无法使用 Autofac 进行属性注入

Question

我是 autofac 的新手。我正在尝试使用这个 IoC 容器进行属性注入。以下是我的代码。我收到错误：

对象引用未设置为对象的实例

在这一行： . return _salary.employeeSalary;在GetSalary(int employeeId) 方法中。在我什至尝试过的程序类中，build.RegisterType<Employee>().WithProperty("_salary", new Salary{ employeeId = 5, employeeSalary = 500 });

public interface IEmployee
{
    double GetSalary(int employeeId);
}
public interface ISalary
{
    int employeeId { get; set; }
    double employeeSalary { get; set; }
}
public class Salary : ISalary
{
    public int employeeId {get; set;}
    public double employeeSalary { get; set; }
}

public class Employee: IEmployee
{
    public ISalary _salary;        

    public double GetSalary(int employeeId)
    {
        if (employeeId == 5)
        {
            return _salary.employeeSalary;
        }
        else
        {
            return 0;
        }
    }
}

public class Program
 {
     static void Main(string[] args)
     {
         var build = new ContainerBuilder();
         build.RegisterType<Salary>().As<ISalary>();
         build.RegisterType<Salary>().As<ISalary>().PropertiesAutowired();               
         var container = build.Build();
         Employee employee = container.Resolve<Employee>();

         Console.WriteLine(employee.GetSalary(5));
         Console.ReadLine();            
     }
}

Answer 1

选项 1：

为了让Property Injection 使用属性，请注意_salary 是一个字段，您需要将它配置为一个属性 .

除了@ehasanul-hoque answer，您还可以将_salary 字段修改为私有并添加一个公共属性，例如（有关详细信息，请参阅此answer）：

private ISalary _salary;

public ISalary Salary
{
    get
    {
        return this._salary;
    }
    set
    {
        _salary = this.value;
    }
}

选项 2：

如果您仍然不想将其转换为属性，您可以使用Method Injection，通过添加SetSalary 方法，例如：

public class Employee: IEmployee
{
    private ISalary _salary;

    public void SetSalary(ISalary salary)
    {
        this._salary = salary;
    }
}

构建器可能看起来像：

var builder = new ContainerBuilder();
builder.RegisterType<Salary>().As<ISalary>();
builder.RegisterType<Employee>()
    .OnActivated(IActivatedEventArgs<Employee> e) =>
    {
        var salary = e.Context.Resolve<ISalary>();
        e.Instance.SetSalary(salary);
    });

var container = build.Build();
Employee employee = container.Resolve<Employee>();

Answer 2

你需要像下面这样定义你的属性

public ISalary _salary { get; set; }

那么下面的代码将为你工作

var build = new ContainerBuilder();
// build.RegisterType<Salary>().As<ISalary>();
build.RegisterType<Salary>().As<ISalary>();
build.RegisterType<Employee>().As<IEmployee>().PropertiesAutowired();
var container = build.Build();
IEmployee employee = container.Resolve<IEmployee>();

Console.WriteLine(employee.GetSalary(5));
Console.ReadLine();

Answer 3

在Employee中创建构造函数

    public Employee(ISalary salary)
    {
        _salary = salary;
    }

这样注册员工

build.RegisterType<Employee>().As<IEmployee>()
            .WithParameter(new TypedParameter(typeof(ISalary), "salary"));

这样解决

var employee = container.Resolve<IEmployee>(new NamedParameter("salary",
                new Salary { employeeId = 5, employeeSalary = 500 }));