I need method that can find component implements interface T. I have this method but i does not work correctly. It should work like TryGetComponent(out Interface interface). Can you help?

public T RaycastFindComponent<T>(T targetType) where T : Type
{
    RaycastHit2D[] raycastHits = Physics2D.RaycastAll(_mainCamera.ScreenToWorldPoint(Input.mousePosition), new Vector2());
    foreach (RaycastHit2D raycastHit in raycastHits)
    {
        foreach (MonoBehaviour component in raycastHit.transform.GetComponents(typeof(MonoBehaviour)))
        {
            Type componentType = component.GetType();
            Debug.Log($"GetComponent = {componentType is T}"); //true
            if (componentType is T)
            {
                return component as T; //null but (componentType is T = true)
            }
        }
    }
    return null;
}

It works if I use concrete Interface:

public Interface RaycastFindComponent()
{
    RaycastHit2D[] raycastHits = Physics2D.RaycastAll(_mainCamera.ScreenToWorldPoint(Input.mousePosition), new Vector2());
    foreach (RaycastHit2D raycastHit in raycastHits)
    {
        foreach (MonoBehaviour component in raycastHit.transform.GetComponents(typeof(Interface)))
        {
            Type componentType = component.GetType();
            Debug.Log($"GetComponent = {componentType is Interface}"); //true
            if (componentType is T)
            {
                return component as Interface; //(Interface)component
            }
        }
    }
    return null;
}

CodePudding user response：

The problem with your code is that you are trying to return a class of type T however the T constraint is defined as Type:

public T RaycastFindComponent<T>(T targetType) where T : Type

...is equivalent to:

public Type RaycastFindComponent(Type targetType) 

...which isn't what you want.

It should read (note we don't need the parameter anymore):

public T RaycastFindComponent<T>() where T : Component, IMyInterface // NEW
{
    var targetType = typeof(T); // <--- NEW

    RaycastHit2D[] raycastHits = Physics2D.RaycastAll(_mainCamera.ScreenToWorldPoint(Input.mousePosition), new Vector2());
    foreach (RaycastHit2D raycastHit in raycastHits)
    {
        foreach (MonoBehaviour component in raycastHit.transform.GetComponents(targetType))
        {
            if (component is T)
            {
                return component as T; 
            }
        }
    }
    return null;
}

You were essentially trying to cast Type to say IMyInterface which is apples and oranges and thus fails.

CodePudding user response：

It should work like TryGetComponent(out Interface interface)

So first of all you want to pass in the type into the generic, not additionally an instance of it as a parameter!

Then secondly in order to really make it work like TryGetComponent

• You want to use an out parameter and return bool
• Why not actually use TryGetComponent which does support interfaces

so something like e.g.

public bool RaycastFindComponent<T>(out T result) where T : class
{
    var raycastHits = Physics2D.RaycastAll(_mainCamera.ScreenToWorldPoint(Input.mousePosition), new Vector2());

    foreach (RaycastHit2D raycastHit in raycastHits)
    {
        if (raycastHit.transform.TryGetComponent<T>(out result))
        {
            return true;
        }
    }

    result = default;
    return false;
}

The constraint class also includes interfaces since they are also reference-type so this can (just like Unity's GetComponent / TryGetComponent) take any class or interface as the generic type parameter.

if(RaycastFindComponent<ISomeInterface>(out var instance))
{
    Debug.Log("You hit {instance}", instance);
}

of course you could constrain it further down if needed, but I would start with the most generic and re-usable way and then you can still make more constrained versions of it