如何通过EventHandler从Rg.Plugins.Popup获取动态值（不使用MessagingCenter）

我在学习Xamarin Forms，需要在Popup关闭时动态获取其内部CollectionView的选中项。因为代码要在关闭后立即使用选中值，MessagingCenter表现不佳，所以选择用EventHandler实现。但当前遇到问题：调用Popup的PrimaryCommand时，新建的MyGamePopup实例无法获取已打开Popup里更新的ListLangFilter变量值，不知道如何正确获取选中项。

Popup XAML代码 #

<Grid RowDefinitions="*,50" >

<CollectionView Grid.Row="0" x:Name="QuestionLangListView" SelectionMode="Single" SelectionChanged="OnselectLanguageList" >

<CollectionView.ItemTemplate>
<DataTemplate>
<Label Grid.Column="0" TextColor="{StaticResource MySecondColor }"   HorizontalTextAlignment="Start" Text="{Binding LanguageKey2}" Style="{StaticResource NormalSizeLabel }"/>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
       
<StackLayout Grid.Row="1" >
 <!--关闭Popup的区域-->
<StackLayout.GestureRecognizers>
    <TapGestureRecognizer  Command="{Binding PrimaryCommand , Source={Reference ThisPopUpPage}}"/>
</StackLayout.GestureRecognizers>

</StackLayout>

</Grid>

Popup C#代码 #

string ListLangFilter;
void OnselectLanguageList(System.Object sender, Xamarin.Forms.SelectionChangedEventArgs e)
{
var word = (string)e.CurrentSelection.FirstOrDefault();

// 更新全局变量存储选中值
ListLangFilter = word;
}

public event EventHandler<object> ClickEvent;
public void OnStartGame()
{
     ClickEvent?.Invoke(this, ListLangFilter);
}

调用Popup的代码 #

await PopupNavigation.Instance.PushAsync(new Mypopup.MyGamePopup(LangQuestionList)
{
PrimaryCommand = new Command(async () =>
{
    await PopupNavigation.Instance.PopAsync(true);

    Mypopup.MyGamePopup gamepopop = new Mypopup.MyGamePopup(LangQuestionList);

    gamepopop.ClickEvent += (s,args) =>
    {
        Console.WriteLine("your arg value is  "+ args);
    };

    gamepopop.OnStartGame();
})
});

核心问题 #

新建的MyGamePopup实例是完全独立的对象，并非当前正在关闭的Popup，因此无法获取用户实际选中的ListLangFilter值。

问题的核心是你没有引用当前打开的Popup实例，而是新建了一个无关的对象。下面是两种可行的修复方式：

方式1：提前创建Popup实例并绑定事件 #

提前实例化Popup对象，直接在PrimaryCommand中使用该实例触发事件或获取选中值：

// 提前创建Popup实例
var gamePopup = new Mypopup.MyGamePopup(LangQuestionList);

// 绑定事件监听选中值
gamePopup.ClickEvent += (s, args) =>
{
    Console.WriteLine("your arg value is  " + args);
    // 在这里直接执行选中值的后续逻辑
};

// 设置PrimaryCommand，直接使用已创建的实例
gamePopup.PrimaryCommand = new Command(async () =>
{
    // 先触发事件传递选中值
    gamePopup.OnStartGame();
    // 再关闭Popup
    await PopupNavigation.Instance.PopAsync(true);
});

// 弹出Popup
await PopupNavigation.Instance.PushAsync(gamePopup);

方式2：在Popup中公开选中值属性（更优雅） #

在MyGamePopup类中添加公开属性存储选中值，避免依赖全局变量，直接通过实例获取：

// 在MyGamePopup类中新增公开属性
public string SelectedLanguage { get; private set; }

// 修改选中事件方法
void OnselectLanguageList(System.Object sender, Xamarin.Forms.SelectionChangedEventArgs e)
{
    SelectedLanguage = (string)e.CurrentSelection.FirstOrDefault();
}

// 可选：修改事件触发方法
public void OnStartGame()
{
     ClickEvent?.Invoke(this, SelectedLanguage);
}

此时在调用代码中，无需事件也能直接获取选中值：

var gamePopup = new Mypopup.MyGamePopup(LangQuestionList);

gamePopup.PrimaryCommand = new Command(async () =>
{
    // 直接获取选中值
    var selectedValue = gamePopup.SelectedLanguage;
    Console.WriteLine("your arg value is  " + selectedValue);
    await PopupNavigation.Instance.PopAsync(true);
});

await PopupNavigation.Instance.PushAsync(gamePopup);

内容的提问来源于stack exchange，提问作者hugo