Question

我知道如何在代码中执行此操作，但这可以在XAML中完成吗？

Window1.xaml：

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <Grid>
        <ComboBox Name="ComboBox1" HorizontalAlignment="Left" VerticalAlignment="Top">
            <ComboBoxItem>ComboBoxItem1</ComboBoxItem>
            <ComboBoxItem>ComboBoxItem2</ComboBoxItem>
        </ComboBox>
    </Grid>
</Window>

Window1.xaml.cs：

using System.Windows;
using System.Windows.Controls;

namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            double width = 0;
            foreach (ComboBoxItem item in ComboBox1.Items)
            {
                item.Measure(new Size(
                    double.PositiveInfinity, double.PositiveInfinity));
                if (item.DesiredSize.Width > width)
                    width = item.DesiredSize.Width;
            }
            ComboBox1.Measure(new Size(
                double.PositiveInfinity, double.PositiveInfinity));
            ComboBox1.Width = ComboBox1.DesiredSize.Width + width;
        }
    }
}

Answer 1

您不能直接在Xaml中执行此操作，但可以使用此附加行为。（宽度将在Designer中可见）

<ComboBox behaviors:ComboBoxWidthFromItemsBehavior.ComboBoxWidthFromItems="True">
    <ComboBoxItem Content="Short"/>
    <ComboBoxItem Content="Medium Long"/>
    <ComboBoxItem Content="Min"/>
</ComboBox>

附加行为ComboBoxWidthFromItemsProperty

public static class ComboBoxWidthFromItemsBehavior
{
    public static readonly DependencyProperty ComboBoxWidthFromItemsProperty =
        DependencyProperty.RegisterAttached
        (
            "ComboBoxWidthFromItems",
            typeof(bool),
            typeof(ComboBoxWidthFromItemsBehavior),
            new UIPropertyMetadata(false, OnComboBoxWidthFromItemsPropertyChanged)
        );
    public static bool GetComboBoxWidthFromItems(DependencyObject obj)
    {
        return (bool)obj.GetValue(ComboBoxWidthFromItemsProperty);
    }
    public static void SetComboBoxWidthFromItems(DependencyObject obj, bool value)
    {
        obj.SetValue(ComboBoxWidthFromItemsProperty, value);
    }
    private static void OnComboBoxWidthFromItemsPropertyChanged(DependencyObject dpo,
                                                                DependencyPropertyChangedEventArgs e)
    {
        ComboBox comboBox = dpo as ComboBox;
        if (comboBox != null)
        {
            if ((bool)e.NewValue == true)
            {
                comboBox.Loaded += OnComboBoxLoaded;
            }
            else
            {
                comboBox.Loaded -= OnComboBoxLoaded;
            }
        }
    }
    private static void OnComboBoxLoaded(object sender, RoutedEventArgs e)
    {
        ComboBox comboBox = sender as ComboBox;
        Action action = () => { comboBox.SetWidthFromItems(); };
        comboBox.Dispatcher.BeginInvoke(action, DispatcherPriority.ContextIdle);
    }
}

它的作用是调用ComboBox的一个名为SetWidthFromItems的扩展方法，它（无形地）展开并折叠自身，然后根据生成的ComboBoxItems计算宽度。（IExpandCollapseProvider需要引用UIAutomationProvider.dll）

然后扩展方法SetWidthFromItems

public static class ComboBoxExtensionMethods
{
    public static void SetWidthFromItems(this ComboBox comboBox)
    {
        double comboBoxWidth = 19;// comboBox.DesiredSize.Width;

        // Create the peer and provider to expand the comboBox in code behind. 
        ComboBoxAutomationPeer peer = new ComboBoxAutomationPeer(comboBox);
        IExpandCollapseProvider provider = (IExpandCollapseProvider)peer.GetPattern(PatternInterface.ExpandCollapse);
        EventHandler eventHandler = null;
        eventHandler = new EventHandler(delegate
        {
            if (comboBox.IsDropDownOpen &&
                comboBox.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
            {
                double width = 0;
                foreach (var item in comboBox.Items)
                {
                    ComboBoxItem comboBoxItem = comboBox.ItemContainerGenerator.ContainerFromItem(item) as ComboBoxItem;
                    comboBoxItem.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
                    if (comboBoxItem.DesiredSize.Width > width)
                    {
                        width = comboBoxItem.DesiredSize.Width;
                    }
                }
                comboBox.Width = comboBoxWidth + width;
                // Remove the event handler. 
                comboBox.ItemContainerGenerator.StatusChanged -= eventHandler;
                comboBox.DropDownOpened -= eventHandler;
                provider.Collapse();
            }
        });
        comboBox.ItemContainerGenerator.StatusChanged += eventHandler;
        comboBox.DropDownOpened += eventHandler;
        // Expand the comboBox to generate all its ComboBoxItem's. 
        provider.Expand();
    }
}

此扩展方法还提供了调用

的功能

comboBox.SetWidthFromItems();

在后面的代码中（例如在ComboBox.Loaded事件中）

Answer 2

如果没有：

，则不能在XAML中

创建隐藏控件（Alan Hunford的回答）
彻底改变ControlTemplate。即使在这种情况下，也可能需要创建ItemsPresenter的隐藏版本。

原因是我遇到的默认ComboBox ControlTemplates（Aero，Luna等）都将ItemsPresenter嵌套在Popup中。这意味着这些项目的布局会延迟，直到它们实际可见。

一种简单的方法是修改默认的ControlTemplate，将最外层容器的MinWidth（它是Aero和Luna的Grid）绑定到PART_Popup的ActualWidth。单击下拉按钮时，您可以让ComboBox自动同步它的宽度，而不是之前。

因此，除非您可以在布局系统中强制执行测量操作（通过添加第二个控件可以执行此操作），我认为无法完成。

与往常一样，我对一个简短而优雅的解决方案持开放态度 - 但在这种情况下，代码隐藏或双控制/ ControlTemplate黑客是我见过的唯一解决方案。

Answer 3

是的，这个有点讨厌。

我过去所做的是在ControlTemplate中添加一个隐藏的列表框（其itemscontainerpanel设置为网格）同时显示每个项目，但其可见性设置为隐藏。

我很高兴听到任何更好的想法不依赖于可怕的代码隐藏或您的观点必须理解它需要使用不同的控件来提供宽度来支持视觉效果（哎呀！）

Answer 4

根据上面的其他答案，这是我的版本：

<Grid HorizontalAlignment="Left">
    <ItemsControl ItemsSource="{Binding EnumValues}" Height="0" Margin="15,0"/>
    <ComboBox ItemsSource="{Binding EnumValues}" />
</Grid>

HorizontalAlignment =“Left”使用包含控件的整个宽度来停止控件。高度=“0”隐藏物品控制 Margin =“15,0”允许在组合框项目周围添加额外的铬（我不害怕Chrome不可知）。

Answer 5

我最终得到了一个“足够好”的解决方案，这个问题是让组合框永远不会缩小到它所持有的最大尺寸，类似于旧的WinForms AutoSizeMode = GrowOnly。

我这样做的方法是使用自定义值转换器：

public class GrowConverter : IValueConverter
{
    public double Minimum
    {
        get;
        set;
    }

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var dvalue = (double)value;
        if (dvalue > Minimum)
            Minimum = dvalue;
        else if (dvalue < Minimum)
            dvalue = Minimum;
        return dvalue;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

然后我在XAML中配置组合框，如下所示：

 <Whatever>
        <Whatever.Resources>
            <my:GrowConverter x:Key="grow" />
        </Whatever.Resources>
        ...
        <ComboBox MinWidth="{Binding ActualWidth,RelativeSource={RelativeSource Self},Converter={StaticResource grow}}" />
    </Whatever>

请注意，对于每个组合框，您需要一个单独的GrowConverter实例，除非您希望它们的一组大小一起，类似于Grid的SharedSizeScope功能。

Answer 6

跟随Maleak的回答：我非常喜欢这个实现，我为它写了一个实际的行为。显然你需要Blend SDK才能引用System.Windows.Interactivity。

XAML：

    <ComboBox ItemsSource="{Binding ListOfStuff}">
        <i:Interaction.Behaviors>
            <local:ComboBoxWidthBehavior />
        </i:Interaction.Behaviors>
    </ComboBox>

代码：

using System;
using System.Windows;
using System.Windows.Automation.Peers;
using System.Windows.Automation.Provider;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Interactivity;

namespace MyLibrary
{
    public class ComboBoxWidthBehavior : Behavior<ComboBox>
    {
        protected override void OnAttached()
        {
            base.OnAttached();
            AssociatedObject.Loaded += OnLoaded;
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
            AssociatedObject.Loaded -= OnLoaded;
        }

        private void OnLoaded(object sender, RoutedEventArgs e)
        {
            var desiredWidth = AssociatedObject.DesiredSize.Width;

            // Create the peer and provider to expand the comboBox in code behind. 
            var peer = new ComboBoxAutomationPeer(AssociatedObject);
            var provider = peer.GetPattern(PatternInterface.ExpandCollapse) as IExpandCollapseProvider;
            if (provider == null)
                return;

            EventHandler[] handler = {null};    // array usage prevents access to modified closure
            handler[0] = new EventHandler(delegate
            {
                if (!AssociatedObject.IsDropDownOpen || AssociatedObject.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)
                    return;

                double largestWidth = 0;
                foreach (var item in AssociatedObject.Items)
                {
                    var comboBoxItem = AssociatedObject.ItemContainerGenerator.ContainerFromItem(item) as ComboBoxItem;
                    if (comboBoxItem == null)
                        continue;

                    comboBoxItem.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
                    if (comboBoxItem.DesiredSize.Width > largestWidth)
                        largestWidth = comboBoxItem.DesiredSize.Width;
                }

                AssociatedObject.Width = desiredWidth + largestWidth;

                // Remove the event handler.
                AssociatedObject.ItemContainerGenerator.StatusChanged -= handler[0];
                AssociatedObject.DropDownOpened -= handler[0];
                provider.Collapse();
            });

            AssociatedObject.ItemContainerGenerator.StatusChanged += handler[0];
            AssociatedObject.DropDownOpened += handler[0];

            // Expand the comboBox to generate all its ComboBoxItem's. 
            provider.Expand();
        }
    }
}

Answer 7

将包含相同内容的列表框放在保管箱后面。然后用这样的绑定强制执行正确的高度：

<Grid>
       <ListBox x:Name="listBox" Height="{Binding ElementName=dropBox, Path=DesiredSize.Height}" /> 
        <ComboBox x:Name="dropBox" />
</Grid>

Answer 8

在我的情况下，一个更简单的方法似乎可以做到这一点，我只是使用了额外的stackPanel来包装组合框。

<StackPanel Grid.Row="1" Orientation="Horizontal">
    <ComboBox ItemsSource="{Binding ExecutionTimesModeList}" Width="Auto"
        SelectedValuePath="Item" DisplayMemberPath="FriendlyName"
        SelectedValue="{Binding Model.SelectedExecutionTimesMode}" />    
</StackPanel>

（在visual studio 2008工作）

Answer 9

当我遇到每个UpdateLayout()所拥有的UIElement方法时，我一直在寻找答案。

现在很简单，谢天谢地！

设置或修改ComboBox1.Updatelayout();后，只需致电ItemSource。

Answer 10

Alun Harford的方法，在实践中：

<Grid>

  <Grid.ColumnDefinitions>
    <ColumnDefinition Width="Auto"/>
    <ColumnDefinition Width="*"/>
  </Grid.ColumnDefinitions>

  <!-- hidden listbox that has all the items in one grid -->
  <ListBox ItemsSource="{Binding Items, ElementName=uiComboBox, Mode=OneWay}" Height="10" VerticalAlignment="Top" Visibility="Hidden">
    <ListBox.ItemsPanel><ItemsPanelTemplate><Grid/></ItemsPanelTemplate></ListBox.ItemsPanel>
  </ListBox>

  <ComboBox VerticalAlignment="Top" SelectedIndex="0" x:Name="uiComboBox">
    <ComboBoxItem>foo</ComboBoxItem>
    <ComboBoxItem>bar</ComboBoxItem>
    <ComboBoxItem>fiuafiouhoiruhslkfhalsjfhalhflasdkf</ComboBoxItem>
  </ComboBox>

</Grid>

Answer 11

这样可以将宽度保持为最宽的元素，但只能在打开组合框后一次。

<ComboBox ItemsSource="{Binding ComboBoxItems}" Grid.IsSharedSizeScope="True" HorizontalAlignment="Left">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition SharedSizeGroup="sharedSizeGroup"/>
                </Grid.ColumnDefinitions>
                <TextBlock Text="{Binding}"/>
            </Grid>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

Answer 12

top answer的另一种解决方案是Measure the Popup本身而不是测量所有项目。提供稍微简单的SetWidthFromItems()实现：

private static void SetWidthFromItems(this ComboBox comboBox)
{
    if (comboBox.Template.FindName("PART_Popup", comboBox) is Popup popup 
        && popup.Child is FrameworkElement popupContent)
    {
        popupContent.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
        // suggested in comments, original answer has a static value 19.0
        var emptySize = SystemParameters.VerticalScrollBarWidth + comboBox.Padding.Left + comboBox.Padding.Right;
        comboBox.Width = emptySize + popupContent.DesiredSize.Width;
    }
}

也可以在禁用的ComboBox上运行。

Answer 13

我希望仅在下拉列表打开时将其大小调整为最大元素，否则将其调整为所选值。这是该代码：

部分基于弗雷德里克（Frederik）的回答（这实际上对我不起作用）

public static class ComboBoxAutoWidthBehavior {
    public static readonly DependencyProperty ComboBoxAutoWidthProperty =
            DependencyProperty.RegisterAttached(
                "ComboBoxAutoWidth",
                typeof(bool),
                typeof(ComboBoxAutoWidthBehavior),
                new UIPropertyMetadata(false, OnComboBoxAutoWidthPropertyChanged)
            );

    public static bool GetComboBoxAutoWidth(DependencyObject obj) {
        return (bool) obj.GetValue(ComboBoxAutoWidthProperty);
    }

    public static void SetComboBoxAutoWidth(DependencyObject obj, bool value) {
        obj.SetValue(ComboBoxAutoWidthProperty, value);
    }

    private static void OnComboBoxAutoWidthPropertyChanged(DependencyObject dpo, DependencyPropertyChangedEventArgs e) {
        if(dpo is ComboBox comboBox) {
            if((bool) e.NewValue) {
                comboBox.Loaded += OnComboBoxLoaded;
                comboBox.DropDownOpened += OnComboBoxOpened;
                comboBox.DropDownClosed += OnComboBoxClosed;
            } else {
                comboBox.Loaded -= OnComboBoxLoaded;
                comboBox.DropDownOpened -= OnComboBoxOpened;
                comboBox.DropDownClosed -= OnComboBoxClosed;
            }
        }
    }

    private static void OnComboBoxLoaded(object sender, EventArgs eventArgs) {
        ComboBox comboBox = (ComboBox) sender;
        comboBox.SetMaxWidthFromItems();
    }

    private static void OnComboBoxOpened(object sender, EventArgs eventArgs) {
        ComboBox comboBox = (ComboBox) sender;
        comboBox.Width = comboBox.MaxWidth;
    }

    private static void OnComboBoxClosed(object sender, EventArgs eventArgs) => ((ComboBox) sender).Width = double.NaN;
}

public static class ComboBoxExtensionMethods {
    public static void SetMaxWidthFromItems(this ComboBox combo) {
        double idealWidth = combo.MinWidth;
        string longestItem = combo.Items.Cast<object>().Select(x => x.ToString()).Max(x => (x?.Length, x)).x;
        if(longestItem != null && longestItem.Length >= 0) {
            string tmpTxt = combo.Text;
            combo.Text = longestItem;
            Thickness tmpMarg = combo.Margin;
            combo.Margin = new Thickness(0);
            combo.UpdateLayout();

            combo.Width = double.NaN;
            combo.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));

            idealWidth = Math.Max(idealWidth, combo.DesiredSize.Width);

            combo.Text = tmpTxt;
            combo.Margin = tmpMarg;
        }

        combo.MaxWidth = idealWidth;
    }
}

您可以这样启用它：

<ComboBox behaviours:ComboBoxAutoWidthBehavior.ComboBoxAutoWidth="True" />

您也可以直接设置Width而不是MaxWidth，然后删除DropDownOpened和Closed部分，如果您希望它的行为与其他anwsers类似。

Answer 14

只需在组合框中添加宽度

<ComboBox Name="ComboBox1" HorizontalAlignment="Left" VerticalAlignment="Top" Width="100">

如何使WPF组合框具有XAML中最宽元素的宽度？

14 个答案: