在这种情况下如何从asp.net的下拉控件中获取价值？

Question

My scenario is this: I have asp.net page which having the drop down control with Product list. in database my Product Table has fields as ProductId, Product Name and Price. where as I have filled this drop down control by this method:

   private void FillProducts()
            {

            List<Product> productList = objProductManager.GetProducts();
            if (productList.Count > 0)
                {
                drpProducts.DataSource = productList;
                drpProducts.DataTextField = "ProductName";
                drpProducts.DataValueField = "ProductId";

                drpProducts.DataBind();
                }
            }

Which is working perfect. But i want to get selected product Price value on client side. for that I don't want round trip at server to get that. is any property of dropdown control other than DataTextFeild Or DataValueField to hold the Price Field of product ? so that i would avoid to go back at server. Or suggest any remedy for the same. Please guide me.

Answer 1

That's where Global variables and Session Variables takes place...

In a Web Environment you can have both , a Global Variable for cross users (where you can have the entire product list cached) or in a Session variable that you can use for only that user session.

You method would look like:

public MyPMan objProductManager = new MyPMan();

public List<Product> ProductList 
{
    get
    {
        if(Session["MyApp-ProductList"] == null)
            Session["MyApp-ProductList"] = objProductManager.GetProducts();
        return (List<Product>)Session["MyApp-ProductList"];
    }
}

private void FillProducts()
{

    //List<Product> productList = objProductManager.GetProducts();
    if (this.ProductList.Count > 0)
    {
        drpProducts.DataSource = this.ProductList;
        drpProducts.DataTextField = "ProductName";
        drpProducts.DataValueField = "ProductId";

        drpProducts.DataBind();
    }
}

and you can easily, on submit or anything, just grab the price as

double p = this.ProductList.Where(x => x.ID.Equals(12)).Price;

This way, you only query the DB once per session, and it's available across the website, my suggestion is that you create a Static Business Object to be available every where and simply :)

then for example, you would do this as the first line

if (MyStaticObject.ProductList.Count > 0)

if you want to have the Product list across sessions and users, use the Application variable and set that in global.asax file.

---

added

How to do client validation using this:

I love jQuery Validation as it's the easiest and a fantastic client validation tool, so cool that even Microsoft now uses on ASP.NET MVC 2 and more in MVC3 ;)

you can easily pass values from ASP.NET into Javascript as

var myJavaScriptVariable = '<%= myAspVariable %>';

the other way around is more tricky ;)

and you can easily pass a JSON and use that JSON string, I would suggest Json.NET

Or you can use the built-in validation in ASP.NET WebForms... please provide what are you doing in your form (Repeater, GridView, List) in order to give you the exact code.

---

added (part 2)

to convert your Product List into a Json Array in javascript, you can do this:

in ASP.NET MVC 3

var jsonMVC = @Html.Raw(Json.Encode(reg));

in ASP.NET WebForms (using JSon.NET)

var jsonWebForms = <%= Newtonsoft.Json.JsonConvert.SerializeObject(MyStaticObject.ProductList) %>;

and then you can easily access all your object, for example:

var product = jsonMVC[0];
alert(product.Price);

There are more techniques, but I hope this ones helps.

Remember, I still strongly suggest that you use the built-in ASP.NET Control Validation, as you will have that out of the box, if you using a gridview use the RowDataBound Event to build up your stuff.

Answer 2

I would prefer an ajax solution here. Alternatively to Microsoft own UpdatePanel, an javascript/ajax/json call that sends the selected value in dropbox back to the server without reloading.

Answer 3

一般而言，在任何Web应用程序中解决此问题的一种直接方法是在页面中包含[ProductId，ProductPrice]数组，与下拉列表无关，并在客户端JavaScript中与您当前的ProductId结合使用值。

Answer 4

You could always include a second dropdown which contains the ProductID-Price relation and hide is using css.

It would be as though you have a master-child table relation but with two dropdowns. The it's only a question of manipulating the dropdowns with, say, jQuery