MAUI Community Toolkit关闭Popup时触发空引用异常求助

问题重现 #

在MAUI应用中使用CommunityToolkit.Maui的Popup实现加载提示，在页面OnAppearing方法中显示弹窗、执行异步初始化后关闭，触发空引用异常：

Object reference not set to an instance of an object.
at CommunityToolkit.Maui.Views.Popup.CommunityToolkit.Maui.Core.IPopup.OnClosed(Object result)
at CommunityToolkit.Maui.Views.Popup.d__62.MoveNext()
at CommunityToolkit.Maui.Views.Popup.d__60.MoveNext()
at LanguageInUse.Views.DictionaryList.d__3.MoveNext() in C:\Projects\ERDevOps\LIUApp\LanguageInUse\Views\DictionaryList.xaml.cs:line 32

弹窗已正常实例化，但关闭时仍报错。

解决方案 #

1. 改用Loaded事件替代OnAppearing #

OnAppearing触发时机早于页面完全渲染完成，此时弹窗可能尚未完成内部初始化。改用页面的Loaded事件，确保UI元素都已就绪：

public DictionaryList()
{
    InitializeComponent();
    Loaded += OnPageLoaded;
}

private async void OnPageLoaded(object sender, EventArgs e)
{
    var popup = new LoadingPopup();
    this.ShowPopup(popup);

    await vm.Init();

    // 先判断弹窗是否处于打开状态再关闭
    if (popup.IsOpen)
    {
        await popup.CloseAsync();
    }
}

2. 升级CommunityToolkit.Maui到最新稳定版 #

旧版本的CommunityToolkit.Maui存在Popup关闭时的空引用bug，已在后续版本修复。打开NuGet包管理器，将CommunityToolkit.Maui更新至当前最新稳定版（如8.0.0及以上）。

3. 通过Dispatcher调度关闭操作 #

确保关闭弹窗的操作在正确的UI线程上下文执行，避免因线程调度问题导致内部引用为空：

protected override async void OnAppearing()
{
    base.OnAppearing();

    var popup = new LoadingPopup();
    this.ShowPopup(popup);

    await vm.Init();

    // 用Dispatcher确保UI线程执行关闭操作
    await Dispatcher.DispatchAsync(async () =>
    {
        if (popup != null && popup.IsOpen)
        {
            await popup.CloseAsync();
        }
    });
}

4. 封装异步初始化逻辑（避免async void风险） #

async void的生命周期方法异常难以捕获，可将初始化逻辑封装为独立异步方法：

protected override async void OnAppearing()
{
    base.OnAppearing();
    await InitializeDataAsync();
}

private async Task InitializeDataAsync()
{
    var popup = new LoadingPopup();
    this.ShowPopup(popup);

    try
    {
        await vm.Init();
    }
    finally
    {
        if (popup.IsOpen)
        {
            await popup.CloseAsync();
        }
    }
}

内容的提问来源于stack exchange，提问作者Enrico