mono touch中处理视图过长，输入框被键盘遮挡的问题

需要对输入框进行监听，然后用动画将当期视图进行上移.

NSNotificationCenter.DefaultCenter.AddObserver (UITextView.TextDidBeginEditingNotification, (notity) => {
				InvokeOnMainThread (() => {
					//Tools.Alert ("do");
					UIView.BeginAnimations ("answerviewanimation2");
					this.View.Center = new PointF (rf.Width / 2, rf.Height / 2 - 215);
					UIView.CommitAnimations ();
				});
			});

/// <summary>
		/// 隐藏键盘
		/// </summary>
		public override void TouchesBegan (NSSet touches, UIEvent evt)
		{
			base.TouchesBegan (touches, evt);
			UITouch touch = touches.AnyObject as UITouch;
			if (touch != null) {
				if (!utxt.Frame.Contains (touch.LocationInView (this.View))) {
					utxt.ResignFirstResponder ();
					//视图下移
					UIView.BeginAnimations ("answerviewanimation2");
					float _t = Tools.IsSdk7 () ? 0 : 44;
					this.View.Center = new PointF (rf.Width / 2, (rf.Height + 44) / 2 - _t);
					UIView.CommitAnimations ();
				}
			}
		}