检查类型是浇注料/小类 [英] Check if types are castable / subclasses

问题描述

我有他们作为字符串输入两名成员 - 而不是一个类型的实例。我如何检查两种类型浇注料？比方说串的一个是System.Windows.Forms.Label，另一种是System.Windows.Forms.Control的。如何检查，如果第一个是第二个的子类（或隐式浇注料）？这是可能通过使用反射？

I have they type of two members as strings - and not as a Type instance. How can I check if the two types are castable? Let's say string one is "System.Windows.Forms.Label" and the other one is "System.Windows.Forms.Control". How can I check if the first one is a subclass (or implicit castable) of the second one? Is this possible by using reflection?

感谢您的支持！

推荐答案

这似乎是你应该使用 Type.IsAssignableFrom 但要注意仔细的文档：

It might seem like you should use Type.IsAssignableFrom but note carefully the documentation:

公共虚拟布尔IsAssignableFrom（C型）

真正如果ç 和电流[实例] 键入表示相同的类型，或者如果当前[实例] 键入是的继承层次ç，或者如果电流[实例] 键入是一个接口 C 工具，或者如果 C 是一个泛型类型参数和当前[实例] 键入表示的ç之一。 假如果这些条件都不是真正，或 C 是空引用（没有在Visual Basic中）。

true if c and the current [instance of] Type represent the same type, or if the current [instance of] Type is in the inheritance hierarchy of c, or if the current [instance of] Type is an interface that c implements, or if c is a generic type parameter and the current [instance of] Type represents one of the constraints of c. false if none of these conditions are true, or if c is a null reference (Nothing in Visual Basic).

在特定的：

class Base { }
clase NotABase { public static implicit operator Base(NotABase o) { // } }

Console.WriteLine(typeof(Base).IsAssignableFrom(typeof(NotABase)));

将打印假在控制台上，即使 NotABase 是隐式强制转换为基本秒。因此，要处理铸造，我们可以使用反射像这样：

will print False on the console even though NotABases are implicitly castable to Bases. So, to handle casting, we could use reflection like so:

static class TypeExtensions {
    public static bool IsCastableTo(this Type from, Type to) {
        if (to.IsAssignableFrom(from)) {
            return true;
        }
        var methods = from.GetMethods(BindingFlags.Public | BindingFlags.Static)
                          .Where(
                              m => m.ReturnType == to && 
                                   (m.Name == "op_Implicit" || 
                                    m.Name == "op_Explicit")
                          );
        return methods.Count() > 0;
    }
}

用法：

Usage:

Console.WriteLine(typeof(string).IsCastableTo(typeof(int))); // false
Console.WriteLine(typeof(NotABase).IsCastableTo(typeof(Base))); // true

和你的情况下

// from is string representing type name, e.g. "System.Windows.Forms.Label"
// to is string representing type name, e.g. "System.Windows.Forms.Control"
Type fromType = Type.GetType(from);
Type toType = Type.GetType(to);
bool castable = from.IsCastableTo(to);

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