使用参数调用 expression.call 中的静态方法

Question

我已经为 Contains 方法扩展了字符串 class。我试图在 Expression.Call 中调用它，但如何正确传递参数？

代码：字符串包含方法：

public static class StringExts
{
    public static bool NewContains(this string source, string ValToCheck, StringComparison StrComp)
    {
        return source.IndexOf(ValToCheck, StrComp) >= 0;
    }
}

在表达式调用中：

public class Person { public string Name {get; set;} }

public class Persons { 
    public List<Person> lstPersons {get; set;} 
    public Persons() {
      lstPersons = new List<Person>();    
    }
}

public class Filter 
{
    public string Id { get; set; }
    public Operator Operator { get; set; }
    public string value { get; set; }
}

public void Main()
{
   //Get the json.
   //"Filters": [{"id": "Name", "operator": "contains", "value": "Microsoft"}]

    Filter Rules = JsonConvert.DeserializeObject<Filter>(json);

   // Get the list of person firstname.
    List<Person> lstPerson = GetFirstName();

   ParameterExpression param = Expression.Parameter(typeof(Person), "p");
   Expression exp = null;

   exp = GetExpression(param, rules[0]);

   //get all the name contains "john" or "John"
   var filteredCollection = lstPerson.Where(exp).ToList();

}

private Expression GetExpression(ParameterExpression param, Filter filter){
   MemberExpression member = Expression.Property(param, filter.Id);
   ConstantExpression constant = Expression.Constant(filter.value);

   Expression bEXP = null;

   switch (filter.Operator)
    {
         case Operator.contains:
           MethodInfo miContain = typeof(StringExts).GetMethod("NewContains", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
           return  Expression.Call(miContain, member, constant , Expression.Constant(StringComparison.OrdinalIgnoreCase));; 
           break;
    }
 }

错误：

An unhandled exception of type 'System.ArgumentException' occurred in System.Core.dll.Additional information: Static method requires null instance, non-static method requires non-null instance.

下面的Call()方法如何调用miContain中的参数？

我已经更新了代码。

Answer 1

您没有指定足够的参数（2 对 3）。 NewContains 有三个参数。

此外，由于此方法不是实例方法，因此您无法设置此参数。 This overload looks better.

您可能应该检查 overload list。这就是我如何在事先不知道的情况下找到这个问题的正确答案。

Answer 2

您没有指定所有参数。如果您为所有人创建表达式，它会起作用：

ParameterExpression source = Expression.Parameter(typeof(string));
string ValToCheck = "A";
StringComparison StrComp = StringComparison.CurrentCultureIgnoreCase;

MethodInfo miContain = typeof(StringExts).GetMethod("NewContains", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
var bEXP = Expression.Call(miContain, source, Expression.Constant(ValToCheck), Expression.Constant(StrComp));

var lambda = Expression.Lambda<Func<string, bool>>(bEXP, source);

bool b = lambda.Compile().Invoke("a");

使用参数调用 expression.call 中的静态方法

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