要素の大きさが固定であるなら、ScrollViewerの表示領域に表示されている要素は計算から調べられます。
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:app="clr-namespace:WpfApplication1"
Title="MainWindow" Height="350" Width="525">
<DockPanel>
<Button Content="TEST" DockPanel.Dock="Right" Click="Button_Click" />
<UniformGrid Columns="2">
<ScrollViewer HorizontalScrollBarVisibility="Disabled" Grid.Row="1" >
<WrapPanel x:Name="Wrp" Orientation="Horizontal" Loaded="Wrp_Loaded"/>
</ScrollViewer>
<ListBox x:Name="listBox1" ScrollViewer.VerticalScrollBarVisibility="Visible" ScrollViewer.HorizontalScrollBarVisibility="Disabled">
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<app:WrapPanelEx Orientation="Horizontal" />
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemTemplate>
<DataTemplate >
<Border Width="50" Height="50" Margin="5" >
<Image />
</Border>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</UniformGrid>
</DockPanel>
</Window>
Imports System.Collections.ObjectModel
Class MainWindow
Private Sub MainWindow_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
For i As Integer = 0 To 50
Dim b As New Border
b.Width = 50
b.Height = 50
b.Margin = New Thickness(10, 10, 0, 0)
Dim img As New Image
b.Child = img
'読み込ませたいURIを覚えさせておく
b.DataContext = New Uri("https://i1.social.s-msft.com/profile/u/avatar.jpg?displayname=quarterdeck")
Wrp.Children.Add(b)
Next
Me.listBox1.ItemsSource = collection
End Sub
Private Sub Wrp_Loaded(sender As Object, e As RoutedEventArgs)
WrapPanelEx.OnLoaded(sender, e)
End Sub
'コレクションで増減に反応させる
Dim collection As New ObservableCollection(Of Uri)
Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
For i As Integer = 0 To 10
collection.Add(New Uri("https://i1.social.s-msft.com/profile/u/avatar.jpg?displayname=quarterdeck"))
Next
End Sub
End Class
Class WrapPanelEx
Inherits WrapPanel
Public Shared Sub OnLoaded(sender As Object, e As RoutedEventArgs)
Dim wrap As WrapPanel = CType(sender, WrapPanel)
Dim d As DependencyObject = wrap
While (d IsNot Nothing)
Dim sv As ScrollViewer = TryCast(d, ScrollViewer)
If (sv IsNot Nothing) Then
sv.Tag = wrap
wrap.Tag = sv
AddHandler sv.ScrollChanged, AddressOf ScrollViewer_ScrollChanged
Return
End If
d = VisualTreeHelper.GetParent(d)
End While
End Sub
Private Shared Sub ScrollViewer_ScrollChanged(sender As Object, e As ScrollChangedEventArgs)
Changed(CType(sender, ScrollViewer))
End Sub
Private Shared Sub Changed(ByVal sv As ScrollViewer)
Dim wrap As WrapPanel = CType(sv.Tag, WrapPanel)
If (wrap.Children.Count = 0) Then
Return
End If
'ScrollViewerの表示領域に表示される要素を調べる
Dim w As Double = sv.ExtentWidth 'ScrollViewerの最大スクロール幅
Dim h As Double = sv.ExtentHeight 'ScrollViewerの最大スクロール高さ
Dim child As FrameworkElement = wrap.Children(0)
Dim childWidth As Double = (child.ActualWidth + child.Margin.Left + child.Margin.Right) '固定サイズの要素の幅(マージン含む)
Dim childHeight As Double = (child.ActualHeight + child.Margin.Top + child.Margin.Bottom) '固定サイズの要素の高さ(マージン含む)
Dim columnCount = sv.ViewportWidth \ childWidth '１行に表示される列数
'ScrollViewerの左上の要素のインデックス
Dim visibleStartIndex As Integer = CInt(Math.Floor(sv.VerticalOffset / childHeight)) * columnCount
'ScrollViewerの最後に表示されている要素のインデックス(見切れ含む)
Dim visibleEndIndex As Integer = CInt(Math.Floor((sv.VerticalOffset + sv.ViewportHeight) / childHeight)) * columnCount + (columnCount - 1)
visibleStartIndex = Math.Min(wrap.Children.Count - 1, visibleStartIndex)
visibleEndIndex = Math.Min(wrap.Children.Count - 1, visibleEndIndex)
OnScroll(wrap, visibleStartIndex, visibleEndIndex)
End Sub
Private Shared Sub OnScroll(ByVal wrp As WrapPanel, ByVal startIndex As Integer, ByVal endIndex As Integer)
If (startIndex >= 0) Then
For index As Integer = startIndex To endIndex
Dim child As FrameworkElement = wrp.Children(index)
If (child.Tag Is Nothing AndAlso TypeOf child.DataContext Is Uri) Then
child.Tag = True
Dim img As Image = FindChild(Of Image)(child)
If (img IsNot Nothing AndAlso img.Source Is Nothing) Then
'まだ読み込んでないなら読み込むImageをつくる
Dim bitmap As New BitmapImage()
Dim bnd As New Binding("DataContext")
bnd.Source = child
img.SetBinding(Image.SourceProperty, bnd)
End If
End If
Next
End If
End Sub
Private Shared Function FindChild(Of T As {DependencyObject})(ByVal p As DependencyObject) As T
Dim count = VisualTreeHelper.GetChildrenCount(p)
For i As Integer = 0 To count - 1
Dim child = VisualTreeHelper.GetChild(p, i)
If (TypeOf child Is T) Then
Return CType(child, T)
End If
child = FindChild(Of T)(child)
If child IsNot Nothing Then
Return CType(child, T)
End If
Next
Return Nothing
End Function
#Region "要素の追加削除に反応するように"
Sub New()
AddHandler Me.Loaded, AddressOf OnLoaded
End Sub
Private flag As Boolean
Private Sub OnVisualChildrenChangedDelay()
flag = False
Dim sv As ScrollViewer = TryCast(Me.Tag, ScrollViewer)
If (sv IsNot Nothing) Then
Changed(sv)
End If
End Sub
Protected Overrides Sub OnVisualChildrenChanged(visualAdded As DependencyObject, visualRemoved As DependencyObject)
MyBase.OnVisualChildrenChanged(visualAdded, visualRemoved)
If (Not flag) Then
flag = True
Dispatcher.BeginInvoke(New Action(AddressOf OnVisualChildrenChangedDelay), System.Windows.Threading.DispatcherPriority.Loaded)
End If
End Sub
#End Region
End Class
#Wrappanelの仮想化は大変なのです…
個別に明示されていない限りgekkaがフォーラムに投稿したコードにはフォーラム使用条件に基づき「MICROSOFT LIMITED PUBLIC LICENSE」が適用されます。(かなり自由に使ってOK!)
WrapControlで子要素が初めて画面に表示されたとき
