WPF项控件不会自动显示VerticalScrollBar

Question

这是意图，

当项目被添加到ItemsControl并且内容超过可用大小时，我希望看到在ItemsControl中滚动。我敢打赌这是任何ItemsControl类型的默认行为。

所以我生成了一个样本复制了我的意图。建议我需要解决的问题

<StackPanel>
        <StackPanel.Resources>
            <Style TargetType="{x:Type ItemsControl}">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="{x:Type ItemsControl}">
                            <Border SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}">
                                <ScrollViewer VerticalScrollBarVisibility="Visible">
                                    <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                </ScrollViewer>
                            </Border>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </StackPanel.Resources>
        <ToggleButton Name="SomeToggle" Content="Show/Hide"/>
        <Button Content="Add Item" Click="ButtonBase_OnClick" />
        <TextBlock Text="Hide/Show on toggle" >
            <TextBlock.Style>
                <Style TargetType="TextBlock">
                    <Setter Property="Visibility" Value="Collapsed"/>
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding Path=IsChecked,ElementName=SomeToggle}" Value="True">
                            <Setter Property="Visibility" Value="Visible" />
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </TextBlock.Style>
        </TextBlock>

    <ItemsControl Name="ItemsCollection" >
    </ItemsControl>

</StackPanel>

和代码背后：

private int counter = 0;
    private ObservableCollection<string> coll; 
    public MainWindow()
    {
        coll= new ObservableCollection<string>();
        //ItemsCollection.ItemsSource = coll;
        InitializeComponent();
    }

    private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
    {
        ItemsCollection.Items.Add(string.Format("Item {0}", ++counter));
    }

Answer 1

每次将ScrollViewer放入Stackpanel时，基本上会发生这种情况，这是由于Stackpanel的工作方式，看看Liskov Substitution Principle

您可以将Stackpanel放在ScrollView内，或者更好地将主面板更改为Grid

   <Grid >
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="Auto"/>            
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
    <Grid.Resources>
        <Style TargetType="{x:Type ItemsControl}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ItemsControl}">
                        <Border SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}">
                            <ScrollViewer VerticalScrollBarVisibility="Visible">
                                <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </ScrollViewer>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Grid.Resources>
    <ToggleButton Name="SomeToggle" Content="Show/Hide" Grid.Row="0"/>
    <Button Content="Add Item" Click="ButtonBase_OnClick" Grid.Row="1"/>
    <TextBlock Text="Hide/Show on toggle" Grid.Row="2">
        <TextBlock.Style>
            <Style TargetType="TextBlock">
                <Setter Property="Visibility" Value="Collapsed"/>
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=IsChecked,ElementName=SomeToggle}" Value="True">
                        <Setter Property="Visibility" Value="Visible" />
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </TextBlock.Style>
    </TextBlock>
    <ItemsControl Name="ItemsCollection" Grid.Row="3">
    </ItemsControl>
</Grid>

Answer 2

您无法看到滚动条的唯一原因是您没有设置ItemsControl的高度。

每次添加项目时，它的高度都会扩展，StackPanel会随之扩展以包含内容。您已经将ScrollViewer定义为ItemsControl模板，您还必须决定它必须在什么时候工作。

<ItemsControl Name="ItemsCollection" Height="200" >
</ItemsControl>

然后，在StackPanel中包含它或任何其他控件也无关紧要。

初始滚动条

添加项目后

代码

仅从理解的角度来看。这也可以：

删除项目控制的样式＆amp;设置滚动查看器的高度。

处理所有元素的高度：

<ScrollViewer MaxHeight="{Binding RelativeSource={RelativeSource AncestorType={x:Type Border}},Path=ActualHeight,Mode=OneWay}">
    <StackPanel>
    <StackPanel.Resources>
        <Style TargetType="{x:Type ItemsControl}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ItemsControl}">
                        <Border SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}">
                            <ScrollViewer VerticalScrollBarVisibility="Visible">
                                <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </ScrollViewer>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </StackPanel.Resources>
    <ToggleButton Name="SomeToggle" Content="Show/Hide"/>
    <Button Content="Add Item" Click="Button_Click" />
    <TextBlock Text="Hide/Show on toggle" >
        <TextBlock.Style>
            <Style TargetType="TextBlock">
                <Setter Property="Visibility" Value="Collapsed"/>
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=IsChecked,ElementName=SomeToggle}" Value="True">
                        <Setter Property="Visibility" Value="Visible" />
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </TextBlock.Style>
    </TextBlock>

    <ItemsControl Name="ItemsCollection" ItemsSource="{Binding list}" 
                  MaxHeight="{Binding RelativeSource={RelativeSource AncestorType={x:Type Border}},Path=ActualHeight,Mode=OneWay}">
    </ItemsControl>

</StackPanel>
</ScrollViewer>