다이얼로그 포지션 값이 이상한데요??

Question

다이얼로그 ok 클릭시 which가 왜 항상 -1이죠???

 

public void show_blelist() {
        Log.e("NOTICE", "DEVICE LIST : " + mDeviceList);
        ListAdapter adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDeviceList);
        final CharSequence[] items = new CharSequence[adapter.getCount()];
        for(int i=0 ; i< adapter.getCount() ; i++){
            items[i] = mDeviceList.get(i);
        }

        //final CharSequence[] items = {"red", "green", "blue"};

        AlertDialog.Builder dialog = new AlertDialog.Builder(this);
        dialog.setIcon(R.mipmap.ic_launcher);
        dialog.setTitle("BLE DEVICE LIST");
        dialog.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Toast.makeText(Info_activity.this, "which : " + which, Toast.LENGTH_SHORT).show();
                Device elem = Engine.getInstance().getDevices().get(which+1);
                Log.e("NOTICE", "elem :: " + elem);
                if(!elem.isConnected()) {
                    Log.e("NOTICE", "elem connecting....");
                    mBluetoothLeService.connect(elem);
                }
                else {
                    Log.e("NOTICE", "elem is already connected...");
                }
                startServiceCharacteristic(elem.getAddress());
            }
        });
        dialog.setNegativeButton("Cancel",new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });
        dialog.setIcon(R.mipmap.ic_launcher);
        dialog.setSingleChoiceItems(items, -1, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Toast.makeText(Info_activity.this, "select : " + items[which], Toast.LENGTH_SHORT).show();
            }
        });
        dialog.show();
    }

 

 

위 소스에서

dialog.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Toast.makeText(Info_activity.this, "which : " + which, Toast.LENGTH_SHORT).show();

여기서 which 값이 항상 -1 입니다..

3개의 선택창에서 두번째 선택해도..세번째 선택해도.....

제가 뭘 잘못하고 있는건가요?>