Silverlight异常中的LINQ to SQL [英] LINQ to SQL in silverlight exception

问题描述

这是我上一个问题的延续:

This is a continution of my previous question: Could not find an implementation of the query pattern

现在，我设法查询数据库，但似乎无法在网页上获取内容.

Now I managed to query my database I can't seem to get the content on my webpage.

我尝试使用以下代码返回代码:

I try to return the code using the following code:

private void button1_Click(object sender, RoutedEventArgs e)
{
    Service1Client client = new Service1Client();

    client.GetPersoonByIDCompleted += new EventHandler<GetPersoonByIDCompletedEventArgs>(client_GetPersoonByIDCompleted);
    client.GetPersoonByIDAsync("1");
}

void client_GetPersoonByIDCompleted(object sender, GetPersoonByIDCompletedEventArgs e)
{
    if (e.Error != null)
        textBox1.Text = e.Error.ToString();
    else
        label1.Content = e.Result.Voornaam.ToString();
}

但是，当我按下按钮时，出现以下错误:

However when I press the button I get the following errors:

对象引用未设置为对象的实例.

Object reference not set to an instance of an object.

在 SilverlightApplication1.MainPage.client_GetPersoonByIDCompleted(Object 发送者，GetPersoonByIDCompletedEventArgs e)位于 SilverlightApplication1.ServiceReference1.Service1Client.OnGetPersoonByIDCompleted(Object 状态)

at SilverlightApplication1.MainPage.client_GetPersoonByIDCompleted(Object sender, GetPersoonByIDCompletedEventArgs e) at SilverlightApplication1.ServiceReference1.Service1Client.OnGetPersoonByIDCompleted(Object state)

奇怪的是，当我不使用LINQ而是使用普通的SQL时，它可以正常工作.

The weird thing is it works when I do not use LINQ, but normal SQL.

    string sql = "SELECT ID, naam, voornaam, leeftijd FROM tblPersoon WHERE id=@pmID";
    Persoon pers = null;
    string connstr = ConfigurationManager.ConnectionStrings["connDB"].ConnectionString;

    using (SqlConnection cn = new SqlConnection(connstr))
    {
        SqlCommand com = new SqlCommand(sql, cn);
        com.Parameters.AddWithValue("pmID", id);
        cn.Open();
        SqlDataReader reader = com.ExecuteReader();
        if (reader.Read())
        {
            pers = new Persoon();
            pers.ID = reader.GetString(0);
            pers.Naam = reader.GetString(1);
            pers.Voornaam = reader.GetString(2);
            pers.Leeftijd = reader.GetInt32(3);
        }
    }

    return pers;
}

LINQ结果:

SQL结果:

感谢您的帮助，我非常感谢！ 托马斯

Thank you for helping me, I grealy appreciate it! Thomas

推荐答案

通过在无效的情况下尝试引用"e.Result"属性(即，当方法调用返回异常而不是a)时，获得该特定异常.价值.在引用e.Result之前，请确认e.Error == null，如果没有，请沉迷于一些错误处理或消息传递代码，例如:

You get that particular exception by trying to reference the "e.Result" property when it's not valid, i.e., when the method call returned an exception instead of a value. Before you reference e.Result, confirm that e.Error == null, and if it doesn't, indulge yourself in some error handling or messaging code, e.g.:

void client_GetPersoonByIDCompleted(object sender, GetPersoonByIDCompletedEventArgs e)
{
    if (e.Error != null)
    {
        MessageBox.Show("An error occurred: " + e.Error.ToString());
    }
    else
    {
        label1.Content = e.Result;
    }
}

或类似的东西.

这篇关于Silverlight异常中的LINQ to SQL的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！