Func <> getting parameter information

Question

How to get value of passed parameter Func<> Lambda in C #

 IEnumerable<AccountSummary> _data = await accountRepo.GetAsync(); string _query = "1011"; Accounts = _data.Filter(p => p.AccountNumber == _query); 

and this is my extension method

 public static ObservableCollection<T> Filter<T>(this IEnumerable<T> collection, Func<T, bool> predicate) { string _target = predicate.Target.ToString(); // i want to get the value of query here.. , i expect "1011" throw new NotImplementedException(); } 

I want to get the request value inside the filter extension method assigned by _target

Answer 1

If you want to get a parameter, you will need to pass an expression. Skipping "Func" will pass the compiled lambda so that you no longer have access to the expression tree.

 public static class FilterStatic { // passing expression, accessing value public static IEnumerable<T> Filter<T>(this IEnumerable<T> collection, Expression<Func<T, bool>> predicate) { var binExpr = predicate.Body as BinaryExpression; var value = binExpr.Right; var func = predicate.Compile(); return collection.Where(func); } // passing Func public static IEnumerable<T> Filter2<T>(this IEnumerable<T> collection, Func<T, bool> predicate) { return collection.Where(predicate); } } 

Testmethod

 var accountList = new List<Account> { new Account { Name = "Acc1" }, new Account { Name = "Acc2" }, new Account { Name = "Acc3" }, }; var result = accountList.Filter(p => p.Name == "Acc2"); // passing expression var result2 = accountList.Filter2(p => p.Name == "Acc2"); // passing function 

Answer 2

so instead of passing your predicate as Func<T,bool> pass an expression tree instead of Expression<Func<T,bool>

Then you can study the type of expression and get its component parts, this will not affect the way the method is called, you can still pass lambda to it.

Answer 3

I really don't think you can do this. Check the following situation:

Your predicate is Func<T, bool> predicate , so you can call it like this:

 Accounts = _data.Filter(p => true); 

What would you like to receive from such a call?

(p) => true satisfies Func<T, bool> because it takes T as input and returns the value bool .