通過使用泛型避免在下面的代碼中鑄造

Question

我是新來的泛型，只是想知道是否有可能避免使用更好的面向對象方法在下面的代碼中投射。

public class CollectorFactory 
{ 
    public static MyCollector Create(ICredential credential) 
    { 
     return new MyCollector(credential); 
    } 
} 

public class MyCollector { 

    public MyCredential Credential { get; set; } 

    public MyCollector(ICredential credential) 
    { 
     this.Credential = (MyCredential)credential; 
    } 

    public void Show() 
    { 
     Console.WriteLine(this.Credential.Username); 
     Console.WriteLine(this.Credential.AuthToken); 
    } 
} 

public class MyCredential : ICredential 
{ 
    public string Username{ get; set; } 

    public string AuthToken { get; set; } 
} 

public interface ICredential 
{ 

} 

有沒有辦法救ICredential到MyCredential在MyCollector的構造鑄造？我沒有選擇將Username和AuthToken放入ICredential，因爲它由兩個不同的憑證實現，這兩個憑證都具有不同的屬性集。 CollectorFactory將來將返回不同的MyCollector實例，並且都需要具有不同的憑據。

任何幫助將非常感激。

Answer 1

我不認爲這是可能的，因爲你正在實施不同的憑據，並試圖將它們用於ICredential。

Answer 2

泛型不是這種情況下的解決方案。這裏的問題是您的工廠正在返回特定類型（MyCollector）。解決方案如下：

public class CollectorFactory 
{ 
    public static ICollector Create(MyCredential credential) 
    { 
     return new MyCollector(credential); 
    } 
    public static ICollector Create(OtherCredential credential) 
    { 
     return new OtherCollector(credential); 
    } 
} 

public interface ICollector 
{ 
    void Show(); 
} 

public class MyCollector : ICollector 
{ 

    public MyCredential Credential { get; set; } 

    public MyCollector(MyCredential credential) 
    { 
     this.Credential = credential; 
    } 

    public void Show() 
    { 
     Console.WriteLine(this.Credential.Username); 
     Console.WriteLine(this.Credential.AuthToken); 
    } 
} 

public class MyCredential : ICredential 
{ 
    public string Username{ get; set; } 

    public string AuthToken { get; set; } 
} 

public interface ICredential 
{ 

} 

以上幾乎是工廠設計模式的規範示例。

相反，你也別在工廠類型檢查重載：

public class CollectorFactory 
{ 
    public static ICollector Create(ICredential credential) 
    { 
     if(credential.GetType() == typeof(MyCredential)) 
      return new MyCollector((MyCredential) credential); 
     if(credential.GetType() == typeof(OtherCredential)) 
      return new OtherCollector((OtherCredential) credential); 
    } 
} 

Answer 3

這裏是這樣使用泛型的方式。請閱讀我在代碼中的評論。

public class CollectorFactory<T> 
{ 
    public T Create(ICredential credential) 
    { 
     return (T)Activator.CreateInstance(typeof(T), credential); 
    } 
} 

public class MyCollector : BaseCollector 
{ 
    public dynamic Credential { get; private set; } 

    public MyCollector(ICredential credential) 
     : base(credential) 
    { 
     this.Credential = credential; 
    } 

    // Having this method here limits your ability to make it more generic. 
    // Consider moving this to MyCredential since it refers to specific properties in MyCredential. 
    // If that is not what you want, then you must do a type check before calling methods/ accessing props in Credentials. 
    public void Show() 
    { 
     Console.WriteLine(this.Credential.Username); 
     Console.WriteLine(this.Credential.AuthToken); 
    } 
} 

public class MyCredential : ICredential 
{ 
    public string Username { get; set; } 

    public string AuthToken { get; set; } 
} 

public abstract class BaseCollector : ICredentialCollector 
{ 
    protected BaseCollector(ICredential credential) 
    { 
     if (credential == null) 
     { 
      throw new ArgumentNullException(nameof(credential)); 
     } 
    } 
} 

public interface ICredentialCollector 
{ 
} 

public interface ICredential 
{ 
} 

// test implementation 
public class TestClass 
{ 
    public void AuthFactoryTest() 
    { 
     // test auth instance 
     MyCredential auth = new MyCredential() {AuthToken = "asfgasdgdfg", Username = "xuser"}; 

     // Create test factory 
     var fact = new CollectorFactory<MyCollector>(); 
     var myCollector = fact.Create(auth); 

     // Do what you need to do to collector object 
     myCollector.Show(); 
    } 
}