“does not contain a definition…and no extension me

问题:

I am having an issue whereby I cannot use an objects method because of this error:

Does not contain a definition...and no extension method...

It is very related to this question. I am doing what is given as the answer in that question, but I am still getting this error.

namespace MyProject.ViewModel
{
    public class NetworkHealthViewModel : ViewModelBase
    {
        private IDataService _dataService;
        public ObservableCollection<NetworkBandwidthModel> NbicNetworkBandwidth
        public ObservableCollection<NetworkPortalStatusModel> NbicNetworkPortalStatus

        public NetworkHealthViewModel()
        {
            _dataService = new DataServiceNetworkHealth();
            NbicNetworkBandwidth       = new ObservableCollection<NetworkBandwidthModel>();
            NbicNetworkPortalStatus    = new ObservableCollection<NetworkPortalStatusModel>();
            _dataService.LoadChartItems(NetworkBandwidthLoaded, NetworkBandwidthLoadedFailed);
            _dataService.LoadPortalStatus(NetworkPortalStatusLoaded, NetworkPortalStatusLoadedFailed);
         }

The error lies at LoadPortalStatus(). LoadChartItems() is fine. NetworkBandwidthLoaded and NetworkPortalStatusLoaded are delegates.

NetworkPortalStatusLoaded is laid out pretty much the same as NetworkBandwidthLoaded:

private void NetworkPortalStatusLoaded(IEnumerable<ChartModel> portalStatItems) 
{
    NbicNetworkPortalStatus.Clear();

    var networkPortalItems = from item in portalStatItems
                             where ((NetworkPortalStatusModel)item).Unit == "Portal"
                             select item;

    foreach (var item in networkPortalItems)
    {
        NbicNetworkPortalStatus.Add((NetworkPortalStatusModel)item);
    }

    Message = "Network Portal details loaded";
}

My DataServiceNetworkHealth class is defined as:

namespace MyProject.DataServices
{
    public class DataServiceNetworkHealth : IDataService
    {
        private Action<IEnumerable<ChartModel>> _delagateSuccess;
        private Action<Exception> _delagateFail;
        private String _portalHtmlResponse;

        public void LoadChartItems(Action<IEnumerable<ChartModel>> success, Action<Exception> fail)
        {
          ....
        }

        public void LoadPortalStatus(Action<IEnumerable<ChartModel>> success, Action<Exception> fail)
        {
          ....
        }
    }
}

Method LoadChartItems() is defined in the interface IDataService, but LoadPortalStatus is not. Perhaps that's where the problem lies. There are other DataServiceX classes that do not use LoadPortalStatus.

I know this is a long post, but I thought better to give all info up front. :-) Thanks for any help!

回答1:

Your reference to _dataService is of the type IDataService, which means that you can only access members defined by this interface (or extension methods for said interfae). You mention that LoadPortalStatus isn't part of that interface and thus you cannot access it through the _dataService reference.

Updated based on comment: Let's look at another example. If you define a List<int> reference like this:

List<int> i = new List<int>();

you can access all the members of List<T>() and all the members of Object. However, if you change the reference to

IEnumerable<int> i = new List<int>();

the only accessible members through i are GetEnumerator which is defined on IEnumerable<T> and the members inherited from Object.

If you include the System.Linq namespace, you also get access to the numerous extension methods defined for IEnumerable<T>.

The static type of i determines which members are available through that reference.

回答2:

If LoadPortalStatus is not available in the interface (or an extension method on that interface), then it can't be called from an instance of the interface.

Since you define:

private IDataService _dataService;

This means that you can only access things in _dataService declared in the IDataService (or as an extension method) interface, regardless of what the implementation of that interface is.

So your choices are:

1) make _dataService variable a type that has LoadPortalStatus defined. 2) add LoadPortalStatus to the IDataService interface. 3) Create an extension method for IDataService called LoadPortalStatus

Any of those would work, though 1 or 2 would probably be preferable, in my opinion.

回答3:

Forgive me if I am being stupid, but it looks like you don't have a LoadPortalStatus() method. You do have 2 x LoadChartItems() however.

Copy paste error?

Any chance you could also post the interface code?

回答4:

This might be overly obvious, but could you be getting this error because you don't actually have a LoadPortalStatus method in your code?

You have multiple LoadChartItems methods with identical signatures -- is it possible that one of these is supposed to be the LoadPortalStatus() method?

public void LoadChartItems(Action<IEnumerable<ChartModel>> success, Action<Exception> fail)
{
    ....
}

//Same signature as above - is this supposed to implement LoadPortalStatus??
public void LoadChartItems(Action<IEnumerable<ChartModel>> success, Action<Exception> fail)
{
    ....
}