C# 反射程式設計實戰：動態載入、型別檢視與方法調用完整範例

反射核心應用場景

• 外掛架構動態載入組件與型別
• 序列化/反序列化引擎
• ORM 框架實體映射
• 單元測試框架自動發現測試方法
• 依賴注入容器型別掃描與實例化

完整示範程式

using System;
using System.Reflection;
using System.Reflection.Emit;

public class TestReflection {
    private string file = @"TestReflection.exe";

    static void Main(string[] args) {
        TestReflection test = new TestReflection();
        test.DisplayModules();
        test.DisplayTypes();
        test.DisplayMethods();
        test.InvokeStaticMethod();
        test.InvokeMethod();
    }

    // 顯示所有模組
    public void DisplayModules() {
        Console.WriteLine("display modules ...");
        Assembly assembly = Assembly.LoadFrom(file);
        foreach (Module module in assembly.GetModules())
            Console.WriteLine("module name: " + module.Name);
    }

    // 顯示所有型別
    public void DisplayTypes() {
        Console.WriteLine("display types ...");
        Assembly assembly = Assembly.LoadFrom(file);
        foreach (Type type in assembly.GetTypes())
            Console.WriteLine("type name: " + type.FullName);
    }

    // 顯示指定型別所有方法
    public void DisplayMethods() {
        Console.WriteLine("display methods in TestReflection Type ...");
        Assembly assembly = Assembly.LoadFrom(file);
        Type type = assembly.GetType("TestReflection");
        foreach (MethodInfo method in type.GetMethods())
            Console.WriteLine("method name: " + method.Name);
    }

    // 調用靜態方法
    public void InvokeStaticMethod() {
        Console.WriteLine("Invoke static method ...");
        Assembly assembly = Assembly.LoadFrom(file);
        Type type = assembly.GetType("TestSubClass");
        type.InvokeMember("SayHello", BindingFlags.InvokeMethod, null, null, new object[] { });
    }

    // 調用實例方法
    public void InvokeMethod() {
        Console.WriteLine("Invoke Method ...");
        Assembly assembly = Assembly.LoadFrom(file);
        Type type = assembly.GetType("TestSubClass");
        object obj = Activator.CreateInstance(type);
        TestClass tc = (TestClass)obj;
        type.InvokeMember("Test1", BindingFlags.InvokeMethod, null, tc, new object[] { });
        type.InvokeMember("Test2", BindingFlags.InvokeMethod, null, tc, new object[] { });
    }
}

public interface TestClass {
    void Test1();
    void Test2();
}

public class TestSubClass : TestClass {
    public void Test1() { Console.WriteLine("This is TestSubClass.Test1"); }
    public void Test2() { Console.WriteLine("This is TestSubClass.Test2"); }
    public static void SayHello() { Console.WriteLine("This is TestSubClass.SayHello"); }
}

執行輸出

display modules ...
module name: TestReflection.exe
display types ...
type name: TestReflection
type name: TestClass
type name: TestSubClass
display methods in TestReflection Type ...
method name: GetHashCode
method name: Equals
method name: ToString
method name: DisplayModules
method name: DisplayTypes
method name: DisplayMethods
method name: InvokeStaticMethod
method name: InvokeMethod
method name: Test2
method name: GetType
Invoke static method ...
This is TestSubClass.SayHello
Invoke Method ...
This is TestSubClass.Test1
This is TestSubClass.Test2

關鍵 API 解析

Assembly.LoadFrom vs Load

Type.GetMethods 回傳順序

包含繼承自 Object 的方法（GetHashCode、Equals、ToString、GetType），順序不保證，勿依賴順序邏輯。

InvokeMember 綁定旗標

// 靜態方法
type.InvokeMember("SayHello", BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static, null, null, args);

// 實例方法
type.InvokeMember("Test1", BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance, null, instance, args);

// 非公開成員
BindingFlags.NonPublic | BindingFlags.Instance

// 忽略大小寫
BindingFlags.IgnoreCase

Activator.CreateInstance 多載

// 無參數建構子
object obj = Activator.CreateInstance(type);

// 有參數建構子
object obj = Activator.CreateInstance(type, arg1, arg2);

// 指定建構子綁定旗標
object obj = Activator.CreateInstance(type, BindingFlags.NonPublic | BindingFlags.Instance, null, args, null);

效能考量與最佳化

委派快取模式

private static readonly Dictionary> _methodCache = new();

public object InvokeCached(object target, string methodName, params object[] args) {
    var key = $"{target.GetType().FullName}.{methodName}";
    if (!_methodCache.TryGetValue(key, out var func)) {
        var method = target.GetType().GetMethod(methodName);
        func = (instance, parameters) => method.Invoke(instance, parameters);
        _methodCache[key] = func;
    }
    return func(target, args);
}

安全性與權限

• 反射需 ReflectionPermission（全信任環境預設滿足）
• 存取非公開成員需 ReflectionPermissionFlag.MemberAccess
• 部分信任環境（ClickOnce、Silverlight）受限
• .NET Core / .NET 5+ 精簡反射 API，部分功能需 System.Reflection.Metadata

總結

反射是 C# 動態能力的核心，支援外掛、框架、工具開發。關鍵在於平衡靈活性與效能：熱路徑使用委派快取或原始碼生成，冷路徑直用 MethodInfo.Invoke。掌握 BindingFlags 組合、建構子選擇、泛型方法構造（MakeGenericMethod）是進階反射必備技能。