扩展GridView控件——为内容项添加拖放及分组功能

来源:互联网 时间:1970-01-01

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: }

总结

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

原文链接:http://www.codeproject.com/Articles/536519/Extending-GridView-with-Drag-and-Drop-for-Grouping


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