Enlarge the touch targets of small views in Android

gistfile1.java

import android.content.Context;
import android.graphics.Rect;
import android.view.TouchDelegate;
import android.view.View;

/**
 * <p>
 * Ensures minimum hitbox size of small touch targets. For example:
 * <p>
 * <code>
 * TouchDelegateAdjustment.adjustTouchSize(getActivity(), smallView);<br>
 * </code>
 * 
 * @see #adjustTouchSize(Context, View)
 * @version 2
 */
public class TouchDelegateAdjustment implements Runnable
{
   // 50 dp is about 9 mm in on screen size
   final private static int MIN_TOUCH_WIDTH_DP = 50;
   final private static int MIN_TOUCH_HEIGHT_DP = 50;
   private View delegate;
   private int topPadding;
   private int bottomPadding;
   private int leftPadding;
   private int rightPadding;

   /**
    * Constructor: Increase the hitbox to minimum of about 9mm by 9mm size with the delegate in the middle.
    * 
    * @param ctx The context from which to retrieve the screen density information
    * @param smallView The view on which a alter the hitbox
    */
   public TouchDelegateAdjustment(Context ctx, View smallView)
   {
      this(ctx, smallView, MIN_TOUCH_WIDTH_DP, MIN_TOUCH_HEIGHT_DP);
   }

   /**
    * Constructor: Increase the hitbox to minimum of about 9mm by 9mm size with the delegate in the middle.
    * 
    * @param ctx The context from which to retrieve the screen density information
    * @param smallView The view one which a alter the hitbox
    * @param minWidth Minimum width of the hit rects in dip
    * @param minHeight Minimum height of the hit rects in dip
    */
   public TouchDelegateAdjustment(Context ctx, View smallView, int minWdith, int minHeight)
   {
      this.delegate = smallView;

      int minimumTouchWidth = (int) (minWdith * ctx.getResources().getDisplayMetrics().density + 0.5f);
      int minimumTouchHeight = (int) (minHeight * ctx.getResources().getDisplayMetrics().density + 0.5f);

      Rect touchRect = new Rect();
      smallView.getHitRect(touchRect);
      int heightPadding = (minimumTouchHeight - touchRect.height()) / 2;
      int widthPadding = (minimumTouchWidth - touchRect.width()) / 2;

      this.topPadding = heightPadding;
      this.bottomPadding = heightPadding;
      this.leftPadding = widthPadding;
      this.rightPadding = widthPadding;
   }

   /**
    * Posted in the parent's message queue to make sure the parent lays out its children before we call getHitRect()
    */
   public void run()
   {
      View parent;
      try
      {
         parent = (View) delegate.getParent();
      }
      catch (ClassCastException e)
      {
         throw new IllegalArgumentException("Only Views with a View as parent can have touch area enlarged", e);
      }
      // Construct a new Rectangle and let the Delegate set its values
      Rect touchRect = new Rect();
      delegate.getHitRect(touchRect);

      // Modify the dimensions of the Rectangle
      // Padding values below zero are replaced by zeros
      touchRect.top -= Math.max(0, topPadding);
      touchRect.bottom += Math.max(0, bottomPadding);
      touchRect.left -= Math.max(0, leftPadding);
      touchRect.right += Math.max(0, rightPadding);

      // Now we are going to construct the TouchDelegate
      TouchDelegate touchDelegate = new TouchDelegate(touchRect, delegate);

      // And set it on the parent
      parent.setTouchDelegate(touchDelegate);
   }

   /**
    * Convenience method to initialize, connect and run the enlarger
    * 
    * @param ctx The context from which to retrieve the screen density information
    * @param smallView The view on which a alter the hitbox
    * @see #TouchDelegateAdjustment(Context, View)
    */
   static void adjustTouchSize(Context ctx, View smallView)
   {
      View parent = (View) smallView.getParent();
      parent.post(new TouchDelegateAdjustment(ctx, smallView));
   }
}