Question

我最近一直在为Xamarin.Forms尝试Prism框架，而且我遇到了EventToCommandBehavior的一个问题，我很确定它应该有效。

当我尝试使用NavigationParameters（）将对象从ListView发送到新视图时，它会自动生成为字符串而不是之前发送的对象。

当我尝试将其强制转换为对象时，会出现InvalidCastException。

ListView.cs我通过Navigate（）发送数据到新视图：

private ObservableCollection<Employee> _employeeList = new ObservableCollection<Employee>();
_employeeList.Add("employee", new Employee{ Id = 1, FirstName = "FirstTest", LastName = "LastTest" });

    private async void Navigate()
    {
        var employeePara = new NavigationParameters();
        employeePara.Add("employee", _selectedEmployee);

        await _navigationService.NavigateAsync("EmployeeDetail" + employeePara);
    }

新视图，我尝试将数据作为对象：

private Employee _employee;
public void OnNavigatingTo(NavigationParameters parameters)
{
    try
    {
if (parameters.ContainsKey("employee"))
        _employee = (Employee)parameters["employee"]; // invalid cast happening here
        EmployeeFullName = _employee.FirstName;
    }
    catch (Exception ex)
    {
        throw new Exception(ex.Message);
    }
}

XAML：

  <ContentPage.Resources>
    <ResourceDictionary>
      <c:ItemTappedEventArgsConverter x:Key="itemTappedEventArgs" />
    </ResourceDictionary>
  </ContentPage.Resources>
  <ContentPage.Content>
    <ListView ItemsSource="{Binding EmployeeList}" SelectedItem="{Binding SelectedEmployee}">
      <ListView.Behaviors>
        <b:EventToCommandBehavior
          EventName="ItemTapped"
          Command="{Binding EmployeeTappedCommand}"/>
      </ListView.Behaviors>
      <ListView.ItemTemplate>
        <DataTemplate>
          <TextCell Text="{Binding FullName}" />
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>
  </ContentPage.Content>

Answer 1

Prism for Forms示例也使用类似的方案，但具有不同的NavigateAsync方法签名。我的猜测，你的错了吗？

示例代码await _navigationService.NavigateAsync("RecipePage", p);

示例解决方案https://github.com/PrismLibrary/Prism-Samples-Forms/blob/master/ContosoCookbook/ContosoCookbook/ContosoCookbook/ViewModels/MainPageViewModel.cs#L35

Xamarin.Forms - 将对象传递给新视图的Prism EventToCommandBehavior转换为字符串

1 个答案: