public class MessageAdapter extends ArrayAdapter<ChatBubble> {
private Activity activity;
private List<ChatBubble> messages;
private int state;

public MessageAdapter(Activity context, int resource, List<ChatBubble> objects) {
    super(context, resource, objects);
    this.activity = context;
    this.messages = objects;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    LayoutInflater inflater = (LayoutInflater) activity.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);

    int layoutResource = 0; // determined by view type
    ChatBubble ChatBubble = getItem(position);
    int viewType = getItemViewType(position);

    switch(ChatBubble.myMessage()){
        case "0":
            layoutResource = R.layout.date_chat_bubble;
        break;
        case "1":
            layoutResource = R.layout.date_chat_bubble;
        break;
        case "2":
            layoutResource = R.layout.rx_chat_bubble;
        break;
    }

    if (convertView != null) {
        holder = (ViewHolder) convertView.getTag();
    } else {
        convertView = inflater.inflate(layoutResource, parent, false);
        holder = new ViewHolder(convertView);
        convertView.setTag(holder);
    }
    //set message content
    holder.nameRx.setText(ChatBubble.getISSDD());
    holder.msg.setText(ChatBubble.getContent());
    holder.stringDate.setText( ChatBubble.getstringDate());
    holder.stringTime.setText( ChatBubble.getstringTime());
    return convertView;
}

@Override
public int getViewTypeCount() {
    return 3;
}

@Override
public int getItemViewType(int position) {
    ChatBubble chatBubble = messages.get(position);
    switch (chatBubble.myMessage()){
        case "0":
            state = 1;
            break;

        case "1":
            state = 1;
            break;

        case "2":
            state = 0;
            break;
    }
    return state;
}

private class ViewHolder {

    private TextView msg;
    private TextView stringTime;
    private TextView stringDate;
    private TextView nameRx;

    public ViewHolder(View v) {
        msg = (TextView) v.findViewById(R.id.txt_msg);
        stringTime = (TextView) v.findViewById(R.id.time_msg);
        stringDate = (TextView) v.findViewById(R.id.date_msg);
        nameRx = (TextView) v.findViewById(R.id.name_rx);
    }
  }
}

public class ChatBubble {

private String content;
private String myMessage;
private String stringTime;
private String stringDate;
private String iSsDd;

public ChatBubble(String content, String myMessage, String stringTime, String stringDate, String iSsDd) {
    this.content = content;
    this.myMessage = myMessage;
    this.stringTime = stringTime;
    this.stringDate = stringDate;
    this.iSsDd = iSsDd;
}

public String getContent() {
    return content;
}

public String myMessage() {
    return myMessage;
}

public String getstringTime() { return stringTime;}

public String getstringDate() { return stringDate;}

public String getISSDD() { return iSsDd;}
}

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.wsalas.satmessenger.MessageAdapter.getView(MessageAdapter.java:55)
    at android.widget.AbsListView.obtainView(AbsListView.java:2828)
    at android.widget.ListView.makeAndAddView(ListView.java:1932)