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How to get the value of the passed parameter of the 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 value of query inside the Filter extension method assigned to _target
574
Func is a delegate that points to a method that accepts one or more arguments and returns a value. Action is a delegate that points to a method which in turn accepts one or more arguments but returns no value. In other words, you should use Action when your delegate points to a method that returns void.
Func<T, TResult> defines a function that accepts one parameter (of type T) and returns an object (of type TResult). In your case, if you want a function that takes a Person object and returns a string...you'd want Func<Person, string> which is the equivalent of: string Function(Person p) { return p.Name; }
C# Func simple example string GetMessage() { return "Hello there!"; } Func<string> sayHello = GetMessage; Console. WriteLine(sayHello()); In the example, we use the Func delegate which has no parameters and returns a single value. This is the function to which we refer with the help of the Func delegate.
If you want to get the parameter you will have to pass expression. By passing a "Func" you will pass the compiled lambda, so you cannot access the expression tree any more.
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
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