这里正确的C#lambda语法是什么？

要使用字符串,您必须使用反射来获取委托;

string searchRulesMethodName = "SearchRules1";
Predicate predicate = (Predicate)
    Delegate.CreateDelegate(typeof(Predicate),
        typeof(Program).GetMethod(searchRulesMethodName));
var results = GetSearchResults(predicate);

当然,switch如果你在编译时知道所有选项,那么会更快更安全!

Predicate predicate;
switch (searchRulesMethodName) {
    case "SearchRules1": predicate = SearchRules1; break;
    case "SearchRules2": predicate = SearchRules2; break;
    default: throw new InvalidOperationException("Unknown filter: "
        + searchRulesMethodName);
}
var results = GetSearchResults(predicate);