System.Linq到GET请求的字符串问题

Question

Why is it when I do this:

    private void button18_Click(object sender, EventArgs e)
    {

        string uri1 = "http://localhost:8000/Service/GetMessage/{anything}";
        string tagUri = uri1.Replace("{anything}", textBox21.Text);
        XDocument xDoc = XDocument.Load(tagUri);
        var MessageID = xDoc.Descendants("Message")
                             .Select(n => new
                             {
                                 MessageID = n.Element("MessageID").Value,
                             })
            .ToString();

        textBox1.Text = MessageID;

I get this really strange output?

System.Linq.Enumerable+WhereSelectEnumerableIterator`2[System.Xml.Linq.XElement,<>f__AnonymousType7`1[System.String]]

But yet when I change ToString to ToList and use:

dataGridView10.DataSource = MessageID;

It displays it correctly? Really struggling to find out a way to take my incoming GET request to string?

Answer 1

Your LINQ query is getting a collection by nature of the call to .Descendants . If there's only one, you can use a .Single() or .First() or .FirstOrDefault() to get the only (or First) item in the list.

Then it would be

textbox1.Text = MessageID.MessageID;

Though you more likely want to do something like this:

var MessageId = xDoc.Element("Message").Element("MessageID").Value;

But I'm somewhat guessing, as I don't know the format or content of your XML.

Answer 2

There are others here who can give you a more detailed explanation, but here's what I think is happening (expanded from my comment above).

By default, LINQ queries return a collection, even when there's only one result. When you call .ToString() on the that collection, you get the fully qualified name of the type of the Object. See Object.ToString Method - which in this case I believe is the weird output you get.

You're probably looking for a single result (MessageID), so you could use .FirstOrDefault() instead of .ToString() , like this:

var MessageID = xDoc.Descendants("Message")
                .Select(n => new
                {
                    MessageID = n.Element("MessageID").Value,
                })
                .FirstOrDefault();

Note that n.Element("MessageID").Value will return a string, which you can then assign to the TextBox.

When you convert the query to a List, you are able to bind it to the DataGridView's DataSource because DataSource takes objects that implement one of the IList interfaces ( IList in the case of a generic list).