C foundation 8-reflection and dependency injection

Reflection

Reflection can occur when the loader is running , Get and load assemblies dynamically , And you can get the information of the assembly

Reflection is to get classes dynamically at run time 、 object 、 Method 、 Object data is an important means

Mainly used class libraries ：System.Reflection

Core class ：

1. Assembly Describes the assembly
2. Type Describes the type of class
3. ConstructorInfo Describes the constructor
4. MethodInfo Describes all the methods
5. FieldInfo Describes the fields of the class
6. PropertyInfo Describes the properties of the class

Through the above core classes, you can dynamically obtain the classes in the assembly at run time , And execute class construction to generate class objects , Get the field or property value of the object dynamically , It can also dynamically execute class methods and instance methods .

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Here is B standing c sharp Teacher Liu tiemn The first phase Dependency injection 、 Reflection in relevant chapters , An example of a toy program that simulates the sound of small animals .

The developer announced SDK ( dll ) 、 One store MOD file ( dll ) The catalog of And toy program

Other developers quote SDK , The small animals developed by ourselves (dll) Put in storage MOD In the directory of the file , Run the toy program provided by the developer , This expands the content of the toy program

---

SDK

The developer announced a SDK To other developers , Including a feature and a small animal interface

namespace sdk;
public class UnfinishedAttribute : Attribute
{
    

}

If other developers write code for small animals to make noises , Not yet completed , Add this attribute to the class
Just like this.

namespace Animals1;
using sdk;
[Unfinished]
public class Bird : IAnimal
{
    

    public void Voice(int times)
    {
    
        for (int i = 0; i < times; i++)
        {
    
            System.Console.WriteLine(" Serge ");
        }

    }
}

The purpose of using the interface is to restrict the small animal classes written by developers , There must be a way to make a sound Voice

namespace sdk;
public interface IAnimal
{
    
    void Voice(int times);
}

Then developers publish their sdk.dll

Use SDK

As a developer , Use CLI Create a command line program Name it Animals1, We should quote the developers' share in the project DLL Reference through assembly
Notice the file path ..\sdk.dll
modify Animal1.csproj Project profile , Add reference

...
  <ItemGroup>
    <Reference Include="sdk">
      <HintPath>..\sdk.dll</HintPath>
    </Reference>
  </ItemGroup>
...

Write a calf

namespace Animals1;
using sdk;
// [Unfinished]
public class Cow : IAnimal
{
    
    public void Voice(int times)
    {
    
        for (int i = 0; i < times; i++)
        {
    
            System.Console.WriteLine(" Moo ");
        }

    }
}

Construction Engineering , Generated Animals1.dll Assembly of
Suppose that the developer requires MOD Files in Animals Under the table of contents , Then put Animals1.dll Copy to the directory

Toy program

In the toy program that simulates animal calls , There is a small animal list , The user enters the corresponding number on the command line , Call... In the linked list The first n A little animal , Make a cry m Time

This requires dynamic loading Animals All under directory DLL file , Judge whether the class inside implements IAnimal Interface , Make sure there is a way to make a sound , And judge the characteristics of the class , There is no sign of UnfinishedAttribute features , Just add the small animals inside to the linked list .

Introducing class library , Developers can directly introduce SDK engineering

//  introduce  assembly.GetTypes
using System.Reflection;
//  introduce  AssemblyLoadContext
using System.Runtime.Loader;
using sdk;

Define the small animal list

var folder = Path.Combine(Environment.CurrentDirectory, "Animals");
var files = Directory.GetFiles(folder);
var animalsTypes = new List<Type>();

Dynamic loading DLL , Add the small animals released by the developer to the small animal list

foreach (var file in files)
{
    
    //  Load assembly 
    var assembly = AssemblyLoadContext.Default.LoadFromAssemblyPath(file);
    //  Get reflection 
    var types = assembly.GetTypes();
    foreach (var t in types)
    {
    
        //  As long as there's a way   Just add 
        // if (t.GetMethod("Voice") != null)
        // {
    
        // animalsTypes.Add(t);
        // }
        //  Use  SDK  If there are settings   Hang in the air   characteristic , Do not add 
        if (t.GetInterfaces().Contains(typeof(IAnimal)))
        {
    
            //  Access to features 
            var ifUnfinished = t.GetCustomAttributes(false).Any(a => a.GetType() == typeof(UnfinishedAttribute));
            if (ifUnfinished)
            {
    
                continue;
            }
            animalsTypes.Add(t);
        }
    }
}

Processing user input

while (true)
{
    
    try
    {
    
        for (int i = 0; i < animalsTypes.Count; i++)
        {
    
            System.Console.WriteLine($"{
      i + 1},{
      animalsTypes[i].Name}");
        }
        System.Console.WriteLine("==================\nchoice animal 1~ ? hit 0 to break;");
        int index = int.Parse(Console.ReadLine());
        if (index == 0)
        {
    
            break;
        }
        if (index > animalsTypes.Count || index < 1)
        {
    
            System.Console.WriteLine("error index");
            continue;
        }
        System.Console.WriteLine("How many times ?\nhit 0 to break;");
        int times = int.Parse(Console.ReadLine());
        if (times == 0)
        {
    
            break;
        }

        var t = animalsTypes[index - 1];
        var m = t.GetMethod("Voice");
        var o = Activator.CreateInstance(t);
        //  change to the use of sth.  SDK 
        // m.Invoke(o, new object[] { times });
        var a = o as IAnimal;
        a.Voice(times);
    }
    catch (System.Exception)
    {
    
        throw;
    }
}

Print the results

Input in sequence
2 enter
3 enter
exit enter
notice 2 The little dog barked 3 Time , The code of kitten and puppy is the same as that of calf , It can be constructed separately Animal2.dll Put in Animals Under the table of contents

1,Cat
2,Dog
3,Cow
==================
choice animal 1~ ? hit 0 to break;
2
How many times ?
hit 0 to break;
3
 Wang 
 Wang 
 Wang 
1,Cat
2,Dog
3,Cow
==================
choice animal 1~ ? hit 0 to break;
exit
Unhandled exception. System.FormatException: Input string was not in a correct format.
   at System.Number.ThrowOverflowOrFormatException(ParsingStatus status, TypeCode type)
   at System.Int32.Parse(String s)

c# How the program references external DLL

Internal library ( Libraries of other projects under the same solution ), Just use the command line tool directly add reference Quote other projects

External libraries , Need to use csc Command line tools , Link the library and compile

csc /out:xxxxx.exe /reference:xxx.dll xxxxx.cs

Another way is to modify the project file directly json After profile , Re execution dotnet restore Automatically download the modified dependencies

{
  "dependencies": { //nuget Dependency package 
    "EntityFramework": "6.1.3",
    "Microsoft.AspNet.StaticFiles": "1.0.0-rc1-final",
    "Microsoft.Dnx.Runtime": "1.0.0-rc1-final",
    "Microsoft.Extensions.Configuration": "1.0.0-rc1-final",
    "Microsoft.Extensions.Configuration.Json": "1.0.0-rc1-final",
    "PimProject.Common": "1.0.0"
  },
  "frameworks": {
    "dnx451": {
      "dependencies": {
      },
      "frameworkAssemblies": { // Reference is made here to external dll file 
        "System.Data": "4.0.0.0"
      }
    }
  },
  "dotnet": {
    "dependencies": {
      "System.Data.SqlClient": "4.0.0-rc2-23530",
        "System.Data":  "4.0.0"
    }
  },
   "version": "1.0.0-*",
  "description": "Class Library",
  "authors": [ "sadams" ],
  "tags": [ "" ],
  "projectUrl": "",
  "licenseUrl": ""
}

Another method is the one mentioned earlier in this article “ Use SDK” It's about , Manually edit the project configuration file of the project