winui3问题：点击事件不生效

<pre class="EnlighterJSRAW" data-enlighter-group="" data-enlighter-highlight="" data-enlighter-language="csharp" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-theme="" data-enlighter-title=""><Window
    x:Class="App1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App1"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
    <SplitView IsPaneOpen="True" x:Name="splitView" PaneBackground="{ThemeResource SystemControlBackgroundChromeMediumLowBrush}"
               OpenPaneLength="256" CompactPaneLength="48" DisplayMode="CompactInline">
        <SplitView.Pane>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="56" />
                    <ColumnDefinition Width="*" />
                </Grid.ColumnDefinitions>

                <StackPanel Orientation="Vertical" Grid.Column="0" Margin="0,20,0,0">
                    <AppBarButton Icon="GlobalNavigationButton" Click="OnOpenPane" Margin="-10,0,0,0"/>
                    <AppBarButton Icon="Add" Label="Add" Click="OnOpenPane" Margin="-10,0,0,0"/>
                    <AppBarButton Icon="Edit" Label="Add" Click="OnOpenPane" Margin="-10,0,0,0"/>
                    <AppBarButton Icon="Setting" Label="Add" Click="OnOpenPane" Margin="-10,0,0,0"/>
                </StackPanel>

                <TreeView x:Name="treeView1" 
                    Grid.Column="1"
                    SelectionMode="Single">
                </TreeView>
            </Grid>
        </SplitView.Pane>
        Grid>
            <TabView x:Name="Tabs" />
        </Grid>
    </SplitView>
</Window>

大概这样的XAML，整体是一个SplitView，左侧的Pane分两部分，左侧是一列按钮，右侧是一个TreeView，SplitView的右侧是一个TabView。不得不说，winui的新UI确实漂亮，而且XAML设计界面也很快捷，就是winui好像还不支持可视化设计，只能手写XAML，权当学习了吧。