从表象基类继承的类实例创建新的类实例/重置类实例

Question

Prior I'd like to appologize for the long title but I didn't figure out a shorter version.

I have an abstract base class that delivers generic methods to access functions in test classes, that derive from my base class.

I have a collection of classes that itself have a reference to those test classes.

The struct is:

// A really simplified example for my manager
Collection<AbstractBaseClass> Manager = new Collection<AbstractBaseClass> 
{
    TestClassA();
    TestClassB();
}

Now I come to the point that I need to kill and recreate the instance in the collection of the testclass without knowledge of which testclass is in this collection.

I try to do sth. like (pseudocode)

Manager[0] = null;
Manager[0] = new (object)Manager[0].GetType();

I already stumbled over Get a new object instance from a Type but this - however - doesn't work because CreateInstance is no member of System.Activator . Also I cannot find the ObjectType class.

Long explaination, short question: How can I create a new instance from a class where I only have an Instance?

Thank you very much, ADP.

Answer 1

如果您知道所有类都有一个公共的无参数构造函数，则可以执行以下操作：

manager[i] = (AbstractBaseClass)Activator.CreateInstance(manager[i].GetType());

Answer 2

While you could use Activator.CreateInstance to create instances from a given type, maybe you can solve this in a more optimal way using generics :

public sealed class TestCollection<T> : ICollection<T>
   where T : AbstractBaseClass, new()
{
    private List<T> Tests { get; } = new List<T>();

    public T this[int index] => Tests[index];

    public void Add(T test) => Tests.Add(test);

    // Rest of ICollection<T> members

    public void NewAt(int testIndex) => Tests[testIndex].Insert(testIndex, new T());
} 

Now you don't need reflection anymore, because T must be a class with a public, paramaterless constructor :

TestCollection<AbstractBaseClass> manager = new TestCollection<AbstractBaseClass>();
manager.Add(new Test());
manager.Add(new Test());
manager.Add(new Test());

manager.NewAt(1);

Now you've already created a new instance of Test without reflection on index 1 and you can still access the new object typed as Test using the TestCollectin<T> indexer: manager[1] .