Android的自定义内容提供程序

Question

Hey guys,im working on a simple quiz and im gone crazy !! The problem is that everything is working (database created as it shoulds) except when i am trying to get string from database shows java.lang.NullPointerException.I checked the uri is corrected and the number of items in array!!I am trying to find out why this is happening for 5 hours and i am stucked here!!!I dont know what elso to do!!Your help is more than appreciated!!

My main class where i am trying to get string is that one with bold

        Uri newUri = ContentUris.withAppendedId(
        QuestionsProvider.CONTENT_URI,
        this.currentQuestion);
        Log.d(TAG, "SHOWQUESTION " + " URI="+newUri.toString());

        Cursor cursor = cr.query(newUri,
        null, null, null, null);

            if (cursor.moveToFirst()) {
        **question.setText(cursor.getString(
                QuestionsProvider.QUESTION_COLUMN)); //HERE I AM GETTING THE ERROR
        currentAnswer = cursor.getString(
                QuestionsProvider.ANSWER_COLUMN);**
        submit.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                String text;
                String answerGiven =
                answer.getText().toString();
                answer.setText("");
                if (answerGiven.
                        equalsIgnoreCase(currentAnswer))
                        {text = "Correct";
                        }else{
                        text = "Wrong - "+currentAnswer;
                        Toast.makeText(getApplicationContext(),
                        text, Toast.LENGTH_SHORT).show();
                        }
                        }});
            }
            cursor.close();
        dialog.show();

and in my manifest i add succesfully the provider and is loading as it should!! Why this error happens??I can see anything wrong!!

Answer 1

It doesn't look like you're specifying a projection in the query:

Cursor cursor = cr.query(newUri, null, null, null, null);

Try adding a projection with the columns you want returned:

Cursor cursor = cr.query(newUri, new String[] {KEY_ID, KEY_QUESTION, KEY_ANSWER}, null, null, null);

Answer 2

I found the solution guys! Thank you for helping me unstucking heh :P This is the solution i found!!

String columns[] = new String[] { QuestionsProvider.KEY_QUESTION, QuestionsProvider.KEY_ANSWER };
            Uri mUri = QuestionsProvider.CONTENT_URI;
            Cursor cur = managedQuery(mUri, columns, // Which columns to return
                    QuestionsProvider.KEY_ID+"="+currentQuestionNumber, // WHERE clause; which rows to return(all rows)
                    null, // WHERE clause selection arguments (none)
                    null // Order-by clause (ascending by name)