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。
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控件弥补了GridView，功能如下：
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。
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: }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。
如果GrideView通过将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>
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：
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：
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：
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：
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: }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
原文链接：http://www.codeproject.com/Articles/536519/Extending-GridView-with-Drag-and-Drop-for-Grouping
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