C# 是否可以通过 LINQ 子句将 orderby 抽象为 function 参数？

Question

I have an ObservableCollection Bound to a WPF List View. I am looking to be able to sort the columns of the ListView control by clicking on the Column Header. To do this I am sorting the ObservableCollection and letting the binding take care of updating the GUI.

To sort the ObservableCollection I am using the following code:

sortedData = new ObservableCollection<Tag>( from x in data
                                            orderby x.ID descending
                                            select x );
data = sortedData;

NB: data is bound to the ListView

The problem I'm having is that for each of the columns there would be a lot of copy-paste code to achieve the desired effect. Is it possible to pass the 'orderby x.ID descending' portion of the LINQ statement as a function parameter?

Or is there an entirely easier way to achieve the desired result?

Answer 1

You could use a Func as a method parameter containing a lambda expression.

If you want to order every single type by it's ID you could specify an interface on all of those types too and use a generic method.

For example

public ObservableCollection<Tag> Sort(Func<ObservableCollection<Tag>> sortFunc)  
{  
    //do something else  
    data = sortFunc();  
    //do something else  
}

which can be called like

Sort(list.OrderByDescending(x => x.ID));

in which list is your ObservableCollection.

Answer 2

You define a sort function like this:

Func<Tag, int> sortFunc = x => -x.ID;

(Sorting by negative ID has the same effect as sorting by ID descending.)

You can then apply this sort function to any IEnumerable<Tag> :

var sortedData = new ObservableCollection<Tag>(data.OrderBy(sortFunc));

Answer 3

The way I managed to achieve this was with thekip's idea of passing a Func into the function eg

sortColumn( "ID", x => x.ID );

protected void sortColumn<T>( string name, Func<Tag, T> selector )
{
    ObservableCollection<Tag> sortedData = new ObservableCollection<Tag>( TagData.OrderBy( selector ) );

    data = sortedData;
}

Answer 4

You can use Dynamic Query.It will composing LINQ statements on the fly, dynamically, at run time.

For example:

var query =
           db.Customers.Where("City == @0 and Orders.Count >= @1", "London", 10).
           OrderBy("CompanyName").
           Select("New(CompanyName as Name, Phone)");

You can get it here: http://code.msdn.microsoft.com/DynamicQuery-f65f6a4d

Answer 5

I think you are looking for Dynamic Linq.

See if these sample helps:-

http://msdn.microsoft.com/en-gb/bb737920.aspx

http://msdn.microsoft.com/en-gb/bb737920.aspx

Answer 6

You can use Dynamic Linq for this

whith it you can write something like:

var sortExpr = "x.ID";

IQueryable<Tag> sortedQuery = query.OrderBy(sortExpr);