Question

我有ViewModel注入构造函数（Prism）。

public class MainPageViewModel : ViewModelBase, IIncrementalSource<Tender>
{
    public async Task<IEnumerable<Tender>> GetPagedItemsAsync(int pageIndex, int pageSize, CancellationToken cancellationToken = default(CancellationToken))
    {
        TendersRequest.Offset = pageIndex;
        TendersRequest.Count = pageSize;
        return await _dataService.GetTenders(TendersRequest);
    }


     public MainPageViewModel(IUnityContainer container, IDataService dataService)
     {
         ... 

         var Tenders = new IncrementalLoadingCollection<MainPageViewModel, Tender>(10);
     }
}

但是Tenders = new IncrementalLoadingCollection（10）;抛出System.InvalidOperationException。

An exception of type 'System.InvalidOperationException' occurred in Microsoft.Toolkit.Uwp.dll but was not handled in user code

Additional information: TSource must have a parameterless constructor

我做错了什么？如何使用IncrementalLoadingCollection和自定义构造函数？

Answer 1

如果你打电话给new IncrementalLoadingCollection<MainPageViewModel, Tender>(10)，那么这个集合会尝试创建一个MainPageViewModel的新实例，只有当它有一个无参数构造函数时才有效（这显然不是你的情况））。解决方法是提供您自己的MainPageViewModel实例：

 public MainPageViewModel(IUnityContainer container, IDataService dataService)
 {
     ... 

     var Tenders = new IncrementalLoadingCollection<MainPageViewModel, Tender>(this, 10);
 }

使用自定义构造函数的IncrementalLoadingCollection和ViewModel

1 个答案: