Creating checkboxes with bigger touch targets

CheckBoxHelper.java

import android.graphics.Rect;
import android.view.View;
import android.widget.CheckBox;

/**
 * Enlarges the effective hit target of a checkbox to more closely match the dimensions of the
 * provided root view.  If the provided root isn't actually an ancestor view of the checkbox, bad
 * things will happen.
 * <p/>
 * See: http://developer.android.com/training/gestures/viewgroup.html#delegate
 */
public class CheckBoxHelper {
    public static void enlargeCheckBoxHitTarget(final View rootView, final CheckBox checkBox) {
        rootView.post(new Runnable() {
            @Override
            public void run() {
                int relativeCheckTop = ViewHelper.getRelativeTop(rootView, checkBox);
                int relativeCheckBottom = ViewHelper.getRelativeBottom(rootView, checkBox);
                int relativeCheckLeft = ViewHelper.getRelativeLeft(rootView, checkBox);

                int additionalTop = relativeCheckTop;
                int additionalBottom = rootView.getMeasuredHeight() - relativeCheckBottom;
                int additionalLeft = relativeCheckLeft;
                // Semi-arbitrary, right is same as left.  Makes sense when a checkbox is on the left.
                int additionalRight = additionalLeft;

                setLargerHitTarget(checkBox, additionalLeft, additionalTop, additionalRight, additionalBottom);
            }
        });
    }

    private static void setLargerHitTarget(View view, int additionalLeft, int additionalTop, int additionalRight, int additionalBottom) {
        Rect origHitRect = new Rect();
        view.getHitRect(origHitRect);

        Rect delegateHitRect = new Rect(
                origHitRect.left - additionalLeft,
                origHitRect.top - additionalTop,
                origHitRect.right + additionalRight,
                origHitRect.bottom + additionalBottom);

        HackedTouchDelegate touchDelegate = new HackedTouchDelegate(delegateHitRect, view);
        if (View.class.isInstance(view.getParent())) {
            ((View) view.getParent()).setTouchDelegate(touchDelegate);
        }
    }
}

HackedTouchDelegate.java

import android.graphics.Rect;
import android.view.MotionEvent;
import android.view.TouchDelegate;
import android.view.View;
import android.view.ViewConfiguration;

/**
 * There is a bug with TouchDelegate where ancestor views can get into an awkward state after
 * a delegate view has been actioned upon by the touch delegate.
 *
 * This class is a direct copy of https://github.com/android/platform_frameworks_base/blob/master/core/java/android/view/TouchDelegate.java
 * but with the fix.
 *
 * See: https://code.google.com/p/android/issues/detail?id=36445 for details.
 */
public class HackedTouchDelegate extends TouchDelegate {
    /**
     * View that should receive forwarded touch events
     */
    private View mDelegateView;

    /**
     * Bounds in local coordinates of the containing view that should be mapped to the delegate
     * view. This rect is used for initial hit testing.
     */
    private Rect mBounds;

    /**
     * mBounds inflated to include some slop. This rect is to track whether the motion events
     * should be considered to be be within the delegate view.
     */
    private Rect mSlopBounds;

    /**
     * True if the delegate had been targeted on a down event (intersected mBounds).
     */
    private boolean mDelegateTargeted;

    /**
     * The touchable region of the View extends above its actual extent.
     */
    public static final int ABOVE = 1;

    /**
     * The touchable region of the View extends below its actual extent.
     */
    public static final int BELOW = 2;

    /**
     * The touchable region of the View extends to the left of its
     * actual extent.
     */
    public static final int TO_LEFT = 4;

    /**
     * The touchable region of the View extends to the right of its
     * actual extent.
     */
    public static final int TO_RIGHT = 8;

    private int mSlop;

    /**
     * Constructor
     *
     * @param bounds Bounds in local coordinates of the containing view that should be mapped to
     *        the delegate view
     * @param delegateView The view that should receive motion events
     */
    public HackedTouchDelegate(Rect bounds, View delegateView) {
        super(bounds, delegateView); // Doesn't actually matter since we are overriding the entire implementation

        mBounds = bounds;

        mSlop = ViewConfiguration.get(delegateView.getContext()).getScaledTouchSlop();
        mSlopBounds = new Rect(bounds);
        mSlopBounds.inset(-mSlop, -mSlop);
        mDelegateView = delegateView;
    }

    /**
     * Will forward touch events to the delegate view if the event is within the bounds
     * specified in the constructor.
     *
     * @param event The touch event to forward
     * @return True if the event was forwarded to the delegate, false otherwise.
     */
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int)event.getX();
        int y = (int)event.getY();
        boolean sendToDelegate = false;
        boolean hit = true;
        boolean handled = false;

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Rect bounds = mBounds;

                if (bounds.contains(x, y)) {
                    mDelegateTargeted = true;
                    sendToDelegate = true;
                } else { // NOTE: This else block reflects the only effective change to this class.
                    mDelegateTargeted = false;
                    sendToDelegate = false;
                }
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_MOVE:
                sendToDelegate = mDelegateTargeted;
                if (sendToDelegate) {
                    Rect slopBounds = mSlopBounds;
                    if (!slopBounds.contains(x, y)) {
                        hit = false;
                    }
                }
                break;
            case MotionEvent.ACTION_CANCEL:
                sendToDelegate = mDelegateTargeted;
                mDelegateTargeted = false;
                break;
        }
        if (sendToDelegate) {
            final View delegateView = mDelegateView;

            if (hit) {
                // Offset event coordinates to be inside the target view
                event.setLocation(delegateView.getWidth() / 2, delegateView.getHeight() / 2);
            } else {
                // Offset event coordinates to be outside the target view (in case it does
                // something like tracking pressed state)
                int slop = mSlop;
                event.setLocation(-(slop * 2), -(slop * 2));
            }
            handled = delegateView.dispatchTouchEvent(event);
        }
        return handled;
    }
}

impact.txt

Before (white space around the checkbox is not touchable):
 ____________________
|                    |
|  [.]  Lorem ipsum  |
|____________________|


After (dots around the checkbox are touchable):
 ____________________
|.......             |
|..[.]..Lorem ipsum  |
|......._____________|

usage.java

View convertView = // for example, something from an adapter
CheckBox checkBox = // a checkbox that exists inside of convertview
CheckBoxHelper.enlargeCheckBoxHitTarget(convertView, checkBox);

ViewHelper.java

import android.view.View;

public class ViewHelper {
    /**
     * Similar to View.getLeft(), but you specify what parent the value is relative to.  If you
     * provide a root view that isn't actually an ancestor view, bad things will happen.
     */
    public static int getRelativeLeft(View relativeRootView, View view) {
        int[] viewLocation = new int[2];
        view.getLocationInWindow(viewLocation);

        int[] rootLocation = new int[2];
        relativeRootView.getLocationInWindow(rootLocation);

        return viewLocation[0] - rootLocation[0];
    }

    /**
     * Similar to View.getTop(), but you specify what parent the value is relative to.  If you
     * provide a root view that isn't actually an ancestor view, bad things will happen.
     */
    public static int getRelativeTop(View relativeRootView, View view) {
        int[] viewLocation = new int[2];
        view.getLocationInWindow(viewLocation);

        int[] rootLocation = new int[2];
        relativeRootView.getLocationInWindow(rootLocation);

        return viewLocation[1] - rootLocation[1];
    }

    /**
     * Similar to View.getRight(), but you specify what parent the value is relative to.  If you
     * provide a root view that isn't actually an ancestor view, bad things will happen.
     */
    public static int getRelativeRight(View relativeRootView, View view) {
        return getRelativeLeft(relativeRootView, view) + view.getMeasuredWidth();
    }

    /**
     * Similar to View.getBottom(), but you specify what parent the value is relative to.  If you
     * provide a root view that isn't actually an ancestor view, bad things will happen.
     */
    public static int getRelativeBottom(View relativeRootView, View view) {
        return getRelativeTop(relativeRootView, view) + view.getMeasuredHeight();
    }
}