几十行代码实现ASP.NET Core自动依赖注入

于是就会经常进行一个很频繁的的重复动作：定义一个接口->写实现类->注入

有时候会忘了写Add这一步，看到屏幕上的报错一脸懵逼，然后瞬间反应过来忘了注入了。赶紧补上serviceCollection.AddXXX这句话

虽然说有很多开源框架已经实现了类似的工作，比如AutoFac，Unity等依赖注入框架。但是这些库都太庞大了，我个人还是喜欢轻量级的实现。

定义一个枚举

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class AutoInjectAttribute : Attribute
{
public AutoInjectAttribute(Type interfaceType, InjectType injectType)
{
Type = interfaceType;
InjectType = injectType;
}

public Type Type { get; set; }

/// <summary>
/// 注入类型
/// </summary>
public InjectType InjectType { get; set; }
}

定义三种注入类型

/// <summary>
/// 注入类型
/// </summary>
public enum InjectType
{
Scope,
Single,
Transient
}

扫描运行目录下所有的dll，进行自动注入

/// <summary>
/// 自动依赖注入
/// </summary>
public static class AutoInject
{
/// <summary>
/// 自动注入所有的程序集有InjectAttribute标签
/// </summary>
/// <param name="serviceCollection"></param>
/// <returns></returns>
public static IServiceCollection AddAutoDi(this IServiceCollection serviceCollection)
{
var path = AppDomain.CurrentDomain.BaseDirectory;
var assemblies = Directory.GetFiles(path, "*.dll").Select(Assembly.LoadFrom).ToList();
foreach (var assembly in assemblies)
{
var types = assembly.GetTypes().Where(a => a.GetCustomAttribute<AutoInjectAttribute>() != null)
.ToList();
if (types.Count <= 0) continue;
foreach (var type in types)
{
var attr = type.GetCustomAttribute<AutoInjectAttribute>();
if (attr?.Type == null) continue;
switch (attr.InjectType)
{
case InjectType.Scope:
serviceCollection.AddScoped(attr.Type, type);
break;
case InjectType.Single:
serviceCollection.AddSingleton(attr.Type, type);
break;
case InjectType.Transient:
serviceCollection.AddTransient(attr.Type, type);
break;
default:
throw new ArgumentOutOfRangeException();
}
}
}

return serviceCollection;
}
}

使用自动依赖注入功能

public void ConfigureServices(IServiceCollection services)
{
services.AddAutoDi();
}

public interface ITest
{
string Say();
}

[AutoInject(typeof(ITest),InjectType.Scope)]
public class Test : ITest
{
public String Say()
{
return "test:"+DateTime.Now.ToString();
}
}

再次运行程序，所有的贴有

AutoInject

青城同学