Android, How to get/set layout parameters?

Question

In my application I have a conversation room. All of my messages should be aligned to right while the rest should be left aligned.

Single row of my list is like this:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/llContainer" >

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:background="@drawable/speech_bubble_orange"
        android:id="@+id/llGroup" >

            <TextView
                android:id="@+id/message_text"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:shadowColor="@color/message_textShadow"
                android:shadowDx="1"
                android:shadowDy="1"
                android:text="Medium Text"
                android:textColor="@color/message_textColor"
                android:textSize="20sp" />

            <TextView
                android:id="@+id/message_date"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="@string/temp_date"
                android:gravity="right"
                android:layout_marginLeft="4dp"
                android:layout_marginRight="4dp"/>
    </LinearLayout>

</LinearLayout>

getView() of my adapter is like this:

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    ViewHolder holder;

    if (convertView == null) {
        convertView = myInflater.inflate(R.layout.list_message_row, null);
        holder = new ViewHolder();

        holder.tvMessageBody = (TextView) convertView.findViewById(R.id.message_text);
        holder.tvMessageDate = (TextView) convertView.findViewById(R.id.message_date);
        holder.llContainer = (LinearLayout) convertView.findViewById(R.id.llContainer);
        holder.llGroup = (LinearLayout) convertView.findViewById(R.id.llGroup);

        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }

    holder.tvMessageBody.setText(messageList.get(position).getMessageBody());
    String date = messageList.get(position).getSentDate();
    holder.tvMessageDate.setText(formatFanciedDate(date));

    LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) holder.llContainer.getLayoutParams();
    try {
        if(messageList.get(position).isMine()) {
            holder.llGroup.setBackgroundResource(R.drawable.speech_bubble_green);
            params.gravity = Gravity.RIGHT;
        }
        //If not mine then it is from sender to show orange background and align to left
        else {
            holder.llGroup.setBackgroundResource(R.drawable.speech_bubble_orange);
            params.gravity = Gravity.LEFT;
        }

        holder.llContainer.setLayoutParams(params);

    } catch (NullPointerException e) {
        e.printStackTrace();
    }

    return convertView;
}

I think everything should be fine however when I run the application NullPointerException happens and points to params.gravity = Gravity.RIGHT; or params.gravity = Gravity.LEFT; (depends on isMine() method).

What you think? Where is my mistake? Any suggestion would be appreciated.

Answer 1

getLayoutParams() will return null until the view is attached to its parent.

Try to create the layout params with its constructor rather than using getLayoutParams().

Answer 2

Use RelativeLayout params and set gravity like this, it will work.

RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT, RelativeLayout.TRUE);

This is working for me in my application.