Question

在我的WPF MVVM应用程序的视图模型和数据模型下面。我在执行调用时遇到问题（见下文），抛出异常参数计数不匹配。方法“getDataFromDatabase”返回“UserData”的集合。那么如何解决这个问题？

查看模型：

public class MyViewModel : BaseViewModel
{
    private static Dispatcher _dispatcher;
    public ObservableCollection<UserData> lstUsers

    public ObservableCollection<UserData> LstUsers
    {
        get
        {
            return this.lstUsers;
        }

        private set
        {
            this.lstUsers= value;
            OnPropertyChanged("LstUsers");
        }
    }

    // LoadData is called from the constructor of the view code-behind (xaml.cs) once DataContext is correctly set.
    public void LoadData()
    {
        ThreadPool.QueueUserWorkItem(new WaitCallback((o) =>
        {
            var result = getDataFromDatabase();
            UIThread((p) => LstUsers = result);
        }));
    }

    ObservableCollection<UserData> getDataFromDatabase()
    {            
        return this.RequestDataToDatabase();
    }

    static void UIThread(Action<object> a)
    {
        if(_dispatcher == null) 
        {
           _dispatcher = Dispatcher.CurrentDispatcher;
        }

        _dispatcher.Invoke(a); <---- HERE EXCEPTION IS THROWN
    }
}

数据模型：

public class UserData
{
   public string ID{ get; set; }
   public string Name { get; set; }
   public string Surname { get; set; }

   // Other properties
}

Answer 1

Action<object>是一个参数类型为对象的Action。它必须通过Invoke(Delegate method, params object[] args)重载使用单个参数调用：

Application.Current.Dispatcher.Invoke(a, someObject);

所以将Action<object>更改为Action：

static void UIThread(Action a)
{
    Application.Current.Dispatcher.Invoke(a);
}

并将其称为：

UIThread(() => LstUsers = result);

您可能还想让LoadData方法异步并按如下方式编写：

public async Task LoadData()
{
    await Task.Run(() =>
    {
        var result = getDataFromDatabase();
        Application.Current.Dispatcher.Invoke(() => LstUsers = result);
    });
}

TargetParameterCountException：参数计数不匹配

1 个答案: