount() + " pets.\n\n");
displayView.append(PetEntry._ID + " - " +
PetEntry.COLUMN_PET_NAME + " - " +
PetEntry.COLUMN_PET_BREED + " - " +
PetEntry.COLUMN_PET_GENDER + " - " +
PetEntry.COLUMN_PET_WEIGHT + "\n");
// Figure out the index of each column
int idColumnIndex = cursor.getColumnIndex(PetEntry._ID);
int nameColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_NAME);
int breedColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_BREED);
int genderColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_GENDER);
int weightColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_WEIGHT);
// Iterate through all the returned rows in the cursor
while (cursor.moveToNext()) {
// Use that index to extract the String or Int value of the word
// at the current row the cursor is on.
int currentID = cursor.getInt(idColumnIndex);
String currentName = cursor.getString(nameColumnIndex);
String currentBreed = cursor.getString(breedColumnIndex);
int currentGender = cursor.getInt(genderColumnIndex);
int currentWeight = cursor.getInt(weightColumnIndex);
// Display the values from each column of the current row in the cursor in the TextView
displayView.append(("\n" + currentID + " - " +
currentName + " - " +
currentBreed + " - " +
currentGender + " - " +
currentWeight));
}
}
finally {
// Always close the cursor when you're done reading from it. This releases all its
// resources and makes it invalid.
cursor.close();
}
}
private void insertPet() {
ContentValues contentValues = new ContentValues();
contentValues.put(PetEntry.COLUMN_PET_NAME, "name");
contentValues.put(PetEntry.COLUMN_PET_BREED, "breed");
contentValues.put(PetEntry.COLUMN_PET_GENDER, PetEntry.GENDER_MALE);
contentValues.put(PetEntry.COLUMN_PET_WEIGHT, 7);
Uri newURI = getContentResolver().insert(PetEntry.CONTENT_URI, contentValues);
Log.v("CatalogActivity" , "New Role ID" + newURI);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_catalog, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
switch (item.getItemId())
{
case R.id.action_delete_all_entries:
insertPet();
return true;
case R.id.action_insert_dummy_data:
insertPet();
displayDatabaseInfo();
return true;
}
return super.onOptionsItemSelected(item);
}
}
Solution 1:[1]
After Building your program from the Guthub link, it's obvious your query to the Database doesn't match any element.
Commented out everywhere you make invoke a method on the cursor object and added the line of code below
if(cursor==null)
Toast.makeText(getApplicationContext(),"null cursor",0).show();
And it's obvious it's null
Solution 2:[2]
- List item
@Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { // Get readable database SQLiteDatabase database = mDbHelper.getReadableDatabase();
// This cursor will hold the result of the query
Cursor cursor;
// Figure out if the URI matcher can match the URI to a specific code
int match = sUriMatcher.match(uri);
switch (match)
{
case PETS:
// For the PETS code, query the pets table directly with the given
// projection, selection, selection arguments, and sort order. The cursor
// could contain multiple rows of the pets table.
cursor=database.query(PetEntry.TABLE_NAME,projection,
selection,selectionArgs,null,null,sortOrder);
break;
case PET_ID:
// For the PET_ID code, extract out the ID from the URI.
// For an example URI such as "content://com.example.android.pets/pets/3",
// the selection will be "_id=?" and the selection argument will be a
// String array containing the actual ID of 3 in this case.
//
// For every "?" in the selection, we need to have an element in the selection
// arguments that will fill in the "?". Since we have 1 question mark in the
// selection, we have 1 String in the selection arguments' String array.
selection = PetEntry._ID + "=?";
selectionArgs = new String[] { String.valueOf(ContentUris.parseId(uri)) };
// This will perform a query on the pets table where the _id equals 3 to return a
// Cursor containing that row of the table.
cursor = database.query(PetEntry.TABLE_NAME, projection, selection, selectionArgs,
null, null, sortOrder);
break;
default:
throw new IllegalArgumentException("Cannot query unknown URI " + uri);
}
return cursor;
}
Sources
This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.
Source: Stack Overflow
| Solution | Source |
|---|---|
| Solution 1 | |
| Solution 2 |