canvas scroll

I am writing a solitaire app. I use a canvas to draw everything on the
screen. Sometimes a pile of cards will get big and extend below the
bottom of the screen. I would like to make the canvas scrollable so
the user can access those cards.

Main Activity.
Java:

package com.maulinpathare.solitaire;

public class Solitaire extends Activity{
    /** Called when the activity is first created. */
     private Context mContext;
     private GameView mG;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mContext = this;
        setContentView(R.layout.main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        boolean result = super.onCreateOptionsMenu(menu);
        menu.add(0, 1, 0, R.string.newGame);
        menu.add(0, 2, 0, R.string.exitGame);
        return result;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case 1:
          mG = new GameView(this);
          setContentView(mG);
            return true;
        case 2:
            finish();
            return true;
        }
        return false;
    }

}//end class

GameView Class
This is where everything happens
I have removed most of the game logic...
Java:

package com.maulinpathare.solitaire;

public class GameView extends ScrollView implements OnTouchListener{
     private Deck mD;
     private boolean mInit, mDone;
     private Stack<Card> mPile1, mPile2, mPile3, mPile4, mPile5,
mPile6, mPile7,
                              mOpenPile, mEndPile1, mEndPile2,
mEndPile3, mEndPile4, mTemp;
     private Canvas mCanvas;
     private int mPile;
     private boolean mPickUp, mVictory;
     private Card mCard;
     private final int mSpacing = 22;
     private Paint rectPaint, wonPaint1, wonPaint2;

     public GameView(Context context) {
        super(context);
                    //initialize everything needed for the game
    }

    @Override
    protected void onDraw(Canvas canvas) {
     mCanvas = canvas;
     if(mInit){
          initialize();
          mInit = false;
     }
        //draw stuff...

    }//end onDraw

    public boolean onTouch(View v, MotionEvent event){
     int eventAction = event.getAction();
     int x = Math.round(event.getX());
     int y = Math.round(event.getY());

     switch(eventAction){
     case MotionEvent.ACTION_DOWN:
                    //check if touch has happened on one of the card
piles
          break; //end case action_touch

     case MotionEvent.ACTION_MOVE:
                    //if card touched move it
          break; //end case action_move

     case MotionEvent.ACTION_UP:
                    //check if legal move has been made
          break; //end case action_up

     }//end switch(event)

     invalidate();
     return true;
    }//end onTouch
}

Where and how should I implement screen scrolling? I would like the
user to be able to slide their finger across the screen in the
direction they want to scroll.