如何将 Class 公共属性设置为类型列表<t> ?</t>

Question

I want to define a public property in a User Control with a type of List that I can pass a List to and then have the control bind it to a repeater.

public partial class RepeaterPager : System.Web.UI.UserControl
{
    public List<T> DataSource;
}

The from calling code

List<someClass> list = new List<someClass>;
RepeaterPager1.DataSource = list ;

I thought this would be simple, but I am getting Error The type or namespace name 'T' could not be found (are you missing a using directive or an assembly reference?) on the line that declares the public property. What am I doing wrong

Cheers

Stewart

Answer 1

This is only possible if the class containing property is generic. In theory, you could use generic method:

void SetDataSource<T>(List<T> dataSource)

but you'll lose type information elsewhere.

Maybe,

IEnumerable DataSource

will be a better option?

Answer 2

You can't have generic parameters in fields of a class with out the class being generic.

See this answer for info on making a usercontrol generic: C# generics usercontrol

Or you could just use a non-generic version, such as IEnumerable or IList .

Answer 3

You either need to define generic Type, or make RepeaterPager generic

public partial class RepeaterPager<T> : System.Web.UI.UserControl
{
    public List<T> DataSource;
}

Answer 4

The general pattern for this type of data binding is to define DataSource as type object. Then, in the set method you can do a runtime check to verify the object is of a type you expect -- throw an exception or debug assert otherwise.

Besides, Repeater.DataSource is type object anyways...

Many times I can get away without holding a reference to the datasource, so I pass it directly to the control:

public object DataSource
{
    get { return myRepeater.DataSource; }
    set {
        if (value is IEnumerable) // or whatever your requirement is, if needed
            myRepeater.DataSource = value;
        else
            throw new NotSupportedException("DataSource must be an IEnumerable type");
    }
}

However, if you really do need to know about the type T, I would consider the following:

1. If possible, use the generic class idea others have suggested.
2. If you need to repeat this pattern for different classes, build a base class or Interface for all your data sources to derive from
3. Use DataSource as type object, but just grab the type at run time using obj.GetType() . (Depending on your needs this may or may not work)