Wpf跑马灯——Storyboard运用

本文将建立一个wpf项目中运用Storyboard描述出一个跑马灯效果的简单实例，以下是详细步骤：

---

新建一个wpf项目，添加演示用图片，修改图片属性为"如果较新则复制"。

---

在MainWindow.xaml中，为系统自动创建的Grid容器命名，这样可以在后台操作的到它。

<Window x:Class="WpfRollPic.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" Loaded="Window_Loaded">
    <Grid Name="grid_main"></Grid>
</Window>

---

在后台代码中，添加窗体布局。

 public MainWindow()
        {
            InitializeComponent();
            this.GridLayout();
        }

        Canvas canvas_board = new Canvas();
        Image image1 = new Image();
        Image image2 = new Image();

        void GridLayout()
        {
            this.WindowStartupLocation = WindowStartupLocation.CenterScreen;
            this.Width = 300;
            this.Height = 300;

            canvas_board.VerticalAlignment = VerticalAlignment.Top;
            canvas_board.HorizontalAlignment = HorizontalAlignment.Left;
            canvas_board.Margin = new Thickness(10, 10, 0, 0);
            canvas_board.Width = 200;
            canvas_board.Height = 200;
            //canvas_board.Background = new SolidColorBrush(Colors.LightBlue);
            canvas_board.ClipToBounds = true;
            this.grid_main.Children.Add(canvas_board);

            image1.Stretch = Stretch.Fill;
            image1.Width = 200;
            image1.Height = 200;
            this.canvas_board.Children.Add(image1);
            image1.SetValue(Canvas.TopProperty, 0.0);
            image1.SetValue(Canvas.LeftProperty, 0.0);

            image2.Stretch = Stretch.Fill;
            image2.Width = 200;
            image2.Height = 200;
            this.canvas_board.Children.Add(image2);
            image2.SetValue(Canvas.TopProperty, 200.0);
            image2.SetValue(Canvas.LeftProperty, 0.0);
        }

注意这里需要设置Canvas控件的ClipToBounds属性为true，这样Canvas将不再显示出超出自己范围以外的内容。同时使用到了SetValue方法来设置Image控件的Canvas.Top/Canvas.Left属性。

---

添加初始化函数，代码如下：

        List<BitmapImage> ls_images = new List<BitmapImage>(); //存放图片组
        int n_index = 0;    //滚动索引
        double n_height;   //滚动高度

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            string[] img_files = Directory.GetFiles(string.Format("{0}/Images", AppDomain.CurrentDomain.SetupInformation.ApplicationBase), "*.png");
            foreach (string img_path in img_files)
            {
                ls_images.Add(new BitmapImage(new Uri(img_path, UriKind.Absolute)));
            }
            n_height = this.canvas_board.Height;
            this.image1.Source = ls_images[n_index++ % ls_images.Count];
            this.image2.Source = ls_images[n_index % ls_images.Count];

            this.StoryLoad();
        }

这里完成了一些图片素材的初始化，下面还需要完成故事板StoryLoad初始化事件：

        Storyboard storyboard_imgs = new Storyboard();

        void StoryLoad()
        {
            DoubleAnimationUsingKeyFrames daukf_img1 = new DoubleAnimationUsingKeyFrames();
            LinearDoubleKeyFrame k1_img1 = new LinearDoubleKeyFrame(0.0, KeyTime.FromTimeSpan(TimeSpan.FromSeconds(2)));
            LinearDoubleKeyFrame k2_img1 = new LinearDoubleKeyFrame(-n_height, KeyTime.FromTimeSpan(TimeSpan.FromSeconds(4)));
            daukf_img1.KeyFrames.Add(k1_img1);
            daukf_img1.KeyFrames.Add(k2_img1);
            storyboard_imgs.Children.Add(daukf_img1);
            Storyboard.SetTarget(daukf_img1, image1);
            Storyboard.SetTargetProperty(daukf_img1, new PropertyPath("(Canvas.Top)"));

            DoubleAnimationUsingKeyFrames daukf_img2 = new DoubleAnimationUsingKeyFrames();
            LinearDoubleKeyFrame k1_img2 = new LinearDoubleKeyFrame(n_height, KeyTime.FromTimeSpan(TimeSpan.FromSeconds(2)));
            LinearDoubleKeyFrame k2_img2 = new LinearDoubleKeyFrame(0.0, KeyTime.FromTimeSpan(TimeSpan.FromSeconds(4)));
            daukf_img2.KeyFrames.Add(k1_img2);
            daukf_img2.KeyFrames.Add(k2_img2);
            storyboard_imgs.Children.Add(daukf_img2);
            Storyboard.SetTarget(daukf_img2, image2);
            Storyboard.SetTargetProperty(daukf_img2, new PropertyPath("(Canvas.Top)"));

            storyboard_imgs.FillBehavior = FillBehavior.Stop;
            storyboard_imgs.Completed += new EventHandler(storyboard_imgs_Completed);
            storyboard_imgs.Begin();
        }

注意到添加了关键帧，

关键帧1：实现跑马灯图片停顿的效果，可以按照需求设置关键帧的时长就是停顿的时长；

关键帧2：实现跑马灯的滚动效果，可以设置关键帧的时长就是滚动一次所需时间；

注意到这里必须设置故事板storyboard_imgs的FillBehavior属性为Stop，这样在一个故事结束后，所有与故事相关联的属性将可以回到初始状态。

下面完成故事板storyboard_imgs的完成Completed事件，代码如下：

        void storyboard_imgs_Completed(object sender, EventArgs e)
        {
            image1.SetValue(Canvas.TopProperty, 0.0);
            image2.SetValue(Canvas.TopProperty, n_height);
            image1.Source = ls_images[n_index++ % ls_images.Count];
            image2.Source = ls_images[n_index % ls_images.Count];
            storyboard_imgs.Begin();
        }

Completed事件中，更改了image1和image2的图片，这样看起来，改变图片和位置的image1就好像变成了之前的image2，从而达到跑马灯的效果。

---

重新生成项目，F5运行，效果如下: