仔细想想，这个功能存在于ViewModel中，与Tab控件处于同一“级别”。

<Grid>
   <TabControl Items="{Binding MyTabViewModels}" SelectedItem={Binding SelectedTab} />
</Grid>

MyTabViewModel的示例上有一个集合：

public ObservableCollection<MyCollectionType> Items

项类MyCollectionType具有IsExpanded属性...

public bool IsExpanded {get;set;}

绑定到您的Expander控件IsExpanded属性。
把你的扣子塞进XAML

<Grid>
   <TabControl Items="{Binding MyTabViewModels}" />
   <Button Commmand={Binding ExpandAllCommand} />
</Grid>

现在，在ViewModel的基础上，ICommand可以执行以下操作：

public void ExpandAllCommandExecuted()
{
    foreach(var vm in SelectedTab.Items)
    {
        vm.IsExpanded = true;
    }
}

祝你好运，这都是伪代码，但说明了一个潜在的模式。

这个问题似乎是由于把我的<canvas>控件放在<scrollviewer>控件里面而引起的。我把它放在它外面，同时尝试了很多东西，它看起来像我想要的那样工作。按钮在标签栏（TabStrip）的顶部是可见的。
我的XAML现在是：

<TabControl Grid.Row="1" Grid.Column="0" VerticalAlignment="Stretch">
    <TabItem Header="Current">
        <StackPanel>
            <Canvas>
                <StackPanel Orientation="Horizontal" Canvas.Right="0" Canvas.Bottom="10" Spacing="5">
                    <Button Command="{Binding CollapseAll}" IsEnabled="{Binding !AllAreCollapsed}">Collapse All</Button>
                    <Button Command="{Binding ExpandAll}"   IsEnabled="{Binding !AllAreExpanded}">Expand All</Button>
                </StackPanel>
            </Canvas>

            <ScrollViewer Classes="CrawlersInAction">
                <StackPanel>
                    <ItemsControl Name="itemscontrol" Items="{Binding SiteInfos}" VerticalAlignment="Stretch">
                        <ItemsControl.ItemTemplate>
                            <DataTemplate>
                                <Expander ExpandDirection="Down" IsExpanded="{Binding IsExpanded, Mode=TwoWay}" VerticalAlignment="Stretch">
                                    <!-- Ommited my very long template code -->
                                </Expander>
                            <DataTemplate>
                        <ItemsControl.ItemTemplate>
                    <ItemsControl>
                </StackPanel>
            </ScrollViewer>
        </StackPanel>
    </TabItem>
</TabControl>

最后，我在代码方面向SiteInfo类添加了一个“IsExpanded”属性，该属性用作扩展器IsExpanded属性的基础，并通过按照上面的XAML使其成为双向绑定来保持同步。SiteInfo上的代码如下：

public class SiteInfo : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler? PropertyChanged;

        public static readonly bool StartIsExpanded = true;
        private bool _isExpanded = StartIsExpanded;
        public bool IsExpanded
        {
            get { return _isExpanded; }
            set
            {
                if (value != IsExpanded)
                {
                    _isExpanded = value;
                    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsExpanded)));
                }
            }
        }

当我在MainWindowViewModel中创建我的SiteInfo对象时，我订阅了事件（siteInfo.PropertyChanged += SiteInfo_PropertyChanged;）。当接收到事件时，如果我的折叠或展开所有按钮应被禁用，它将发生变化，它将发送自己的PropertyChangedEvent，然后启用/禁用控件。

public class MainWindowViewModel : ViewModelBase, INotifyPropertyChanged
    {

        public new event PropertyChangedEventHandler? PropertyChanged;
        public ObservableCollection<SiteInfo> SiteInfos { get; } 
            = new ObservableCollection<SiteInfo>();

        //Change SiteInfo.StartExpanded if you want this changed.
        private bool _allAreExpanded = SiteInfo.StartIsExpanded;
        public bool AllAreExpanded
        {
            get => _allAreExpanded;
            set
            {
                if (_allAreExpanded != value)
                {
                    _allAreExpanded = value;
                    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(AllAreExpanded)));
                }
            }
        }
        //Change SiteInfo.StartExpanded if you want this changed.
        private bool _allAreCollapsed = !SiteInfo.StartIsExpanded;
        public bool AllAreCollapsed {
            get { return _allAreCollapsed; }
            set {
                if (_allAreCollapsed != value)
                {
                    _allAreCollapsed = value;
                    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(AllAreCollapsed)));
                }
            }
        }

        private void SiteInfo_PropertyChanged(object? sender, PropertyChangedEventArgs e)
        {
            if(e.PropertyName == nameof(siteInfo.IsExpanded))
            {
                AllAreCollapsed = AreAllCollapsed();
                AllAreExpanded = AreAllExpanded();
            }
        }

        public bool AreAllCollapsed()
        {
            return !SiteInfos.Any<SiteInfo>( siteInfo => siteInfo.IsExpanded );
        }

        public bool AreAllExpanded()
        {
            return !SiteInfos.Any<SiteInfo>( siteInfo => siteInfo.IsCollapsed);
        }

        public void CollapseAll()
        {
            foreach(SiteInfo siteInfo in SiteInfos)
            {
                siteInfo.IsExpanded = false;
            }
        }
        public void ExpandAll()
        {
            foreach (SiteInfo siteInfo in SiteInfos)
            {
                siteInfo.IsExpanded = true;
            }
        }
    }

我想我会添加我的代码的其余部分，以防有人谷歌这一点，并希望做类似的事情。
现在，当我的程序加载并且所有内容都设置为默认展开true时，“全部展开”被禁用，“全部折叠”被启用。将一个展开器更改为折叠状态将启用两个按钮，而折叠所有展开器将禁用"全部折叠“按钮。x1c 0d1x