Cast an Anonymous Types in Object and retrieve one Field

问题

I use C# asp.net4.

I have a method to populate a Repeater with Anonymous Types (Fields: Title, CategoryId), inside the Repeater I also placed a Label:

        var parentCategories = from c in context.CmsCategories
                               where c.CategoryNodeLevel == 1
                               select new { c.Title, c.CategoryId };
        uxRepeter.DataSource = parentCategories;
        uxRepeter.DataBind();

I need to change Text Properties for each label inside my Repeater on Repeater Event ItemDataBound

   protected void uxRepeter_ItemDataBound(object sender, RepeaterItemEventArgs e)
    {
        HyperLink link = (HyperLink)e.Item.FindControl("uxLabel");
        uxLabel.Text = // How to do here!!!!!!!! 
    }

So I need set the properties for Label.Text using e.Item (or a better way if any).

My problem I'm not able to CAST the e.Item (Anonymous type Field Title) and set it as Text Propriety for my Label.

I understand Anonymous Type can be casted to only Object Type, but in my case my Anonymous Type has Title and CategoryId Fields.

My question:

How to cast and retrieve the field with I'm interested? Thanks for your time on this?

EDIT: SOME ERROR I RECEIVE:

Unable to cast object of type '<>f__AnonymousType0`2[System.String,System.Int32]' to type 'System.String'.

回答1:

The options Joseph presents are good ones, but there is a horrible way you can do this. It's somewhat fragile, as it relies on you specifying the anonymous type in exactly the same way in two places. Here we go:

public static T CastByExample<T>(object input, T example)
{
    return (T) input;
}

Then:

object item = ...; // However you get the value from the control

// Specify the "example" using the same property names, types and order
// as elsewhere.
var cast = CastByExample(item, new { Title = default(string),
                                     CategoryId = default(int) } );
var result = cast.Title;

EDIT: Further wrinkle - the two anonymous type creation expressions have to be in the same assembly (project). Sorry for forgetting to mention that before now.

回答2:

You can't cast the anonymous type to anything because you literally have no type to cast it to, as you've basically pointed out already.

So you really have two options.

Don't cast to an anonymous type, but rather a known type that you build just for handling this scenario or
assign a dynamic variable to the item and use dynamic properties instead

Example 1:

var parentCategories = from c in context.CmsCategories
    where c.CategoryNodeLevel == 1
    select new RepeaterViewModel { c.Title, c.CategoryId };

Example 2: (also I think you're last line you meant to assign the link var)

protected void uxRepeter_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
    HyperLink link = (HyperLink)e.Item.FindControl("uxLabel");
    dynamic iCanUseTitleHere = e.Item;
    link.Text = iCanUseTitleHere.Title; //no compilation issue here
}

回答3:

You can use a dynamic in this case. I think the code would be:

protected void uxRepeter_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
    dynamic link = (dynamic)e.Item.FindControl("uxLabel");
    uxLabel.Text = link.Title; //since 'link' is a dynamic now, the compiler won't check for the Title property's existence, until runtime.
}

回答4:

Can't you just cast to (typeof(new { Title = "", CategoryID = 0 }))?

来源：https://stackoverflow.com/questions/6901506/cast-an-anonymous-types-in-object-and-retrieve-one-field

标签

ASP.NET

repeater

anonymous-types