在现代用户界面设计中，动态调整布局以适应不同数量的项目是一个常见的需求。例如，当一个列表控件中只有一个项目时，希望这个项目能够占据整个屏幕空间。本文将介绍如何通过XAML和C#代码实现这种动态布局调整。
首先，定义了一个DataTemplate，它包含了一个Expander控件，该控件用于展开和折叠子项列表。这个Expander控件的背景设置为透明，并且默认是展开的。
<DataTemplate DataType="{x:Type local:EmbeddedViewModel}">
<Expander x:Name="exp" Background="Transparent" IsExpanded="True" ExpandDirection="Down">
<ListView ...>
<ListView.View>
<GridView>
<GridViewColumn Width="100" Header="FieldA" DisplayMemberBinding="{Binding FieldA}"/>
<GridViewColumn Width="100" Header="FieldB" DisplayMemberBinding="{Binding FieldB}"/>
</GridView>
</ListView.View>
</ListView>
</Expander>
</DataTemplate>
接下来，创建了一个ItemsControl，它使用了一个特殊的Grid控件作为其ItemsPanelTemplate。这个特殊的Grid控件会在添加新的VisualChild时触发一个事件。
<ItemsControl x:Name="items" ItemsSource="{Binding Path=Items, Mode=OneWay}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<local:GridWithChildChangedNoitfication ... />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate DataType="{x:Type local:EmbeddedViewModel}">
...
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
在C#代码中，定义了一个名为GridWithChildChangedNoitfication的类，它继承自Grid。这个类重写了OnVisualChildrenChanged方法，并在添加或移除VisualChild时触发一个事件。
public class GridWithChildChangedNoitfication : Grid
{
protected override void OnVisualChildrenChanged(DependencyObject visualAdded, DependencyObject visualRemoved)
{
base.OnVisualChildrenChanged(visualAdded, visualRemoved);
OnGridVisualChildrenChanged(EventArgs.Empty);
}
public event EventHandler GridVisualChildrenChanged;
protected virtual void OnGridVisualChildrenChanged(EventArgs e)
{
EventHandler handler = GridVisualChildrenChanged;
handler?.Invoke(this, e);
}
}
public partial class Window1 : Window
{
private GridWithChildChangedNoitfication itemsGrid;
public Window1()
{
InitializeComponent();
this.DataContext = new Window1ViewModel();
this.Unloaded += ViewUnloaded;
}
private void ViewUnloaded(object sender, RoutedEventArgs e)
{
if (itemsGrid != null)
{
itemsGrid.GridVisualChildrenChanged -= GridChildrenChanged;
}
}
private void GridChildrenChanged(object sender, EventArgs e)
{
ResizeRows();
}
private void ResizeRows()
{
if (itemsGrid != null)
{
itemsGrid.RowDefinitions.Clear();
for (int i = 0; i < itemsGrid.Children.Count; i++)
{
RowDefinition row = new RowDefinition();
row.Height = new GridLength(itemsGrid.ActualHeight / itemsGrid.Children.Count, GridUnitType.Pixel);
itemsGrid.RowDefinitions.Add(row);
itemsGrid.Children[i].SetValue(HorizontalAlignmentProperty, HorizontalAlignment.Stretch);
itemsGrid.Children[i].SetValue(VerticalAlignmentProperty, VerticalAlignment.Stretch);
itemsGrid.Children[i].SetValue(Grid.RowProperty, i);
}
}
}
private void ItemsGrid_Loaded(object sender, RoutedEventArgs e)
{
itemsGrid = sender as GridWithChildChangedNoitfication;
if (itemsGrid != null)
{
itemsGrid.GridVisualChildrenChanged += GridChildrenChanged;
}
}
private void Expander_Expanded(object sender, RoutedEventArgs e)
{
Expander expander = sender as Expander;
var item = ItemsControl.ContainerFromElement(items, (DependencyObject)sender);
Int32 row = (Int32)(item).GetValue(Grid.RowProperty);
if (expander.Tag != null)
{
itemsGrid.RowDefinitions[row].Height = new GridLength((Double)expander.Tag, GridUnitType.Pixel);
}
}
private void Expander_Collapsed(object sender, RoutedEventArgs e)
{
Expander expander = sender as Expander;
var item = ItemsControl.ContainerFromElement(items, (DependencyObject)sender);
Int32 row = (Int32)(item).GetValue(Grid.RowProperty);
if (expander.Tag == null)
{
expander.Tag = itemsGrid.RowDefinitions[row].Height.Value;
}
itemsGrid.RowDefinitions[row].Height = new GridLength(40, GridUnitType.Pixel);
}
}