问题是我似乎无法通过NavigationService传递给ModulesModel，以用于导航到AnotherView项，而我只能将其传递给SectionModel。但我只能将NavigationService传递给父级ListView（我不希望）它需要通过子级ListView。帮助！！！
UI-代码
<ListView
SeparatorColor="Transparent"
VerticalOptions="FillAndExpand"
HorizontalOptions="FillAndExpand"
ItemsSource="{Binding Data}"
HasUnevenRows="True">
<ListView.Header>
<local:ModuleCourseHeaderViewControl />
</ListView.Header>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Frame
HasShadow="False"
BackgroundColor="{StaticResource BiancaBackgroundColour}">
<Frame.CornerRadius>
<OnIdiom
x:TypeArguments="x:Single"
Phone="0"
Tablet="15" />
</Frame.CornerRadius>
<Frame.Margin>
<OnIdiom
x:TypeArguments="Thickness"
Phone="0,10"
Tablet="20,10" />
</Frame.Margin>
<StackLayout>
<Label
FontFamily="{StaticResource LatoRegularFont}"
TextColor="{StaticResource MediumGold}"
Text="{Binding Title}">
<Label.FontSize>
<OnIdiom
x:TypeArguments="x:Double"
Phone="15"
Tablet="17" />
</Label.FontSize>
</Label>
<flv:FlowListView
BackgroundColor="Transparent"
SeparatorVisibility="None"
HasUnevenRows="False"
FlowColumnCount="{DynamicResource ModuleFlowColumnCount}"
RowHeight="{DynamicResource RiseCardHeight}"
FlowItemsSource="{Binding Modules}">
<flv:FlowListView.FlowColumnTemplate>
<OnIdiom
x:TypeArguments="DataTemplate">
<OnIdiom.Phone>
<DataTemplate>
<local:ModuleCourseCardPhoneControl>
<local:ModuleCourseCardPhoneControl.GestureRecognizers>
<TapGestureRecognizer
CommandParameter="{Binding}"
Command="{Binding ItemSelectedCommand}" />
</local:ModuleCourseCardPhoneControl.GestureRecognizers>
</local:ModuleCourseCardPhoneControl>
</DataTemplate>
</OnIdiom.Phone>
<OnIdiom.Tablet>
<DataTemplate>
<local:ModuleCourseCardControl>
<local:ModuleCourseCardControl.GestureRecognizers>
<TapGestureRecognizer
CommandParameter="{Binding}"
Command="{Binding ItemSelectedCommand}" />
</local:ModuleCourseCardControl.GestureRecognizers>
</local:ModuleCourseCardControl>
</DataTemplate>
</OnIdiom.Tablet>
</OnIdiom>
</flv:FlowListView.FlowColumnTemplate>
</flv:FlowListView>
</StackLayout>
</Frame>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
模型-代码
public class NewModuleModel
{
public IList<SectionModel> Sections { get; set; }
public int ActiviyId { get; set; }
public string CourseTitle { get; set; }
}
public class SectionModel
{
public string Title { get; set; }
public IList<ModulesModel> Modules { get; set; }
public INavigationService NavigationService { get; set; }
}
public class ModulesModel
{
public int ModuleId { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public string ModuleImageUrl { get; set; }
public double Progress { get; set; }
public double RoundedProgress
{
get
{
var p = Math.Round(Progress * 100, 0);
return p;
}
}
public DateTime? LastActivityDTUtc { get; set; }
public DateTime? CompletedDate { get; set; }
public string EstimatedDuration { get; set; }
public int AssetCount { get; set; }
public int? NavigationAssetID { get; set; }
public int ActiviyId { get; set; }
public string CourseTitle { get; set; }
public int? NavigationAssetContentType { get; set; }
public string Status
{
get
{
var result = string.Empty;
if (CompletedDate != null)
{
var c = String.Format("{0:d MMMM yyyy}", CompletedDate);
result = "Completed on " + c;
}
else if (LastActivityDTUtc != null)
{
var l = String.Format("{0:d MMMM yyyy}", LastActivityDTUtc);
result = "Last Activity on " + l;
}
else
{
result = "New";
}
return result;
}
}
public ModulesModel()
{
ItemSelectedCommand = new DelegateCommand<ModulesModel>(this.OnCardItemSelectedCommand);
}
private void OnCardItemSelectedCommand(ModulesModel module)
{
if (module.NavigationAssetContentType == 28 && module.AssetCount == 1)
{
var navigationParams = new NavigationParameters();
navigationParams.Add("AssetContentId", module.NavigationAssetID);
navigationParams.Add("AssetActivityId", module.ActiviyId);
navigationParams.Add("AssetModuleId", module.ModuleId);
navigationParams.Add("ParamCourseTitle", module.CourseTitle);
navigationParams.Add("ParamModuleTitle", module.Title);
Preferences.Set("NavFromModulePage", true);
NavigationService.NavigateAsync("AssetWebViewPage", navigationParams, true, false).Forget();
}
else
{
var navigationParams = new NavigationParameters();
navigationParams.Add("ParamModuleId", module.ModuleId);
navigationParams.Add("ParamActivityId", module.ActiviyId);
navigationParams.Add("ParamCourseTitle", module.CourseTitle);
Preferences.Set("NavFromModulePage", false);
//NavigationService.NavigateAsync("ModuleAssetPage", navigationParams, true, false);
}
}
public DelegateCommand<ModulesModel> ItemSelectedCommand { get; set; }
}
}
ViewModel-代码
private async void LoadData()
{
this.ExecuteAsyncTask(async () =>
{
var result = await this.ModuleService.GetNewModuleAsync(ActivityID);
if (result != null)
{
CourseTitle = result.CourseTitle;
CourseDescription = result.CourseDescription;
CourseImageUrl = result.CourseImageUrl;
DurationInSeconds = result.DurationInSeconds;
DurationAsReadableString = result.DurationAsReadableString;
DisplayDescription = result.DisplayDescription;
Progress = Math.Round(result.Progress * 100, 0);
StartDateUTC = result.StartDateUTC;
EnrolmentDate = result.EnrolmentDate;
LastActivityDate = result.LastActivityDate;
foreach (var item in result.Sections)
{
var itemToAdd = new SectionModel
{
Title = item.Title,
Modules = item.Modules,
NavigationService = navigationService
};
Device.BeginInvokeOnMainThread(() =>
{
this.Data.Add(itemToAdd);
});
}
}
else
{
var exception = new Exception($"Api Error");
}
});
}
}
答案 0 :(得分：0)
请记住，MVVM是Model-View-ViewModel。我们经常看到人们将模型和ViewModel混淆。我将通过向您展示适当的架构来间接地回答您的问题。首先，我们将看一个ToDoItem模型。
public class ToDoItem
{
public string Name { get; set; }
public DateTime Created { get; set; }
public DateTime Due { get; set; }
}
有了这个注意事项，我们可以使模型继承自Prism的BindableBase或ReactiveUI的ReactiveObject之类，从而使绑定变得更容易。我将在此假设您已经了解如何使这些属性实现INotifyPropertyChanged。
接下来我们需要的是ViewModel，我们将说这是ToDoItemsPageViewModel
public class ToDoItemsPageViewModel : BindableBase
{
public ObservableCollection<ToDoItem> Items { get; set; }
public DelegateCommand<ToDoItem> ItemSelectedCommand { get; }
private async void ItemSelectedCommandExecuted(ToDoItem item)
{
// do your navigation here..
}
}
最后，我们有了ListView或CollectionView（不推荐使用ListView时应使用它）。为简单起见，让我们看以下内容。
<ListView ItemsSource="{Binding Items}">
<ListView.ItemTemplate>
<DataTemplate>
<StackLayout>
<Label Text="{Binding Name}" />
<Button Text="Show"
Command="{Binding ItemSelectedCommand}"
CommandParameter="{Binding .}" />
</StackLayout>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
这里要理解的核心思想是ListView共享其父Page的BindingContext。在我们的DataTemplate中，我们的BindingContext是ToDoItem，而不是ToDoItemsPageViewModel。结果，我们对Name值的绑定将返回各个ToDoItem的名称。虽然我们对CommandParameter的绑定将在整个ToDoItem中传递，但由于ToDoItem没有这样的命令，因此我们对Command的绑定将不起作用。
现在让我们看看如何从ViewModel中访问Command。
<ListView ItemsSource="{Binding Items}" x:Name="list">
<ListView.ItemTemplate>
<DataTemplate>
<StackLayout>
<Label Text="{Binding Name}" />
<Button Text="Show"
Command="{Binding BindingContext.ItemSelectedCommand,Source={x:Reference list}}"
CommandParameter="{Binding .}" />
</StackLayout>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
我们在这里所做的是三个小的更改。
x:Name添加到ListView。也可以将其放在父页面上。ItemSelectedCommand更改为BindingContext.ItemSelectedCommand Source 这完成的是更新一个特定的绑定以查看父对象。这将BindingContext（针对此单个属性）有效地设置为实际的父级。在这种情况下，您可以将其视为设置为ListView实例的BindingContext。这意味着我们的绑定必须引用BindingContext，然后我们可以在ListView上点进入我们的BindingContext的属性。