TList and TDictionary descendant

[Alberto Zen]

Good afternoon

I did same trials with TList and TDictionary descendants, If i create the instances for the objects using Create constructor everything works fine, But if i try to register the two types into GlobalContainer and then to obtain the instances via GetService function, the instances of the objects don’t work. If i try to add some item to the collections i receive an exception and the same when i close the application, when the destructor of the descendants are called.

I tried to put some breakpoints on the Create constructor code but i can’t see the program execution passing the breakpoints. The objects was instantiated into the correct type but it’s like the creation process doesn’t work fine. I attach a project to explain better the beaviour i met.

Best regards

[Stefan Glienke]

The behavior you observe might very well be true because the parameterless ctor is not the one to be called to have a fully operational instance of some of the collection types hence the methods from TCollections - collections should always be created via them - all the implementing classes are implementation details that are also always subject to change - as happening in 2.0.

I also advice against treating collection types as injectables but create them yourself using the aforementioned methods from TCollections. There is a chapter about the difference between creatables and injectables in Nicks book and also in this blog post: https://medium.com/better-programming/five-principles-of-dependency-injection-5bd0cca9cb04

P.S.: FWIW due to the changes on the implementing classes ctors that are not virtual anymore in 2.0 the example code provided works with a slight change and that is calling inherited Create(0, nil, nil,[]); in TMyInterfaceDictionary.Create.