如何限制添加到派生類的項目類型？

Question

我有繼承自BaseClass的DerivedClass。我想利用重寫InsertItem方法的BaseCollection類，因此我定義了DerivedCollection並從BaseCollection繼承。問題是，DerivedCollection允許添加DerivedClass和BaseClass類型。我只想允許將DerivedClass類型添加到DerivedCollection中。我錯過了什麼？

public class BaseClass 
{ 
    public static string MyString; 
} 

public class BaseCollection<T> : Collection<BaseClass> where T : BaseClass 
{ 
    protected override void InsertItem(int index, BaseClass item) 
    { 
     throw new UnauthorizedAccessException("I'm sorry Dave, I'm afraid I can't do that."); 
    } 
} 

public class DerivedClass : BaseClass 
{ 
    public static int MyInteger; 
} 

public class DerivedCollection : BaseCollection<DerivedClass> 
{ 
} 

Answer 1

繼承
1. 更改BaseCollection<T>繼承自Collection<T>，而不是從Collection<BaseClass>繼承。
2. 適當地更改參數InsertItem。

public class BaseCollection<T> : Collection<T> where T : BaseClass 
{ 
    protected override void InsertItem (int index, T item) 
    { 
     throw new UnauthorizedAccessException("I'm sorry Dave, I'm afraid I can't do that."); 
    } 
} 

Answer 2

你需要重寫InsertItem像這樣：

public class DerivedCollection : BaseCollection<DerivedClass> 
{ 
protected override void InsertItem(int index, DerivedClass item) 
    { 
     base.InsertItem(index, item); 
    } 
} 

Answer 3

你只想讓T：

protected override void InsertItem(int index, T item) 
{ 
    throw new UnauthorizedAccessException("I'm sorry Dave, I'm afraid I can't do that."); 
} 

您也可以從Collection<T>而不是Collection<BaseClass>