C reflection practice

Preface

majority Program Both Handle data , Include read 、 Write 、 operation and Show data .（ graphics It's also A kind of data Of form .） However , about some Program Come on , they operation Of data No Numbers 、 Text or graphics , It is Program and Program type In itself Of Information . of Program And its type Of data go by the name of element data （ metadata）, they preservation stay Program Of Program focus . Program stay Runtime , Sure see other Program Set or Its In itself Of element data . One function Of Program see In itself Of element data or other Program Of element data Of Behavior be called Reflection （ reflection）.

Reflection practice

One . Make assembly

open vs Create a new class library

Click next to configure the path and name of the class library

After creation, add the following code , One created in the code Example class , Add some fields 、 attribute 、 And methods , And marked him with custom features MyAttribute, For future testing

using System;

namespace MyDll
{
    
    // Specify that custom attributes can only be attached to classes 
    [AttributeUsage(AttributeTargets.Class)]
    public sealed class MyAttributeAttribute : System.Attribute
    {
    
        public string Description;
        public string Version;
        public string ReviewId;
        public MyAttributeAttribute(string desc, string ver)
        {
    
            Description = desc;
            Version = ver;
        }
    }
	
    [MyAttribute("MyClass", "1.0", ReviewId = "58946")]
    public class Example
    {
    
        public int a = 567;
        private int b = 555;
        public int B
        {
    
            get
            {
    
                return b;
            }
            set
            {
    
                b = value;
            }
        }
        public void HelloDll()
        {
    
            Console.WriteLine("HelloDll");
        }
        public void PrintOut(string s)
        {
    
            Console.WriteLine(s);
        }
    }
}

After adding the code Using shortcut keys ctr + b Generate MyDll.dll file , At this point, we can in the project MyDll\bin\Debug\netcoreapp3.1 Found under folder MyDll.dll file , Indicates that the generation was successful

Two . test

newly build C# Console Application , Run the test code as follows

// Load assembly 
Assembly assembly = Assembly.LoadFrom(@"D:\STu\csharp_-study\CSharp_Study\MyDll\bin\Debug\netcoreapp3.1\MyDll.dll");
Type type = assembly.GetType("MyDll.Example");
// Create type real columns 
object obj = Activator.CreateInstance(type);
// Calling method 
type.GetMethod("HelloDll").Invoke(obj,null);
// Call a method with parameters 
type.GetMethod("PrintOut").Invoke(obj, new object[] {
     "DLLTEST" });
// get attribute 
PropertyInfo propertyInfo = type.GetProperty("B");
// Set field value 
propertyInfo.SetValue(obj,444);
Console.WriteLine(propertyInfo.GetValue(obj, null));
// Get field 
FieldInfo fieldInfo = type.GetField("a");
// Set field value 
fieldInfo.SetValue(obj, 123);
Console.WriteLine(fieldInfo.GetValue(obj));

Console.WriteLine("================ Get all features ====================");
object[] typeAttributes = type.GetCustomAttributes(false);       // obtain Example Class 
foreach (object attribute in typeAttributes)
{
    
   Console.WriteLine("Attributes description is " + attribute.ToString());
   // Access to features Description Information 
   Console.WriteLine($"Description:{
      attribute.GetType().GetField("Description").GetValue(attribute)}");
}

// Get all members 
Console.WriteLine("================ Get all members ====================");
MemberInfo[] memberInfos = type.GetMembers();
foreach(var item in memberInfos)
{
    
   Console.WriteLine(item.Name);
}
// Get all fields （ Default public , You can set BindingFlags）
Console.WriteLine("================ Get all fields ====================");
FieldInfo[] fieldInfos = type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static);
foreach (var item in fieldInfos)
{
    
   Console.WriteLine(item.Name);
}
// Get all properties 
Console.WriteLine("================ Get all properties ====================");
PropertyInfo[] properties = type.GetProperties();
foreach(var item in properties)
{
    
   Console.WriteLine(item.Name);
}

The output is as follows

matters needing attention

Relationship with Assembly.LoadFrom Methods can be found in MSDN

About Type class ：

1） about Program in be used Of every last type , CLR Metropolis establish One contain This type Information Of Type type Of object .
2） Program in be used Of every last type Metropolis relation To Independent Of Type class Of object .
3） No matter establish Of type Yes How many? individual example , Only One Type object Meeting relation To All of these example .

Abstract

Daniel M·Solis. C# Illustrated tutorial （ The first 4 edition ）（ Turing books ） (p. 481). People's post and Telecommunications Press . Kindle edition .