Question

尝试使用Xamarin.Forms页面找到实现导航的最佳方式。

这是我的UI导航图

我正在使用mvvm。每个ViewModel都填充了INavigationService。

public class NavigationService : INavigationService
{
    private readonly NavigationPage navigationPage;

    private const string PageNameTemplate = "Mmv.MMTravel.CrossPlatform.Views.{0}, Mmv.MMTravel.CrossPlatform";

    public NavigationService(NavigationPage page)
    {
        navigationPage = page;
    }

    public string CurrentPageKey
    {
        get
        {
            return navigationPage.CurrentPage.GetType().Name;
        }
    }

    public async Task GoBackAsync()
    {
        await navigationPage.Navigation.PopAsync();
    }

    public async Task NavigateAsync(string pageKey, object parameter)
    {
        await CallOnNavigateFrom();
        var page = CreatePage(pageKey);
        await CallOnNavigateTo(page, parameter);
        if (Device.OS == TargetPlatform.Android)
        {
             Device.BeginInvokeOnMainThread(() =>
            {
                navigationPage.Navigation.PushAsync(page);
            });
        }
        else
        {
            await navigationPage.Navigation.PushAsync(page);
        }
    }

    public async Task NavigateAsync(string pageKey)
    {
        await NavigateAsync(pageKey, null);
    }

    public async Task SetAndNavigateToRootPage(string pageKey, object parameter)
    {
        await CallOnNavigateFrom();
        var page = CreatePage(pageKey);
        await CallOnNavigateTo(page, parameter);
        navigationPage.Navigation.InsertPageBefore(page, navigationPage.Navigation.NavigationStack.First());
        await navigationPage.PopToRootAsync(false);
    }

    public async Task SetAndNavigateToRootPage(string pageKey)
    {
        await SetAndNavigateToRootPage(pageKey, null);
    }

    public async Task NavigateModalAsync(string pageKey, object parameter)
    {
        await CallOnNavigateFrom();
        var page = CreatePage(pageKey);
        await CallOnNavigateTo(page, parameter);
        await navigationPage.Navigation.PushModalAsync(page);
    }

    public async Task NavigateModalAsync(string pageKey)
    {
        await NavigateModalAsync(pageKey, null);
    }

    public async Task GoBackModalAsync()
    {
        await navigationPage.Navigation.PopModalAsync();
    }

    private Page CreatePage(string pageKey)
    {
        var typeName = string.Format(PageNameTemplate, pageKey);
        var pageType = Type.GetType(typeName);
        var page = Activator.CreateInstance(pageType) as Page;
        return page;
    }

    private async Task CallOnNavigateTo(Page page, object parameter)
    {
        var vm = page.BindingContext as INavigateAwareViewModel;
        if (vm != null && !vm.IsBusy) 
        {
            await vm.OnNavigatedTo(parameter).ConfigureAwait(false);
        }
    }

    private async Task CallOnNavigateFrom()
    {
        if (navigationPage.CurrentPage != null)
        {
            var prevVM = navigationPage.CurrentPage.BindingContext as INavigateAwareViewModel;
            if (prevVM != null && !prevVM.IsBusy)
            {
                await prevVM.OnNavigatedFrom().ConfigureAwait(false);
            }
        }
    }
}

如您所见，我的NavigationService包含NavigationPage。因此，所有导航都通过NavigationPage中的Navigation属性进行。此外，每个viewmodel都具有异步init的OnNvaigateTo（）和OnNavigateFrom（）方法。当应用程序启动时，我将App.cs中的MainPage属性设置为NavigatioService中的navigationPage

问题＃1

通过页面＃1 - ＃3实现导航（在UI导航图上）我使用 SetAndNavigateToRootPage 方法

例如，当用户从第1页INTRO导航到第2页ACCOUNT时。