FUNC<>获取参数信息 [英] Func<> getting the parameter info

问题描述

如何让 Func键1所述的传递参数的值;> LAMBDA在C＃

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);

这是我的扩展方法

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();
}

我想获得的查询值里面分配到 _target

推荐答案

如果你想获得你将不得不参数过滤器扩展方法通过表情。通过传递一个FUNC你会通过编译拉姆达，所以你不能访问表达式树了。

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的

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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