扩展GridView控件——为内容项添加拖放及分组功能

引言

相信大家对GridView都不陌生,是非常有用的控件,用于平铺有序的显示多个内容项。打开任何WinRT应用或者是微软合作商的网站,都会在APP中发现GridView的使用。“Tiles”提供了一个简单易用,平铺方式来组织内容显示。Windows8的开始菜单是最典型的GridView 示例。“开始菜单”显示了系统中安装的所有应用程序,而且支持重新排列。

本文源于我们项目的开发人员,他们想在项目中提供与GridView相同的用户体验,想要创建类GridView控件。

GridView 可以显示大小不定的内容项,并且以有序的方式显示。如果各个内容项无序,并且内容尺寸大小相同,GirdView还支持拖拽操作。然而,这些功能并不是默认提供的,需要编写一定的代码才能实现。

本文主要介绍了扩展GridView控件——称为GridViewEx, GridViewEx主要实现GridView在不同大小的内容项中的拖拽功能。

背景

首先了解GridView的基本属性和功能,GridView包含一些属性集和 ItemTemplate。为了实现通过拖拽操作执行重排列功能,必须完成以下三件事:

1. 设置AllowDrop属性为true;

2. 设置CanReorderItems 属性值为True;

3. 绑定数据源,该数据源必须支持数据修改或支持重排序。例如,使用ObservableCollection或IList数据源。

<GridView ItemsSource="{Binding}" AllowDrop="True" CanReorderItems="True">
    <GridView.ItemTemplate>
        <DataTemplate>
            <Border BorderBrush="Aqua" BorderThickness="1" Background="Peru">
                <Grid Margin="12">
                    <Grid.RowDefinitions>
                        <RowDefinition />
                        <RowDefinition Height="Auto"/>
                    </Grid.RowDefinitions>
                    <TextBlock Text="{Binding}"/>
                    <TextBlock Grid.Row="1">item</TextBlock>
                </Grid>
            </Border>
        </DataTemplate>
    </GridView.ItemTemplate>
</GridView>

扩展后的GridView使用拖拽操作将会非常方便快捷。

GridViewEx 控件

GridViewEx控件弥补了GridView,功能如下:

  • 实现Item Panel 拖拽操作,而不是WrapGrid,StackPanel、VirtualizingStackPanel等
  • 分组时,实现拖拽功能;

我们也为GridViewEx增加了新建分组的功能,如果用户将内容项拖到控件左边或右边时会触发新建分组操作。

实现拖拽代码:

   1:  public class GridViewEx : GridView
   2:  {
   3:      /// <summary>
   4:      /// Initializes a new instance of the <see cref="GridViewEx"/> control.
   5:      /// </summary>
   6:      public GridViewEx()
   7:      {
   8:          // see attached sample
   9:      }
  10:   
  11:      private void GridViewEx_DragItemsStarting(object sender, DragItemsStartingEventArgs e)
  12:      {
  13:          // see attached sample
  14:      }
  15:   
  16:      /// <summary>
  17:      /// Stores dragged items into DragEventArgs.Data.Properties["Items"] value.
  18:      /// Override this method to set custom drag data if you need to.
  19:      /// </summary>
  20:      protected virtual void OnDragStarting(DragItemsStartingEventArgs e)
  21:      {
  22:          // see attached sample
  23:      }

该控件包含几个变量,用来存储拖放内容的索引。OnDragStarting 事件在DragEventArgs.Data.Properties[“Items”] 中存储拖拽的内容。OnDragStarting 需要根据自己的需求重写。

当用户拖拽某一项内容时,需要给用户提示来引导用户将内容放在合适的位置上。标准的GriView对象是通过滑动相邻的内实项来实现的。本文将在GridViewEx中完善此操作。

   1:  /// <summary>
   2:  /// Shows reoder hints while custom dragging.
   3:  /// </summary>
   4:  protected override void OnDragOver(DragEventArgs e)
   5:  {
   6:      // see attached sample }
   7:   
   8:  private int GetDragOverIndex(DragEventArgs e)
   9:  {
  10:      // see attached sample 
  11:  }

实现拖放代码

首先需要重写GridView.OnDrop方法,该方法会当用户释放某一项内容时触发。重写Ondrop方法,代码如下:

   1:  /// <summary>
   2:  /// Handles drag and drop for cases when it is not supported by the Windows.UI.Xaml.Controls.GridView control
   3:  /// </summary>
   4:  protected override async void OnDrop(DragEventArgs e)
   5:  {
   6:      // see attached sample
   7:  }

OnDrop方法主要实现了内容项从源分组移到目标分组的逻辑代码,以及创建新分组的功能。

添加新分组

如果GrideView通过IsSourceGrouped值为True来绑定CollectionViewSource情况下,GridView提供分组功能,这就意味着分组必须对数据源进行分组,但GridView没有访问数据的权限。因此本文在执行拖放操作时,实现添加新分组功能。GridViewEx.BeforeDrop事件处理此需求,并且提供更多的数据信息,如DragEventArgs数据。

当用户执行拖放操作时,触发BeforeDrop 事件。

   1:  /// <summary>
   2:  /// Occurs before performing drop operation,
   3:  /// </summary>
   4:  public event EventHandler<BeforeDropItemsEventArgs> BeforeDrop;
   5:  /// <summary>
   6:  /// Rises the <see cref="BeforeDrop"/> event.
   7:  /// </summary>
   8:  /// <param name="e">Event data for the event.</param>
   9:  protected virtual void OnBeforeDrop(BeforeDropItemsEventArgs e)
  10:  {
  11:      // see attached sample 
  12:  }

BeforeDropItemEventArgs包含关于被拖拽的内容项的重要信息,该信息在OnDrop事件中可使用的。

   1:  /// <summary>
   2:  /// Provides data for the <see cref="GridViewEx.BeforeDrop"/> event.
   3:  /// </summary>
   4:  public sealed class BeforeDropItemsEventArgs : System.ComponentModel.CancelEventArgs
   5:  {
   6:      /// <summary>
   7:      /// Gets the item which is being dragged.
   8:      /// </summary>
   9:      public object Item
  10:      {
  11:          get;
  12:      }
  13:      /// <summary>
  14:      /// Gets the current item index in the underlying data source.
  15:      /// </summary>
  16:      public int OldIndex
  17:      {
  18:          get;
  19:      }
  20:      /// <summary>
  21:      /// Gets the index in the underlying data source where
  22:      /// the item will be inserted by the drop operation.
  23:      /// </summary>
  24:      public int NewIndex
  25:      {
  26:          get;
  27:      }
  28:      /// <summary>
  29:      /// Gets the bool value determining whether end-user actions requested
  30:      /// creation of the new group in the underlying data source.
  31:      /// This property only makes sense if GridViewEx.IsGrouping property is true.
  32:      /// </summary>
  33:      /// <remarks>
  34:      /// If this property is true, create the new data group and insert it into
  35:      /// the groups collection at the positions, specified by the 
  36:      /// <see cref="BeforeDropItemsEventArgs.NewGroupIndex"/> property value.
  37:      /// Then the <see cref="GridViewEx"/> will insert dragged item
  38:      /// into the newly added group.
  39:      /// </remarks>
  40:      public bool RequestCreateNewGroup
  41:      {
  42:          get;
  43:      }
  44:      /// <summary>
  45:      /// Gets the current item data group index in the underlying data source.
  46:      /// This property only makes sense if GridViewEx.IsGrouping property is true.
  47:      /// </summary>
  48:      public int OldGroupIndex
  49:      {
  50:          get;
  51:      }
  52:      /// <summary>
  53:      /// Gets the data group index in the underlying data source
  54:      /// where the item will be inserted by the drop operation.
  55:      /// This property only makes sense if GridViewEx.IsGrouping property is true.
  56:      /// </summary>
  57:      public int NewGroupIndex
  58:      {
  59:          get;
  60:      }
  61:      /// <summary>
  62:      /// Gets the original <see cref="DragEventArgs"/> data. 
  63:      /// </summary>
  64:      public DragEventArgs DragEventArgs
  65:      {
  66:          get;
  67:      }
  68:  }

AllowNewGroup属性确定用户拖拽某一内容项到控件边界时,是否创建新组。GridView并没有提供此功能,在GridViewEX添加此功能。

   1:  /// <summary>
   2:  /// Gets or sets the value determining whether new group should be created at 
   3:  /// dragging the item to the empty space.
   4:  /// </summary>
   5:  public bool AllowNewGroup
   6:  {
   7:      get { return (bool)GetValue(AllowNewGroupProperty); }
   8:      set { SetValue(AllowNewGroupProperty, value); }
   9:  }
  10:   
  11:  /// <summary>
  12:  /// Identifies the <see cref="AllowNewGroup"/> dependency property.
  13:  /// </summary>
  14:  public static readonly DependencyProperty AllowNewGroupProperty =
  15:          DependencyProperty.Register("AllowNewGroup", typeof(bool), 
  16:          typeof(GridViewEx), new PropertyMetadata(false));

为了在拖拽过程中添加分组,需要将AllowNewGroup属性设置为True。处理GridViewEx.BeforeDrop事件,该事件的参数能够帮助决定单项内容的起始位置和目的位置。在BeforeDrop事件的Handler中,使用 NewGroupIndex 创建新的数据组,并插入到已有组集合。最后,需要实现的扩展GridView控件模板。在用户可拖拽的项目的位置创建新分组,并使用占位符来代替。一旦用户拖某一内容放置到控件的边界时,触发创建新分组,ItemsPresenter的两个边界元素是新组的占位符。

GridViewEx控件模板generic.xaml,如下:

   1:  <Style TargetType="local:GridViewEx">
   2:      <Setter Property="Padding" Value="0,0,0,10" />
   3:      <Setter Property="IsTabStop" Value="False" />
   4:      <Setter Property="TabNavigation" Value="Once" />
   5:      <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
   6:      <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Disabled"/>
   7:      <Setter Property="ScrollViewer.HorizontalScrollMode" Value="Enabled" />
   8:      <Setter Property="ScrollViewer.IsHorizontalRailEnabled" Value="False" />
   9:      <Setter Property="ScrollViewer.VerticalScrollMode" Value="Disabled" />
  10:      <Setter Property="ScrollViewer.IsVerticalRailEnabled" Value="False" />
  11:      <Setter Property="ScrollViewer.ZoomMode" Value="Disabled" />
  12:      <Setter Property="ScrollViewer.IsDeferredScrollingEnabled" Value="False" />
  13:      <Setter Property="ScrollViewer.BringIntoViewOnFocusChange" Value="True" />
  14:      <Setter Property="IsSwipeEnabled" Value="True" />
  15:      <Setter Property="Template">
  16:          <Setter.Value>
  17:              <ControlTemplate TargetType="local:GridViewEx">
  18:                  <Border BorderBrush="{TemplateBinding BorderBrush}"
  19:                          Background="{TemplateBinding Background}"
  20:                          BorderThickness="{TemplateBinding BorderThickness}">
  21:                      <ScrollViewer x:Name="ScrollViewer"
  22:                              TabNavigation="{TemplateBinding TabNavigation}"
  23:                              HorizontalScrollMode="
  24:                              {TemplateBinding ScrollViewer.HorizontalScrollMode}"
  25:                              HorizontalScrollBarVisibility=
  26:                                "{TemplateBinding 
  27:                                ScrollViewer.HorizontalScrollBarVisibility}"
  28:                              IsHorizontalScrollChainingEnabled=
  29:                                "{TemplateBinding 
  30:                                ScrollViewer.IsHorizontalScrollChainingEnabled}"
  31:                              VerticalScrollMode="
  32:                              {TemplateBinding ScrollViewer.VerticalScrollMode}"
  33:                              VerticalScrollBarVisibility=
  34:                                "{TemplateBinding 
  35:                                ScrollViewer.VerticalScrollBarVisibility}"
  36:                              IsVerticalScrollChainingEnabled=
  37:                                "{TemplateBinding 
  38:                                ScrollViewer.IsVerticalScrollChainingEnabled}"
  39:                              IsHorizontalRailEnabled="
  40:                              {TemplateBinding ScrollViewer.IsHorizontalRailEnabled}"
  41:                              IsVerticalRailEnabled="
  42:                              {TemplateBinding ScrollViewer.IsVerticalRailEnabled}"
  43:                              ZoomMode="{TemplateBinding 
  44:                              ScrollViewer.ZoomMode}"
  45:                              IsDeferredScrollingEnabled="
  46:                              {TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}"
  47:                              BringIntoViewOnFocusChange="
  48:                              {TemplateBinding ScrollViewer.BringIntoViewOnFocusChange}">
  49:                          <StackPanel Orientation="Horizontal">
  50:                              <Border Width="60" 
  51:                              x:Name="NewGroupPlaceHolderFirst" 
  52:                                      Background="Transparent" 
  53:                                      Padding="{TemplateBinding Padding}" 
  54:                                      Visibility="{Binding AllowNewGroup, 
  55:                                      Converter={StaticResource 
  56:                                        VisibilityConverter}, 
  57:                                        RelativeSource={RelativeSource TemplatedParent}}"/>
  58:                              <ItemsPresenter 
  59:                                  Header="{TemplateBinding Header}" 
  60:                                  HeaderTemplate="{TemplateBinding HeaderTemplate}"
  61:                                  HeaderTransitions="{TemplateBinding HeaderTransitions}"
  62:                                  Padding="{TemplateBinding Padding}"/>
  63:                              <Border Width="60" 
  64:                              x:Name="NewGroupPlaceHolderLast" 
  65:                                      Background="Transparent" 
  66:                                      Padding="{TemplateBinding Padding}" 
  67:                                      Visibility="{Binding AllowNewGroup, 
  68:                                      Converter={StaticResource 
  69:                                        VisibilityConverter}, 
  70:                                        RelativeSource={RelativeSource TemplatedParent}}"/>
  71:                          </StackPanel>
  72:                      </ScrollViewer>
  73:                  </Border>
  74:              </ControlTemplate>
  75:          </Setter.Value>
  76:      </Setter>
  77:  </Style>

丰富GridViewEx功能

如上所示,我们已经实现了基本的拖拽操作,与Windows8 开始菜单类似的功能,接下来讨论如何实现以下功能:

  • 尺寸大小不定的内容项
  • 分组
  • 添加新组
  • 节省跨会话布局空间

大小不定的内容项

Windows8展示了不同大小的Tiles,但是目前GridView或GridViewEx还不支持此功能。因为GridView使用WrapGrid作为默认的ItemsPanel,WrapPanel只能创建一种布局,即所有的条目尺寸相同的。因此微软提供了VariableSizedWrapGrid,支持不同大小块的布局创建。

GridViewEx控件的优势在于能够使用VariableSizedWrapGrid,并且很好的支持拖放操作。为了使用VariableSizedWrapGrid 并显示不同大小的内容项,必须实现以下功能:

将GridViewEx.ItemsPanel 设置为VariableSizedWrapGrid

在GridView中重写GridView 的PrepareContainerForItemOverride 方法。在该方法中,可以设置Item的RowSpan或ColumnSpan属性来识别内容项的大小。

即生成继承GridViewEx的新控件MyGridView。为什么需要扩展GridViewEx控件而不是重写GridViewEx的PrepareContainerForItemOverride方法?因为指定Item尺寸的逻辑必须放在数据模型中,而不是控件内部。

如想将某一项显示较大一点,需要在数据项中创建一个属性返回比1大的整型数值,来设置RowSpanhuoColumnSpan属性。

   1:  public class Item
   2:  {
   3:      public int Id { get; set; }
   4:      public int ItemSize { get; set; }
   5:      /* */
   6:  }

因此,当创建新的内容项,我们要指定ItemSize属性。如果值为1则表明常规尺寸,如果值为2则表明大尺寸,ColumnSpan属性则设置为2。

   1:  /// <summary>
   2:  /// This class sets VariableSizedWrapGrid.ColumnSpanProperty for GridViewItem controls, 
   3:  /// so that every item can have different size in the VariableSizedWrapGrid.
   4:  /// </summary>
   5:  public class MyGridView : GridViewSamples.Controls.GridViewEx
   6:  {
   7:      // set ColumnSpan according to the business logic
   8:      // (maybe some GridViewSamples.Samples.Item or group properties)
   9:      protected override void PrepareContainerForItemOverride(
  10:                Windows.UI.Xaml.DependencyObject element, object item)
  11:      {
  12:          try
  13:          {
  14:              GridViewSamples.Samples.Item it = item as GridViewSamples.Samples.Item;
  15:              if (it != null)
  16:              {
  17:                  element.SetValue(
  18:                    Windows.UI.Xaml.Controls.VariableSizedWrapGrid.ColumnSpanProperty, it.ItemSize);
  19:              }
  20:          }
  21:          catch
  22:          {
  23:              element.SetValue(Windows.UI.Xaml.Controls.VariableSizedWrapGrid.ColumnSpanProperty, 1);
  24:          }
  25:          finally
  26:          {
  27:              base.PrepareContainerForItemOverride(element, item);
  28:          }
  29:      }
  30:  }
创建MyGridView实例,并绑定到数据集合。

   1:  <local:MyGridView AllowDrop="True" CanReorderItems="True" 
   2:            CanDragItems="True" IsSwipeEnabled="True"
   3:            ItemsSource="{Binding}" 
   4:            ItemTemplate="{StaticResource ItemTemplate}" >
   5:      <GridView.ItemsPanel>
   6:          <ItemsPanelTemplate>
   7:              <VariableSizedWrapGrid ItemHeight="160" 
   8:              ItemWidth="160" />
   9:          </ItemsPanelTemplate>
  10:      </GridView.ItemsPanel>
  11:      <GridView.ItemContainerStyle>
  12:          <Style TargetType="GridViewItem">
  13:              <Setter Property="HorizontalContentAlignment" 
  14:              Value="Stretch"/>
  15:              <Setter Property="VerticalContentAlignment" 
  16:              Value="Stretch"/>
  17:          </Style>
  18:      </GridView.ItemContainerStyle>
  19:  </local:MyGridView>

如上所示,我们将指定内容项的ItemSize属性设置为2,效果如图所示:

分组

使用GridViewEx控件,能够实现添加新分组和拖拽等功能,也是在App中最为常见的功能,实现分组必须完成以下设置:

  • 为GridView绑定CollectionViewSource,必须使用支持分组的数据源。CollectionViewSource可视为代理服务器。
  • 使用GroupStyle确定分组结果如何显示,GroupStyle包含Header Tempate及Panel,因此需要指定子项目的排序方式。

在GridViewEx中添加支持不同大小的内容项,逻辑代码:

   1:  <local:MyGridView AllowDrop="True" CanReorderItems="True" 
   2:            CanDragItems="True" IsSwipeEnabled="True"
   3:            ItemsSource="{Binding}" 
   4:            ItemTemplate="{StaticResource ItemTemplate}" >
   5:      <GridView.ItemsPanel>
   6:          <ItemsPanelTemplate>
   7:              <VirtualizingStackPanel Orientation="Horizontal"/>
   8:          </ItemsPanelTemplate>
   9:      </GridView.ItemsPanel>
  10:      <GridView.GroupStyle>
  11:          <GroupStyle>
  12:              <GroupStyle.HeaderTemplate>
  13:                  <DataTemplate>
  14:                      <Grid Background="LightGray" 
  15:                      Margin="0">
  16:                          <TextBlock Foreground="Black" 
  17:                          Margin="10" 
  18:                                    Style="{StaticResource 
  19:                                    GroupHeaderTextStyle}">
  20:                              <Run Text="{Binding Id}"/>
  21:                              <Run Text=" group"/>
  22:                          </TextBlock>
  23:                      </Grid>
  24:                  </DataTemplate>
  25:              </GroupStyle.HeaderTemplate>
  26:   
  27:              <GroupStyle.ContainerStyle>
  28:                  <Style TargetType="GroupItem">
  29:                      <Setter Property="BorderBrush" 
  30:                      Value="DarkGray"/>
  31:                      <Setter Property="BorderThickness" 
  32:                      Value="2"/>
  33:                      <Setter Property="Margin" 
  34:                      Value="3,0"/>
  35:                  </Style>
  36:              </GroupStyle.ContainerStyle>
  37:   
  38:              <GroupStyle.Panel>
  39:                  <ItemsPanelTemplate>
  40:                      <VariableSizedWrapGrid ItemHeight="160" 
  41:                      ItemWidth="160" />
  42:                  </ItemsPanelTemplate>
  43:              </GroupStyle.Panel>
  44:          </GroupStyle>
  45:      </GridView.GroupStyle>
  46:   
  47:      <GridView.ItemContainerStyle>
  48:          <Style TargetType="GridViewItem">
  49:              <Setter Property="HorizontalContentAlignment" 
  50:              Value="Stretch"/>
  51:              <Setter Property="VerticalContentAlignment" 
  52:              Value="Stretch"/>
  53:          </Style>
  54:      </GridView.ItemContainerStyle>
  55:  </local:MyGridView>

运行演示:

添加新分组

自定义的GridViewEx控件支持新分组的创建,因此需要设置AllowNewGroup为True。其次处理添加新分组的数据层,处理GridViewEx.BeforeDrop 事件。

   1:  /// <summary>
   2:  /// Creates new CollectionViewSource and updates page DataContext.
   3:  /// </summary>
   4:  private void UpdateDataContext()
   5:  {
   6:      CollectionViewSource source = new CollectionViewSource();
   7:      source.Source = _groups;
   8:      source.ItemsPath = new PropertyPath("Items");
   9:      source.IsSourceGrouped = true;
  10:      this.DataContext = source;
  11:  }
  12:  // creates new group in the data source,
  13:  // if end-user drags item to the new group placeholder
  14:  private void MyGridView_BeforeDrop(object sender, Controls.BeforeDropItemsEventArgs e)
  15:  {
  16:      if (e.RequestCreateNewGroup)
  17:      {
  18:          // create new group and re-assign datasource 
  19:          Group group = Group.GetNewGroup();
  20:          if (e.NewGroupIndex == 0)
  21:          {
  22:              _groups.Insert(0, group);
  23:          }
  24:          else
  25:          {
  26:              _groups.Add(group);
  27:          }
  28:          UpdateDataContext();
  29:      }
  30:  }

也可以使用Drop事件删除空分组

   1:  // removes empty groups (except the last one)
   2:  private void MyGridView_Drop(object sender, DragEventArgs e)
   3:  {
   4:      bool needReset = false;
   5:      for (int i = _groups.Count - 1; i >= 0; i--)
   6:      {
   7:          if (_groups[i].Items.Count == 0 && _groups.Count > 1)
   8:          {
   9:              _groups.RemoveAt(i);
  10:              needReset = true;
  11:          }
  12:      }
  13:      if (needReset)
  14:      {
  15:          UpdateDataContext();
  16:      }
  17:  }

节省布局空间

Windows8支持挂起或终止功能,为了提供更好的用户体验,我们继续改善此前实现的功能,当用户离开当前页面,将当前的布局暂存。在本示例中,我们使用JSON 字符串简化数据序列化。根据已有的数据、数据的大小及需求,以其他格式来保存数据。我们主要将“业务对象集合”保存。

为了节省布局空间。重写LayoutAwarePage方法:

   1:  /// <summary>
   2:  /// Populates the page with content passed during navigation.  Any saved state is also
   3:  /// provided when recreating a page from a prior session.
   4:  /// </summary>
   5:  /// <param name="navigationParameter">The parameter value passed to
   6:  /// <see cref="Frame.Navigate(Type, 
   7:  /// Object)"/> when this page was initially requested.
   8:  /// </param>
   9:  /// <param name="pageState"
  10:  /// >A dictionary of state preserved by this page during an earlier
  11:  /// session.  This will be null the first time a page is visited.</param>
  12:  protected override void LoadState(Object navigationParameter, 
  13:      Dictionary<String, Object> pageState)
  14:  {
  15:      base.LoadState(navigationParameter, pageState);
  16:      if (pageState != null && pageState.Count > 0 
  17:      && pageState.ContainsKey("Groups"))
  18:      {
  19:          // restore groups and items from the previously serialized state
  20:          System.Runtime.Serialization.Json.DataContractJsonSerializer rootSer = 
  21:          new System.Runtime.Serialization.Json.DataContractJsonSerializer(typeof(List<Group>));
  22:          var stream = new MemoryStream(System.Text.Encoding.UTF8.GetBytes
  23:              ((string)pageState["Groups"]));
  24:          _groups = (List<Group>)rootSer.ReadObject(stream);
  25:      }
  26:      else
  27:      {
  28:          // if we get here for the first time and don't have
  29:          // serialized content, fill groups and items from scratch
  30:          for (int j = 1; j <= 12; j++)
  31:          {
  32:              Group group = Group.GetNewGroup();
  33:              for (int i = 1; i <= 7 + j % 3; i++)
  34:              {
  35:                  group.Items.Add(new Item()
  36:                  {
  37:                      Id = i,
  38:                      GroupId = group.Id
  39:                  });
  40:              }
  41:              _groups.Add(group);
  42:          }
  43:      }
  44:      UpdateDataContext();
  45:  }
  46:   
  47:  /// <summary>
  48:  /// Preserves state associated with this page in case the application is suspended or the
  49:  /// page is discarded from the navigation cache.  Values must conform to the serialization
  50:  /// requirements of <see cref="SuspensionManager.SessionState"/>.
  51:  /// </summary>
  52:  /// <param name="pageState">
  53:  /// An empty dictionary to be populated with serializable state.</param>
  54:  protected override void SaveState(Dictionary<String, Object> pageState)
  55:  {
  56:      // save groups and items to JSON string so that 
  57:      // it's possible to restore page state later
  58:      base.SaveState(pageState);
  59:      System.Runtime.Serialization.Json.DataContractJsonSerializer rootSer = 
  60:          new System.Runtime.Serialization.Json.DataContractJsonSerializer
  61:          (typeof(List<Group>));
  62:      var stream = new MemoryStream();
  63:      rootSer.WriteObject(stream, _groups);
  64:      string str = System.Text.Encoding.UTF8.GetString(stream.ToArray(), 
  65:              0, (int)stream.Length);
  66:      pageState.Add("Groups", str);
  67:  }
  68:   
  69:  /// <summary>
  70:  /// Invoked when this page is about to be displayed in a Frame.
  71:  /// </summary>
  72:  /// <param name="e">Event data that describes 
  73:  /// how this page was reached.  The Parameter
  74:  /// property is typically used to configure the page.</param>
  75:  protected override void OnNavigatedTo(NavigationEventArgs e)
  76:  {
  77:      // restore page state
  78:      var frameState = 
  79:      GridViewSamples.Common.SuspensionManager.SessionStateForFrame(this.Frame);
  80:      if (frameState.ContainsKey("TilePageData"))
  81:      {
  82:          this.LoadState(e.Parameter, 
  83:          (Dictionary<String, Object>)frameState["TilePageData"]);
  84:      }
  85:      else
  86:      {
  87:          this.LoadState(e.Parameter, null);
  88:      }
  89:  }
  90:   
  91:  protected override void OnNavigatedFrom(NavigationEventArgs e)
  92:  {
  93:      // save page state with "TilePageData" key
  94:      var frameState = 
  95:      GridViewSamples.Common.SuspensionManager.SessionStateForFrame(this.Frame);
  96:      var pageState = new Dictionary<String, Object>();
  97:      this.SaveState(pageState);
  98:      frameState["TilePageData"] = pageState;
  99:  }

GridViewEx控件丰富了GirdView控件功能,改进了基础功能,提升用户体验。到此已经实现了GridView项与Windows8开始菜单具有的相同用户体验,如果你想了解如何在Windows10平台下开发UWP引用,请持续关注下篇文章:如何在Windows10中开发UWP应用

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