Xamarin 形成 PopupPage

Question

我正在使用 Rg.Plugins.Popup.Pages 作为弹出页面，当我按下一个按钮时，弹出窗口出现在页面中间，我在其中有一个 select 的单选按钮，当我完成时，我触摸透明背景退出。我的问题是，在后台页面中，我有一个标签，我需要根据我在页面的 onAppearing 方法的弹出页面中选择的内容进行修改，每当我触摸弹出页面的背景消失和背景的 onAppearing页面永远不会被调用！

按钮放在后台页面

 protected override void OnAppearing()
        {
            for (int i = 0; i < TestingClass.multiselection.Count; i++)
            {
                if (TestingClass.multiselection[i].is_selected)
                    btn.Text += TestingClass.multiselection[i].description;
            }
            base.OnAppearing();
        }

当弹出窗口出现时，我从静态 class 中获取值，值是这样保存的：

private void RadioButton_Clicked(object sender, System.EventArgs e)
        {
            var rb = sender as RadioButton;
            var selection = rb.BindingContext as multi_selection;
            if (selection != null && selection.is_selected == true)
            {
                selection.is_selected = false;
            }
            else
            if (selection != null && selection.is_selected == false)
            {
                selection.is_selected = true;
                TestingClass.multiselection.Add(selection);
            }
        }

Answer 1

根据平台的不同，OnApperearing 可能只被调用一次。也许您可以将其翻转并连接到弹出页面的 OnDisappearing 并使用它来更新您的值？

Answer 2

有两种方法（据我所知）：

您可以在 PopupPage 中创建 EventHandler 并在初始化此 popupPage 时订阅它：
```
MyPopupPage popup = new MyPopupPage();
// Subscribe event
popup.Save += SaveEventHandlerArgs;
Navigation.PushPopupAsync(popup);
```
在您的 popupPage 中选择一个值后，调用您的事件处理程序并将值作为参数传递。之后 SaveEventHandlerArgs 方法将被调用，在那里你可以得到你的价值并用它做你想做的事；

Examples of using events
可以使用MessagingCenter。示例在 link.

希望对您有所帮助！

Answer 3

当您在视图中添加弹出窗口时，不会调用 OnApperearing 和 OnDisappearing。

在Apple document中说：

viewWillAppear:

This method is called before the view controller's view is about to be added to a view hierarchy and before any animations are configured for showing the view.

在Android中：

OnCreate

OnCreate is the first method to be called when an activity is created.

添加弹出窗口或删除弹出窗口既不是 create/remove 新视图也不是 add/remove 视图 to/from 层次结构。所以，这些生命周期方法不会在那个时候被调用。

解法：

关于弹窗选择后如何设置按钮的文字，我同意Денис Чорный的回答，我用代码说明一下。

1.Use eventHandle:

在弹出页面中，定义一个EventHandler:

public EventHandler SelectedStringChanged { get; set; }

在您的 RadioButton_Clicked 中，添加一行以调用 SelectedStringChanged:

    private void RadioButton_Clicked(object sender, System.EventArgs e)
    {
        var rb = sender as RadioButton;
        var selection = rb.BindingContext as multi_selection;
        if (selection != null && selection.is_selected == true)
        {
            selection.is_selected = false;
        }
        else
        if (selection != null && selection.is_selected == false)
        {
            selection.is_selected = true;
            TestingClass.multiselection.Add(selection);
        }

        //Add this line
        SelectedStringChanged(sender, e);
    }

在后台页面，创建一个方法来处理btn.text:

    private void Handle_SelectedStringChanged(object sender, EventArgs rags)
    {
        // ... your code
        for (int i = 0; i < TestingClass.multiselection.Count; i++)
        {
            if (TestingClass.multiselection[i].is_selected)
                btn.Text += TestingClass.multiselection[i].description;
        }
    }

弹出方法中，消费Handle_SelectedStringChanged方法：

    private async void OnOpenPupup(object sender, EventArgs e)
    {
        _loginPopup.SelectedStringChanged += Handle_SelectedStringChanged;

        await PopupNavigation.Instance.PushAsync(_loginPopup);
    }

MessageingCenter 也可以。

后台页面中：

   MessagingCenter.Subscribe<MainPage>(this, "stringSelected", (sender) => {
          // do something whenever the "stringSelected" message is sent
            for (int i = 0; i<TestingClass.multiselection.Count; i++)
                {
                    if (TestingClass.multiselection[i].is_selected)
                    btn.Text += TestingClass.multiselection[i].description;
                }
        });

在你弹出的页面中：

  private void RadioButton_Clicked(object sender, System.EventArgs e)
    {
        var rb = sender as RadioButton;
        var selection = rb.BindingContext as multi_selection;
        if (selection != null && selection.is_selected == true)
        {
            selection.is_selected = false;
        }
        else
        if (selection != null && selection.is_selected == false)
        {
            selection.is_selected = true;
            TestingClass.multiselection.Add(selection);
        }

        MessagingCenter.Send<MainPage>(this, "stringSelected");

    }

参考：messaging-center

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