How can I make that after pressing the button, in the middle of the app is a random preset text?

    body: Container(
        child: Column(children: <Widget>[
      SizedBox(
        height: 10,
      ),

After pressing this Button a _random Text should be show in the center. My problem is that it doesnot work.

      Padding(
        padding: EdgeInsets.only(top: 8),
        child: Row(
          crossAxisAlignment: CrossAxisAlignment.center,
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: <Widget>[
            RawMaterialButton(
              onPressed: () {},
              child: IconButton(
                icon: new Icon(Icons.add, size: 22,),
                color: Colors.white,
                onPressed: () {},
              ),