wpf 无法使用实体框架 6 将 void 分配给隐式类型的局部变量

Cannot assign a void to an implicitly-typed local variable using Entity Framework 6

提问by CareTaker22

I am using a WCF refrenceto call the last row from my Quotetable. Now I wrote this method in my WCF application to get the last row, but I do not know it it works or not(I am trying to test it):

我正在使用WCF 引用来调用Quote表中的最后一行。现在我在我的 WCF 应用程序中编写了这个方法来获取最后一行，但我不知道它是否有效（我正在尝试测试它）：

public void GetLastQuote()
{
    using (TruckDb db = new TruckDb())
    {
        var quote = (from qData in db.Quotes
                     where qData.Id == qData.RepresetativeId
                     orderby qData.Id descending
                     select qData).First();
    }
}

In my WPF application I am using the WCF reference and calling on the GetLastQuoteAsync()method, but it is giving me the following error:

在我的 WPF 应用程序中，我正在使用 WCF 引用并调用该GetLastQuoteAsync()方法，但它给了我以下错误：

Cannot assign void to an implicitly-typed local variable

不能将 void 分配给隐式类型的局部变量

And here is the method in my WPF application where I am trying to call the GetLastQuoteAsync()reference.

这是我尝试调用GetLastQuoteAsync()引用的WPF 应用程序中的方法。

private async void wListOfBills_Loaded(object sender, RoutedEventArgs e)
{
    using (TruckServiceClient client = new TruckServiceClient())
    {
        var quote = await client.GetLastQuoteAsync(); // -> This is where the error lies.
        var bills = await client.GetListOfBillsAsync(quote.Item.Id);
        if (bills == null)
        {
            dgFloor.IsEnabled = true;
            return;
        }
        dgFloor.ItemsSource = bills.Select(x => new ListOfBillsView
        {
            Code = x.StockCode,
            Group = x.GroupName,
            Description = x.StockDescription,
            Qty = x.Quantity,
            Length = x.Length,
            Width = x.Width,
            Weight = x.Weight,
            Price_m = x.PricePerMeter,
            Cost = x.Cost,
            Section = x.TruckSection.ToString()
        }).ToList();
    }
}

I have seen some people with the same question, but I do not fully understand how to implement the solutions in my own problem. If anyone could help, I would appreciate it allot! :)

我见过一些人提出同样的问题，但我不完全了解如何在我自己的问题中实施解决方案。如果有人可以提供帮助，我将不胜感激！:)

回答by Marco

You want to call what your query is returning, but the method wrapping around that query is returning nothing, because its type is void.

您想调用查询返回的内容，但环绕该查询的方法不返回任何内容，因为它的类型为 void。

I assume you want to return an object of type Quote, so you need to change your method to this:

我假设您想返回一个 type 对象Quote，因此您需要将方法更改为：

//change from void to Quote
public Quote GetLastQuote()
{
    using (TruckDb db = new TruckDb())
    {
        var quote = (from qData in db.Quotes
                     where qData.Id == qData.RepresetativeId
                     orderby qData.Id descending
                     select qData).First();
        //new
        return quote;
    }
}

Also GetLastQuote()is not the same as GetLastQuoteAsync()Have you posted the wrong method, which would throw the same error?

同样GetLastQuote()是不一样的GetLastQuoteAsync()你贴错了方法，它会抛出同样的错误？

If there is also async version of this method it should probably look similar to this:

如果此方法也有异步版本，它可能看起来类似于：

public async Task<Quote> GetLastQuote()
{
    using (TruckDb db = new TruckDb())
    {
        var quote = (from qData in db.Quotes
                     where qData.Id == qData.RepresetativeId
                     orderby qData.Id descending
                     select qData).FirstAsync(); /*Note async method here*/
        //new
        return await quote;
    }
}