在内容页面XAMARIN FORMS中调用onresumo（）方法

Question

我在iOS中的声明中遇到以下问题。当用户在后台返回到应用程序时，我需要激活一个命令。在我身上，ContentPage我找不到识别退货的方法。在Android中，它可以正常工作，仅在iOS中，我无法在内容中找到任何表明我要返回的函数

 protected override void OnAppearing()
    {
        Debug.WriteLine("OnAppearing()");
        base.OnAppearing();
    }

    protected override void OnDisappearing()
    {
        Debug.WriteLine("OnDisappearing");
        base.OnDisappearing();
    }

    protected override void OnBindingContextChanged()
    {
        Debug.WriteLine("OnBindingContextChanged");
        base.OnBindingContextChanged();
    }

我尝试了三种选择，但没有结果

Answer 1

正如 josemigallas 所说，您正在寻找App.OnResume(). 您可以轻松订阅和取消订阅一个MessagingCenter事件，该事件可以从您的App.OnResume()方法发送以触​​发您ContentPage订阅的每个s 中的操作（不要忘记取消订阅其中的事件ContentPage.OnDisappearing()以防止内存泄漏）：

在你ContentPage的：

protected override void OnAppearing() {
    Debug.WriteLine("OnAppearing()");
    base.OnAppearing();

    MessagingCenter.Subscribe<App>(this, "SpecialOnResumeKeyValue", app => {
            //Do something
    };
}

protected override void OnDisappearing() {
    Debug.WriteLine("OnDisappearing");
    base.OnDisappearing();

    MessagingCenter.Unsubscribe<App>(this, "SpecialOnResumeKeyValue"); //VERY IMPORTANT
}

然后在您的App.xaml.cs：

protected override async void OnResume() {
    MessagingCenter.Send(this, "SpecialOnResumeKeyValue");
}

Answer 2

我通常以这种方式这样做，所以我不必打扰订阅：

public partial class App : Application
{
    public App()
    {
        InitializeComponent();

        MainPage = new MainPage();
    }

    protected override async void OnStart()
    {
        if (Application.Current.MainPage is IAppStateAware appStateAwarePage)
            await appStateAwarePage.OnStartApplicationAsync();
        if (Application.Current.MainPage.BindingContext is IAppStateAware appStateAwareVm)
            await appStateAwareVm.OnStartApplicationAsync();
        // Handle when your app starts
    }

    protected override async void OnSleep()
    {
        if (Application.Current.MainPage is IAppStateAware appStateAwarePage)
            await appStateAwarePage.OnSleepApplicationAsync();
        if (Application.Current.MainPage.BindingContext is IAppStateAware appStateAwareVm)
            await appStateAwareVm.OnSleepApplicationAsync();
        // Handle when your app sleeps
    }

    protected override async void OnResume()
    {
        if (Application.Current.MainPage is IAppStateAware appStateAwarePage)
            await appStateAwarePage.OnResumeApplicationAsync();
        if (Application.Current.MainPage.BindingContext is IAppStateAware appStateAwareVm)
            await appStateAwareVm.OnResumeApplicationAsync();
        // Handle when your app resumes
    }
}

public class YourContentPage : Page, IAppStateAware
{
    public Task OnResumeApplicationAsync()
    {
        throw new System.NotImplementedException();
    }

    public Task OnSleepApplicationAsync()
    {
        throw new System.NotImplementedException();
    }

    public Task OnStartApplicationAsync()
    {
        throw new System.NotImplementedException();
    }
}

public interface IAppStateAware
{
    Task OnResumeApplicationAsync();
    Task OnSleepApplicationAsync();
    Task OnStartApplicationAsync();
}