private TextBox tb;        public MainWindow()        {            InitializeComponent();        }        private void TextBox_LostFocus(object sender, RoutedEventArgs e)        {            tb = (TextBox)sender;            DoubleAnimation ta = new DoubleAnimation();            ta.From = 0.5;            ta.To = 0;            ta.Duration = new Duration(TimeSpan.FromMilliseconds(100));            Storyboard.SetTargetName(ta, "Opacity");            Storyboard.SetTargetProperty(ta, new PropertyPath(Border.OpacityProperty));            Storyboard storyBoard = new Storyboard();            storyBoard.Children.Add(ta);            this.RegisterName("Opacity", this.ColorFulBorder);            storyBoard.Begin(this, true);                    }        private void TextBox_GotFocus(object sender, RoutedEventArgs e)        {            double fleft, ftop, fwidth;            TextBox ntb = (TextBox)sender;            if (tb == null)            {                fleft = ntb.Margin.Left;                ftop = ntb.Margin.Top;                fwidth = ntb.Width;            }            else            {                //获得失去焦点的文本框的位置                fleft = tb.Margin.Left;                ftop = tb.Margin.Top;                fwidth = tb.Width;            }            //获得获得焦点的文本框的位置            double nleft = ntb.Margin.Left;            double ntop = ntb.Margin.Top;            double nwidth = ntb.Width;            //开启动画效果                        //ThicknessAnimation ta = new ThicknessAnimation();            SplineThicknessKeyFrame stk1 = new SplineThicknessKeyFrame();            SplineThicknessKeyFrame stk2 = new SplineThicknessKeyFrame();            ThicknessAnimationUsingKeyFrames du = new ThicknessAnimationUsingKeyFrames();                        stk1.Value = new Thickness(fleft, ftop, 0, 0);            stk2.Value = new Thickness(nleft, ntop, 0, 0);            stk1.KeyTime = KeyTime.FromTimeSpan(TimeSpan.FromMilliseconds(0));            stk2.KeyTime = KeyTime.FromTimeSpan(TimeSpan.FromMilliseconds(400));            stk2.KeySpline = new KeySpline(0, 0, 0, 1);            du.KeyFrames.Add(stk1);            du.KeyFrames.Add(stk2);            //ta.From = new Thickness(fleft,ftop,0,0);            //ta.To = new Thickness(nleft, ntop, 0, 0);            //ta.Duration = new Duration(TimeSpan.FromMilliseconds(200));            Storyboard.SetTargetName(du, "Margin");            Storyboard.SetTargetProperty(du, new PropertyPath(Border.MarginProperty));            Storyboard storyBoard = new Storyboard();            storyBoard.Children.Add(du);            this.RegisterName("Margin", this.ColorFulBorder);            DoubleAnimation ta = new DoubleAnimation();            ta.From = 0;            ta.To = 0.5;            ta.Duration = new Duration(TimeSpan.FromMilliseconds(100));            Storyboard.SetTargetName(ta, "Opacity");            Storyboard.SetTargetProperty(ta, new PropertyPath(Border.OpacityProperty));            Storyboard storyBoard2 = new Storyboard();            storyBoard2.Children.Add(ta);            this.RegisterName("Opacity", this.ColorFulBorder);            storyBoard2.Begin(this, true);            DoubleAnimation tw = new DoubleAnimation();            tw.From = fwidth;            tw.To = nwidth;            tw.Duration = new Duration(TimeSpan.FromMilliseconds(100));            Storyboard.SetTargetName(tw, "Width");            Storyboard.SetTargetProperty(tw, new PropertyPath(Border.WidthProperty));            Storyboard storyBoard3 = new Storyboard();            storyBoard3.Children.Add(tw);            this.RegisterName("Width", this.ColorFulBorder);            storyBoard3.Begin(this, true);            storyBoard.Begin(this, true);                    }

前台放个定义好的border，在文本框上绑定这俩个事件