上下文操作栏无法从SQLite删除所选项目

Question

CAB unable to delete the data from cursor adapter

public class History extends ListActivity{

private ReminderDB mDbHelper;
List selections = new ArrayList();
int count = 0;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.history);

    mDbHelper = new ReminderDB(this);
    mDbHelper.open();
    fillData();
    registerForContextMenu(getListView());
}

private void fillData() {
    final Cursor remindersCursor = mDbHelper.fetchAllHistoryEvents();
    startManagingCursor(remindersCursor);
    // an array for the fields to show in the list row (now only the TITLE)
    String[] from = new String[]{ReminderDB.KEY_TITLE};
    // and an array of the fields for each list row
    int[] to = new int[]{R.id.row1};
    // a simple cursor adapter and set it to display
    final HistoryCustomCursorAdapter history = new HistoryCustomCursorAdapter(this, R.layout.history_list_row, remindersCursor, from, to);
    setListAdapter(history);
    getListView().setChoiceMode(AbsListView.CHOICE_MODE_MULTIPLE_MODAL);
    getListView().setMultiChoiceModeListener(new AbsListView.MultiChoiceModeListener() {
        @Override
        public void onItemCheckedStateChanged(ActionMode mode, int position, long id, boolean checked) {
            if(checked){
                selections.add(history.getItem(position));
                count++;
                mode.setTitle(count+ " Selected");
            }else{
                selections.remove(history.getItem(position));
                count--;
                mode.setTitle(count+ " Selected");
            }
        }

        @Override
        public boolean onCreateActionMode(ActionMode mode, Menu menu) {
            MenuInflater menuInflater = getMenuInflater();
            menuInflater.inflate(R.menu.contextual_menu, menu);
            return true;
        }

        @Override
        public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
            return false;
        }

        @Override
        public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
            if (item.getItemId()==R.id.item_delete){
                AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
                mDbHelper.deleteHistory(info.id);
                history.notifyDataSetChanged();
                mode.finish();
            }
            fillData();
            return true;
        }

        @Override
        public void onDestroyActionMode(ActionMode mode) {
            count = 0;
            selections.clear();
        }
    });
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
    super.onActivityResult(requestCode, resultCode, intent);
    fillData();
}
}

This is the error message i getting:

11-08 14:24:03.475 6934-6934/com.example.windchin.digitalbrain E/AndroidRuntime﹕ FATAL EXCEPTION: main java.lang.NullPointerException at com.example.windchin.digitalbrain.History$1.onActionItemClicked(History.java:83) at android.widget.AbsListView$MultiChoiceModeWrapper.onActionItemClicked(AbsListView.java:7680) at com.android.internal.policy.impl.PhoneWindow$DecorView$ActionModeCallbackWrapper.onActionItemClicked(PhoneWindow.java:3299) at com.android.internal.app.ActionBarImpl$ActionModeImpl.onMenuItemSelected(ActionBarImpl.java:1009) at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:735) at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152) at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:874) at com.android.internal.view.menu.ActionMenuView.invokeItem(ActionMenuView.java:630) at com.android.internal.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:200) at android.view.View.perf ormClick(View.java:4475) at android.view.View$PerformClick.run(View.java:18786) at android.os.Handler.handleCallback(Handler.java:730) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:176) at android.app.ActivityThread.main(ActivityThread.java:5419) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862) at dalvik.system.NativeStart.main(Native Method)

This is cursor adapter class

public class HistoryCustomCursorAdapter extends SimpleCursorAdapter {
    private Context context;
    private ReminderDB mDbHelper;
    private int layout;

    public HistoryCustomCursorAdapter (Context context, int layout, Cursor c, String[] from, int[] to) {
        super(context, layout, c, from, to);
        this.context = context;
        this.layout = layout;
        mDbHelper = new ReminderDB(context);
        mDbHelper.open();
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {

        final LayoutInflater inflater = LayoutInflater.from(context);
        View rowView = inflater.inflate(layout, parent, false);

        int titleCol = cursor.getColumnIndex(ReminderDB.KEY_TITLE);
        String title = cursor.getString(titleCol);
        TextView textView1 = (TextView) rowView.findViewById(R.id.row1);
        TextView textView2 = (TextView) rowView.findViewById(R.id.row2);
        ImageView imageView = (ImageView) rowView.findViewById(R.id.icon);

        textView1.setText(title);

        String Hdate = cursor.getString(cursor.getColumnIndex(ReminderDB.KEY_DATE_TIME));
        String latitude = cursor.getString(cursor.getColumnIndex(ReminderDB.KEY_LATITUDE));
        String longitude = cursor.getString(cursor.getColumnIndex(ReminderDB.KEY_LONGITUDE));

        if(Hdate != null)
            imageView.setImageResource(R.drawable.cclock);
        else
            imageView.setImageResource(R.drawable.maps);

        if(Hdate != null)
        {
            textView2.setText(Hdate);
        }
        else
        {
            Cursor c = mDbHelper.fetchLocation(latitude, longitude);
            String location = c.getString(c.getColumnIndex(ReminderDB.KEY_LOCATION));
            int option = Integer.parseInt(cursor.getString(cursor.getColumnIndex(ReminderDB.KEY_LOCATIONOPTION)));
            String locationOption;
            if (option == 0){
                locationOption = "When I Arrive";
            } else {
                locationOption = "When I Leave";
            }
            textView2.setText(locationOption + ": " + location);
        }
        return rowView;
    }
}

Answer 1

Based on your comment, then you have a problem at these lines:

            AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
            mDbHelper.deleteHistory(info.id);

This means that your info object is null and your call to item.getMenuInfo() is not working.

That means your HistoryCustomCursorAdapter is not setting this value correctly. You have not posted the code for that object, but I think this should be sufficient to allow you to find the error.