WPF自定义控件之列表滑动特效 PowerListBox

列表控件是应用程序中常见的控件之一，对其做一些绚丽的视觉特效，可以让软件增色不少。

本人网上看过一个视频，是windows phone 7系统上的一个App的列表滚动效果，效果非常炫

现在在WPF上用ListBox重现此效果

首先我们来分析一下，这种实时滚动的效果是如何实现的，有哪些步骤

1.获取ListBox模板内部的ScrollViewer和ItemsPanel

2.监听ScrollViewer的滚动事件ScrollChange, 获取ItemsPanel的布局方向

3.在滚动事件发生时计算当前可视化区域中的第一项和最后一项，这是此滑动效果的核心算法所在，算法的效率决定了滑动效果的流畅性

4.根据滚动的方向和布局的方向依次对指定的Item做动画效果。

重写ListBoxItem

public class PowerListBoxItem : ListBoxItem

声明构造函数并赋初始值

        static PowerListBoxItem()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(PowerListBoxItem), new FrameworkPropertyMetadata(typeof(PowerListBoxItem)));
        }

        public PowerListBoxItem()
        {
            ItemStatus = ItemStatusEnum.Out;  //默认Item状态为"退出"
            duration = new TimeSpan(0, 0, 0, 0, 300);
            //easingFunction = new PowerEase() { EasingMode = EasingMode.EaseIn, Power = 4 };
            easingFunction = new CircleEase() { EasingMode = EasingMode.EaseInOut };
        }

定义PowerListBoxItem的成员属性

  　　　 /// <summary>
        /// PowerListBoxItem模板中的内容控件
        /// </summary>
        private FrameworkElement contentControl;

        /// <summary>
        /// 动画间隔时间
        /// </summary>
        private TimeSpan duration;

        private IEasingFunction easingFunction;   //动画缓动函数

        private IList<AnimationModel> DownInAnimationList;  //定义Item从下往上运动的动画内容集合

        private IList<AnimationModel> UpInAnimationList;    //定义Item从上往下运动的动画内容集合

        /// <summary>
        /// 项枚举状态，指明Item运动的方向
        /// </summary>
        internal enum ItemStatusEnum
        {
            UpIn, DownIn, RightIn, LeftIn, Out
        }

        private ItemStatusEnum _itemStatus;

        internal ItemStatusEnum ItemStatus
        {
            get { return _itemStatus; }
            set
            {
                if (_itemStatus == value)   //状态相同时不再刷新状态
                    return;
                _itemStatus = value;
                PlayAnimation(); //执行动画
            }
        }

重写ListBox

 [StyleTypedProperty(Property = "ItemContainerStyle", StyleTargetType = typeof(PowerListBoxItem))]
    public class PowerListBox : ListBox
    {
        static PowerListBox()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(PowerListBox), new FrameworkPropertyMetadata(typeof(PowerListBox)));
        }

        public PowerListBox()
        {
            DefaultStyleKey = typeof(PowerListBox);
        }
    }

     protected override DependencyObject GetContainerForItemOverride()
     {
       return new PowerListBoxItem();  //指定PowerListBox的项为PowerListBoxItem
     }

     protected override bool IsItemItsOwnContainerOverride(object item)
     {
        return item is PowerListBoxItem;
     }

定义PowerList的成员属性

 　　　  /// <summary>
        /// ListBox内部的滚动试图
        /// </summary>
        private ScrollViewer _scrollView;

        /// <summary>
        /// 容器的布局方向
        /// </summary>
        private Orientation _panelOrientation;

        /// <summary>
        /// 当前可视化视图的第一项
        /// </summary>
        private int firstVisibleIndex;

        /// <summary>
        /// 当前可视化视图的最后一项
        /// </summary>
        private int lastVisibleIndex;

        /// <summary>
        /// 上次滚动时可视化视图的第一项
        /// </summary>
        private int oldFirstVisibleIndex;

        /// <summary>
        /// 上次滚动时可视化视图的最后一项
        /// </summary>
        private int oldLastVisibleIndex;

        /// <summary>
        /// 标识，是否已找到第一项
        /// </summary>
        private bool isFindFirst;

        /// <summary>
        /// 当前累计已遍历过的Item高度或宽度的值，用于寻找第一项和最后一项
        /// </summary>
        private double cumulativeNum;

　获取PowerListBox内部的ScrollViewer和ItemsPanel，并监听滚动事件

        public override void OnApplyTemplate()
        {
            _scrollView = VisualHelper.FindFirstVisualChild<ScrollViewer>(this);
            if (_scrollView == null)
                return;
            _scrollView.CanContentScroll = false;  //不按Item为步长滚动
            _scrollView.PanningMode = PanningMode.Both;
            _scrollView.ScrollChanged += _scrollView_ScrollChanged;  //监听滚动事件

            var panel = this.ItemsPanel.LoadContent();  //读取布局容器
            if (panel is StackPanel)
                _panelOrientation = (panel as StackPanel).Orientation;
            else if (panel is VirtualizingPanel)
                _panelOrientation = (panel as VirtualizingStackPanel).Orientation;

            base.OnApplyTemplate();
        }

        private void _scrollView_ScrollChanged(object sender, ScrollChangedEventArgs e)
        {
            //Console.WriteLine("itemCount:{0}  VerticalOffset:{1}  ViewportHeight:{2}   ContentVerticalOffset:{3}",
            //Items.Count, _scrollView.VerticalOffset, _scrollView.ViewportHeight, _scrollView.ContentVerticalOffset);
            //每次滚动时都计算当前可视化区域的首尾项
            calculationIndex();
            refreshItemStatus(); //刷新Item状态
        }

计算可视化区域的第一项和最后一项

 　　　　private void calculationIndex()
        {
            oldFirstVisibleIndex = firstVisibleIndex;
            oldLastVisibleIndex = lastVisibleIndex;
            isFindFirst = false;
            if (_panelOrientation == Orientation.Vertical)
            {
                cumulativeNum = 0.0;
                for (int i = 0; i < Items.Count; i++)
                {
                    var _item = this.ItemContainerGenerator.ContainerFromIndex(i) as PowerListBoxItem;
                    cumulativeNum += _item.ActualHeight + _item.Margin.Top + _item.Margin.Bottom;
                    //遍历Items, 累计Item高度，第一个超过滚动条垂直偏移量的Item就是当前可视化区域中的第一项
                    if (!isFindFirst && cumulativeNum >= _scrollView.VerticalOffset)
                    {
                        firstVisibleIndex = i;
                        isFindFirst = true;
                    }

                    //累计Item高度超过滚动条垂直偏移量和滚动区显示高度的和，就是当前可视化区域的最后一项
                    if (cumulativeNum >= (_scrollView.VerticalOffset + _scrollView.ViewportHeight))
                    {
                        lastVisibleIndex = i;
                        break;
                    }
                }
            }
        }

确定当前可视化区域的首尾项之后，刷新Item的状态

 　　　　private void refreshItemStatus()
        {
            Console.WriteLine("firstIndex: {0}  lastIndex: {1}  oldFirstIndex: {2}  oldLastIndex: {3}  {4}",
                firstVisibleIndex, lastVisibleIndex, oldFirstVisibleIndex, oldLastVisibleIndex, firstVisibleIndex > oldFirstVisibleIndex ? "Down In" : firstVisibleIndex < oldFirstVisibleIndex ? "UpIn" : "normal");
            if ((firstVisibleIndex == oldFirstVisibleIndex && lastVisibleIndex == oldLastVisibleIndex) || oldFirstVisibleIndex == 0 && oldLastVisibleIndex == 0)
                return;
            //Console.WriteLine("firstVisibleIndex:{0} oldFirstVisibleIndex:{1}", firstVisibleIndex, oldFirstVisibleIndex);
            //判断滚动方向
            if (firstVisibleIndex > oldFirstVisibleIndex)
            {
                //垂直  滚动条往下，内容网上
                //水平  滚动条往右，内容往左
                for (var i = oldLastVisibleIndex; i <= lastVisibleIndex; i++)
                {
                    var _item = this.ItemContainerGenerator.ContainerFromIndex(i) as PowerListBoxItem;
                    _item.ItemStatus = _panelOrientation == Orientation.Vertical ? PowerListBoxItem.ItemStatusEnum.DownIn : PowerListBoxItem.ItemStatusEnum.RightIn;
                    //Console.WriteLine("DownIn {0}", i);
                }
            }
            else if (lastVisibleIndex < oldLastVisibleIndex)
            {
                //垂直  滚动条往上，内容网下
                //水平  滚动条往左，内容往右
                for (var i = oldFirstVisibleIndex; i >= firstVisibleIndex; i--)
                {
                    var _item = this.ItemContainerGenerator.ContainerFromIndex(i) as PowerListBoxItem;
                    _item.ItemStatus = _panelOrientation == Orientation.Vertical ? PowerListBoxItem.ItemStatusEnum.UpIn : PowerListBoxItem.ItemStatusEnum.LeftIn;
                    //Console.WriteLine("UpIn {0}", i);
                }
            }
        }

定义PowerListBox的默认外观

 <Style TargetType="{x:Type local:PowerListBox}">
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="BorderBrush" Value="Transparent"/>
        <Setter Property="Padding" Value="0"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:PowerListBox}">
                    <ScrollViewer x:Name="ScrollViewer" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Foreground="{TemplateBinding Foreground}" Padding="{TemplateBinding Padding}">
                        <ItemsPresenter/>
                    </ScrollViewer>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style TargetType="{x:Type local:PowerListBoxItem}">
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="BorderBrush" Value="Transparent"/>
        <Setter Property="Padding" Value="0"/>
        <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
        <Setter Property="VerticalContentAlignment" Value="Stretch"/>
        <Setter Property="Margin" Value="0,8"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:PowerListBoxItem}">
                    <Border x:Name="LayoutRoot" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" HorizontalAlignment="{TemplateBinding HorizontalAlignment}" VerticalAlignment="{TemplateBinding VerticalAlignment}">
                        <ContentControl x:Name="ContentContainer" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}"
                                            Foreground="{TemplateBinding Foreground}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}"
                                            VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" RenderTransformOrigin="0.5,0.5">
                            <ContentControl.RenderTransform>
                                <TransformGroup>
                                    <TranslateTransform/>
                                </TransformGroup>
                            </ContentControl.RenderTransform>
                        </ContentControl>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

调用 PowerListBox

 <local:PowerListBox ItemsSource="{Binding TestModelList}" >
          <local:PowerListBox.ItemTemplate>
                  <DataTemplate>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="150"/>
                                    <ColumnDefinition/>
                                </Grid.ColumnDefinitions>
                                <TextBlock Text="{Binding Name}" VerticalAlignment="Center" FontSize="20"/>
                                <Border Width="100" Height="120" Background="#FF4949D3" Grid.Column="1" HorizontalAlignment="Left">
                                    <TextBlock Text="{Binding Id}" VerticalAlignment="Center" HorizontalAlignment="Center" FontSize="40" Foreground="Black"/>
                                </Border>
                            </Grid>
                 </DataTemplate>
        </local:PowerListBox.ItemTemplate>
</local:PowerListBox>

效果图　　

由于gif录制帧数的原因，效果图不是很流畅，但实际运行情况动画效果是非常流畅的