不断获取空指针异常，找不到源

Question

E/AndroidRuntime(2886): FATAL EXCEPTION: main
E/AndroidRuntime(2886): java.lang.NullPointerException
E/AndroidRuntime(2886):     at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)
E/AndroidRuntime(2886):     at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
E/AndroidRuntime(2886):     at android.widget.AbsListView.obtainView(AbsListView.java:2033)
E/AndroidRuntime(2886):     at android.widget.GridView.onMeasure(GridView.java:1026)
E/AndroidRuntime(2886):     at android.view.View.measure(View.java:12728)
E/AndroidRuntime(2886):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1369)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1017)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:555)
E/AndroidRuntime(2886):     at android.view.View.measure(View.java:12728)
E/AndroidRuntime(2886):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1369)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:660)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:553)
E/AndroidRuntime(2886):     at android.view.View.measure(View.java:12728)
E/AndroidRuntime(2886):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)
E/AndroidRuntime(2886):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
E/AndroidRuntime(2886):     at android.view.View.measure(View.java:12728)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:812)
E/AndroidRuntime(2886):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:553)
E/AndroidRuntime(2886):     at android.view.View.measure(View.java:12728)
E/AndroidRuntime(2886):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)
E/AndroidRuntime(2886):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
E/AndroidRuntime(2886):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2092)
E/AndroidRuntime(2886):     at android.view.View.measure(View.java:12728)
E/AndroidRuntime(2886):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1064)
E/AndroidRuntime(2886):     at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2442)
E/AndroidRuntime(2886):     at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(2886):     at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(2886):     at android.app.ActivityThread.main(ActivityThread.java:4424)
E/AndroidRuntime(2886):     at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(2886):     at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(2886):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
E/AndroidRuntime(2886):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
E/AndroidRuntime(2886):     at dalvik.system.NativeStart.main(Native Method)

there's the Logcat

and here's (hopefully) relevant code. Where I think the problem originates

public class Main extends Activity {
    private static final int REQUEST_CODE = 0;
    List<String> custom1 = new ArrayList<String>();
    List<String> custom2 = new ArrayList<String>();
    List<String> custom3 = new ArrayList<String>();
    String title = null;
    ArrayAdapter<String> a1;
    ArrayAdapter<String> a2;
    ArrayAdapter<String> a3;
    Button b_1;
    Button b_2;
    Button b_3;
    NotesDataSource dataSource;
    MySQLiteHelper dbHelper;
    SQLiteDatabase db;
    int id;
    int position;
    boolean newNote;

    static int ADAPTER = 1;

     GridView gv;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        String savedText = null;

        Bundle extras = getIntent().getExtras();
        id = extras.getInt("id");
        position = extras.getInt("pos");
        newNote = !extras.getBoolean("load");

        dataSource = new NotesDataSource(this);

        final EditText tv = (EditText)findViewById(R.id.textArea);
        final EditText title_tv = (EditText)findViewById(R.id.noteTitle);

        if(!newNote){
            savedText = extras.getString("textData");
            title = extras.getString("title");
            if(savedText.length() != 0){
                tv.append(savedText);
            }
            if(title.length() != 0){
                title_tv.append(title);
            }
        }
        if(dataSource.getArray1() != null){
            custom1.addAll(dataSource.getArray1());
        }
        else{
            custom1.addAll(Arrays.asList(getResources().getStringArray(R.array.SymbolArray)));
        }
        if(dataSource.getArray2() != null){
            custom2.addAll(dataSource.getArray2());
        } 
        else{
            custom2.addAll(Arrays.asList(getResources().getStringArray(R.array.SymbolArray)));
        }
        if(dataSource.getArray3() != null){
            custom3.addAll(dataSource.getArray3());
        }
        else{
            custom3.addAll(Arrays.asList(getResources().getStringArray(R.array.SymbolArray)));
        }

        a1 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,custom1);
        a2 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,custom2);
        a3 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,custom3);

        gv = (GridView)findViewById(R.id.gridView);
        gv.setAdapter(a1);
        ADAPTER = 1;
        gv.isFocusable();
        gv.isFocusableInTouchMode();

        gv.setOnItemClickListener(new OnItemClickListener(){
            public void onItemClick(AdapterView<?> parent, View v, int position, long id){
                switch(ADAPTER){
                case 1:
                    tv.append(custom1.get(position));
                    break;
                case 2:
                    tv.append(custom2.get(position));
                    break;
                case 3:
                    tv.append(custom3.get(position));
                default:
                    break;
                }
            }
        });

        b_1 = (Button)findViewById(R.id.button1);
        b_2 = (Button)findViewById(R.id.button2);
        b_3 = (Button)findViewById(R.id.button3);
        Button b_save = (Button)findViewById(R.id.save_button);

        b_1.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                gv.setAdapter(a1);
                ADAPTER = 1;

            }
        });

        b_2.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                gv.setAdapter(a2);
                ADAPTER = 2;
            }
        });

        b_3.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                gv.setAdapter(a3);
                ADAPTER = 3;

            }
        });

        b_save.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                if(newNote == false){
                    dataSource.open();
                    String text = tv.getText().toString();
                    if(title.length() != 0){
                        title = title_tv.getText().toString();
                        dataSource.updateString(text,title,id);
                    }
                    else{
                        dataSource.updateString(text, "no title", id);
                    }
                    dataSource.close();
                }
                else{
                    dataSource.open();
                    String text = tv.getText().toString();
                    title = title_tv.getText().toString();

                    dataSource.createString(text, title);
                    newNote = false;
                    dataSource.close();
                }
            }
        });    

    }

Here's the three array methods

    public List<String> getArray1(){
            ArrayList<String> array1 = new ArrayList<String>();

            open();
            Cursor cursor = db.query(MySQLiteHelper.TABLE_ARRAY, new String[]{MySQLiteHelper.COLUMN_ARRAY_1}, null, null, null, null, null);
            cursor.moveToFirst();
            while(!cursor.isAfterLast()){
                String data = cursorToArrayString(cursor);
                array1.add(data);
                cursor.moveToNext();
            }
            //make sure to close the cursor
            close();
            return array1;
        }

        public List<String> getArray2(){
            ArrayList<String> array2 = new ArrayList<String>();

            open();
            Cursor cursor = db.query(MySQLiteHelper.TABLE_ARRAY, new String[]{MySQLiteHelper.COLUMN_ARRAY_2}, null,null,null,null,null);
            cursor.moveToFirst();
            while(!cursor.isAfterLast()){
                String data = cursorToArrayString(cursor);
                array2.add(data);
                cursor.moveToNext();
            }
            //make sure to close the cursor
            close();
            return array2;
        }

        public List<String> getArray3(){
            ArrayList<String> array3 = new ArrayList<String>();

            open();
            Cursor cursor = db.query(MySQLiteHelper.TABLE_ARRAY, new String[]{MySQLiteHelper.COLUMN_ARRAY_3}, null,null,null,null,null);
            cursor.moveToFirst();
            while(!cursor.isAfterLast()){
                String data = cursorToArrayString(cursor);
                array3.add(data);
                cursor.moveToNext();
            }
            //make sure to close the cursor
            close();
            return array3;
        }


and finally how they're updated 


public void updateArray(String[] array1, String[] array2, String[] array3){

        db.delete(MySQLiteHelper.TABLE_ARRAY, null, null);

        ContentValues values1 = new ContentValues();
        for(int i = 0; i < array1.length; i++){
            values1.put(MySQLiteHelper.COLUMN_ARRAY_1, array1[i]);
            int rows = db.update(MySQLiteHelper.TABLE_ARRAY, values1, MySQLiteHelper.COLUMN_ID + " = " + i, null);
            if(rows == 0){
                db.insert(MySQLiteHelper.TABLE_ARRAY, null, values1);
            }
        }


        ContentValues values2 = new ContentValues();
        for(int i = 0; i < array2.length; i++){
            values2.put(MySQLiteHelper.COLUMN_ARRAY_2, array2[i]);
            int rows = db.update(MySQLiteHelper.TABLE_ARRAY, values2, MySQLiteHelper.COLUMN_ID + " = " + i, null);
            if(rows == 0){
                db.insert(MySQLiteHelper.TABLE_ARRAY, null, values2);
            }
        }

        ContentValues values3 = new ContentValues();
        for(int i = 0; i < array3.length; i++){
            values3.put(MySQLiteHelper.COLUMN_ARRAY_3, array3[i]);
            int rows = db.update(MySQLiteHelper.TABLE_ARRAY, values3, MySQLiteHelper.COLUMN_ID + " = " + i, null);
            if(rows == 0){
                db.insert(MySQLiteHelper.TABLE_ARRAY, null, values3);
            }
        }
    }

go easy on me, this is my first time working with databases, but I'd love to know what the issues is, I've been working on this problem for days now

Answer 1

When does the exception happen? ON screen load? On a click?

I would simply run a debugger and put a breakpoint right before you create your Adapter instances. Make sure none of the strings in the arrays are null. That would be my guess.