我已经在 wpf 中实现了 MVVM 模式。但是结果没有显示在视图中。有人可以帮帮我吗？

Question

使用 getAllCars() 函数，我从后端 webapi 获取所有汽车，并将它们保存在 ObservableCollection Cars 中。当我运行应用程序时，它确实显示任何 data.I 不知道为什么数据没有显示，请任何人帮忙？...................... ..................................................... ..................................................... ..................................................... ..................................................... ..................................................... ..................................................... ..................................................... ..................................................... ..................................................... .........

MainWindow.xaml

image of window

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:CarsUIWpfApp"
        xmlns:ViewModels="clr-namespace:CarsUIWpfApp.ViewModels" x:Class="CarsUIWpfApp.MainWindow"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800"
        WindowStartupLocation="CenterScreen">

        <ListView Margin="10" Name="carsList" ItemsSource="{Binding Cars}">
            <ListView.DataContext>
                <ViewModels:CarViewModel/>
            </ListView.DataContext>
            <ListView.View>
                <GridView>
                    <GridViewColumn Header="CarBrand" Width="auto" DisplayMemberBinding="{Binding CarBrand}" />
                    <GridViewColumn Header="CarModel" Width="auto" DisplayMemberBinding="{Binding CarModel}" />
                    <GridViewColumn Header="CarVin" Width="auto" DisplayMemberBinding="{Binding CarVin}" />
                    <GridViewColumn Header="Color" Width="auto" DisplayMemberBinding="{Binding Color}" />
                </GridView>
            </ListView.View>
        </ListView>

    </Grid>
</Window>

MainWindow.xaml.cs

 public partial class MainWindow : Window

    {

        public MainWindow()
        {
            InitializeComponent();
        }
    }

CarViewModel

class CarViewModel : INotifyPropertyChanged
{
    private const string path = "https://localhost:44363/api/Cars";
   private ObservableCollection<Car> cars = new ObservableCollection<Car>();


    public CarViewModel()
    {
        LoadCars();
    }
    public ObservableCollection<Car> Cars
    {
        get { return cars; }
        set { SetProperty<ObservableCollection<Car>>(ref cars, value);
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public async void LoadCars()
    {
        Cars = await getAllCars();
    }

    public async Task<ObservableCollection<Car>> getAllCars()
    {
        

        using (HttpClient client = new HttpClient())
        {
            HttpResponseMessage response = await client.GetAsync(path);

            cars = await response.Content.ReadAsAsync<ObservableCollection<Car>>();
            return cars;
        }

    }

}

Debuging image

Answer 1

您不得在视图模型中声明和调用 async void 方法。

声明为async Task

public async Task LoadCars()
{
    Cars = await getAllCars();
}

并从视图模型构造函数中删除调用，或者删除整个 CarViewModel 构造函数。

然后在视图中，将 DataContext 分配移动到 MainWindow 并附加一个异步 Loaded 事件处理程序：

<Window ... Loaded="WindowLoaded">
    <Window.DataContext>
        <ViewModels:CarViewModel/>
    </Window.DataContext>
    ...
</Window>

在 MainWindow.xaml.cs 中使用此处理程序方法：

private async void WindowLoaded(object sender, RoutedEventArgs e)
{
    await ((CarViewModel)DataContext).LoadCars();
}

另请注意，Cars 不需要是 ObservableCollection，只要您只创建和分配完整的集合，并且从不在现有 Cars 集合中添加或删除元素。

Answer 2

<ListView.DataContext>
      <ViewModels:CarViewModel/>
</ListView.DataContext>

这样做意味着列表视图将此 viewModel 作为数据上下文，但在您的项目源中您绑定到汽车集合，因此解决方案是这样做：

<Window.DataContext>
      <ViewModels:CarViewModel/>
</Window.DataContext>

我已经在 wpf 中实现了 MVVM 模式。但是结果没有显示在视图中。有人可以帮帮我吗？

I have implemented MVVM pattern in wpf. But the result doesnt showed in the view. Can some one please help me?

c#

wpf

mvvm

async-await

MainWindow.xaml

MainWindow.xaml.cs

CarViewModel