使用绑定从 CollectionView 的 ItemTemplate 调用时不会触发命令

Question

我在使用绑定从 ViewModel 导航时遇到问题，命令异步方法 OnMovieClicked 根本不会触发。

public class MainViewModel : BaseViewModel
    {
        private List<Movie> popularMovies;
        public List<Movie> PopularMovies
        {
            get => popularMovies;
            set => SetProperty(ref popularMovies, value);
        }

        public ICommand NavigateToMovieCommand { get; set; }

        private readonly TMDBService tmdbService;
        private readonly INavigationService navigationService;

        public MainViewModel()
        {
            tmdbService = new TMDBService();
            navigationService = new NavigationService();

            NavigateToMovieCommand = new Command<int>(async (id) => await OnMovieClicked(id));

            InitAsync();
        }

        private async void InitAsync()
        {
            PopularMovies = await tmdbService.GetPopularMovies();
        }

        private async Task OnMovieClicked(int id)
        {
            Console.WriteLine("****Navigate");
            var viewModel = new MovieViewModel(id);
            await navigationService.PushAsync(new MoviePage(viewModel));
        }

它没有向控制台写入任何内容，我已经测试了我的导航服务并且它工作正常

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:viewmodels="clr-namespace:MovieApp.ViewModels"
             Title="New Releases"
             x:Class="MovieApp.MainPage"
             x:Name="MoviePage"
             BackgroundColor="DarkSlateGray">

    <ContentPage.BindingContext>
        <viewmodels:MainViewModel/>
    </ContentPage.BindingContext>

    <CollectionView ItemsSource="{Binding PopularMovies}"
                    SelectionMode="None"
                    ItemSizingStrategy="MeasureAllItems"
                    ItemsLayout="VerticalGrid, 3">
        <CollectionView.ItemTemplate>
            <DataTemplate>
                <ContentView>
                    <Frame HasShadow="True"
                           Margin="10"
                           WidthRequest="80"
                           BackgroundColor="LightSlateGray"
                           Padding="0"
                           CornerRadius="15">

                        <Grid RowDefinitions="120,25">

                            <Image Aspect="AspectFill"
                                    Source="{Binding PosterPath}"
                                    Grid.RowSpan="2"/>

                            <BoxView WidthRequest="80"
                                   Grid.Row="1"
                                   Opacity="0.85"
                                   BackgroundColor="LightSlateGray"/>

                            <Label Grid.Row="1"
                                    TextColor="White"
                                    HorizontalOptions="CenterAndExpand"
                                    Padding="8,0"
                                    Text="{Binding Title}"
                                    LineBreakMode="TailTruncation"/>

                           <Button Grid.RowSpan="2"
                                   BackgroundColor="Blue"
                                   Command="{Binding BindingContext.NavigateToMovieCommand, Source={x:Reference MoviePage}}"
                                   CommandParameter="{Binding Id}"/>
                        </Grid>
                    </Frame>
                </ContentView>
            </DataTemplate>
        </CollectionView.ItemTemplate>
    </CollectionView>
</ContentPage>

我已经将 x:Name 和 x:Reference 属性添加到页面和命令

我不认为我在 XAML 文件中做错了什么，但这一定是一个有约束力的问题，因为它不会将日志行打印到控制台。

更新：

这是电影模型

    public partial class Movie
    { 
        [JsonProperty("id")]
        public long Id { get; set; }

        [JsonProperty("poster_path")]
        public string PosterPath {
            get;
            set;
        }

        [JsonProperty("release_date")]
        public string ReleaseDate { get; set; }

        [JsonProperty("title")]
        public string Title { get; set; }

        [JsonProperty("vote_average")]
        public double VoteAverage { get; set; }

        [JsonProperty("credits", NullValueHandling = NullValueHandling.Ignore)]
        public Credits Credits { get; set; }
    }

Answer 1

你的代码没问题，没有问题，但是你没有post一些关于Movie的代码，Id property类型是int或string，如果 Movie class Id property 是 string，传递 Id 参数作为 int 输入 NavigateToMovieCommand，命令不会开火。

 NavigateToMovieCommand = new Command<int>(async (id) => await OnMovieClicked(id));

我用下面的Movieclass，设置Id属性类型为int，用你的代码测试，Buttom命令可以解雇了，没问题。

public class Movie
{
    public int Id { get; set; }
    public string PosterPath { get; set; }
    public string Title { get; set; }
}

使用绑定从 CollectionView 的 ItemTemplate 调用时不会触发命令

Command is not triggered when called from CollectionView's ItemTemplate using Binding

navigation

data-binding

mvvm

xamarin.forms