Android 获取NavigationBar高度

使用方法如下：

Point point = getNavigationBarSize(this);
bottomHeight = point.y;
 if (bottomHeight > 0) {
     //有NavigationBar
 }

public static Point getNavigationBarSize(Context context) {
        Point appUsableSize = getAppUsableScreenSize(context);
        Point realScreenSize = getRealScreenSize(context);

        // navigation bar on the right
        if (appUsableSize.x < realScreenSize.x) {
            return new Point(realScreenSize.x - appUsableSize.x, appUsableSize.y);
        }

        // navigation bar at the bottom
        if (appUsableSize.y < realScreenSize.y) {
            return new Point(appUsableSize.x, realScreenSize.y - appUsableSize.y);
        }

        // navigation bar is not present
        return new Point();
    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
    public static Point getAppUsableScreenSize(Context context) {
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        Display display = windowManager.getDefaultDisplay();
        Point size = new Point();
        display.getSize(size);
        return size;
    }

    public static Point getRealScreenSize(Context context) {
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        Display display = windowManager.getDefaultDisplay();
        Point size = new Point();

        if (Build.VERSION.SDK_INT >= 17) {
            display.getRealSize(size);
        } else if (Build.VERSION.SDK_INT >= 14) {
            try {
                size.x = (Integer) Display.class.getMethod("getRawWidth").invoke(display);
                size.y = (Integer) Display.class.getMethod("getRawHeight").invoke(display);
            } catch (IllegalAccessException e) {
            } catch (InvocationTargetException e) {
            } catch (NoSuchMethodException e) {
            }
        }

        return size;
    }