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Injection and Inheritance [message #671713]

Wed, 18 May 2011 18:58

Christian Eugster

Messages: 203
Registered: July 2009
Location: St. Gallen Switzerland

Senior Member

Hi,
I am playing around with the (for me) new concept of dependency injection. While that works without any problems when I inject into a concrete workbench part in e4, I get an exception (to be precicely a NullPointerException thrown by InjectorImpl.resolveArgs) injecting the same services into the abstract parent class. Because I am new to the concept of injection I would like to know if this is just not possible or if there is a way to do that. Thank you.

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Re: Injection and Inheritance [message #671722 is a reply to message #671713]

Wed, 18 May 2011 19:31

Paul Webster

Messages: 6859
Registered: July 2009
Location: Ottawa

Senior Member

You mean you have:

public abstract class Parent {
@Inject
protected SomethingUseful something;
//...
}

public class Child extends Parent {
// ...
}

// somewhere later:
ContextInjectionFactory.make(Child.class, context);

and you get that error?

Later,
PW

Paul Webster
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Re: Injection and Inheritance [message #671734 is a reply to message #671722]

Wed, 18 May 2011 20:09

Christian Eugster

Messages: 203
Registered: July 2009
Location: St. Gallen Switzerland

Senior Member

I use part A as a view and part B as editor. When the user selects an entry in the viewer in A, the selection is propagated via selectionservice. Editor B inherits from an abstract class c that is a generic type:

public abstract class AbstractEditor<T extends AbstractEntity>
{
}

The concrete editor B:

public class DescriptorTemplateEditor extends AbstractEditor<DescriptorTemplate>
{
}

I want to catch the propagated selection by a concrete method in the abstract class like:

@Inject
public void setModel(@Optional @Named(IServiceConstants.ACTIVE_SELECTION) T model)
{
if (model != null)
{
this.getModel().setModel(model);
this.getPartService().getActivePart().setDirty(false);
}
}

Now the Exception is thrown in InjectorImpl.resolveArgs. ON line 476 in my current version is a parameter of that method evaluated:

Class<?> descriptorsClass = getDesiredClass(descriptors[i].getDesiredType());

where the desiredtype is a T. So the method getDesiredClass returns null.

Good Evening

Christian

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Re: Injection and Inheritance [message #671748 is a reply to message #671734]

Wed, 18 May 2011 21:02

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

Hm, I don't think this can work because of the typ erasure happening in
Java but I could be wrong.

Tom

Am 18.05.11 22:09, schrieb Christian Eugster:
> I use part A as a view and part B as editor. When the user selects an
> entry in the viewer in A, the selection is propagated via
> selectionservice. Editor B inherits from an abstract class c that is a
> generic type:
>
> public abstract class AbstractEditor<T extends AbstractEntity>
> {
> }
>
> The concrete editor B:
>
> public class DescriptorTemplateEditor extends
> AbstractEditor<DescriptorTemplate>
> {
> }
>
> I want to catch the propagated selection by a concrete method in the
> abstract class like:
>
> @Inject
> public void setModel(@Optional
> @Named(IServiceConstants.ACTIVE_SELECTION) T model)
> {
> if (model != null)
> {
> this.getModel().setModel(model);
> this.getPartService().getActivePart().setDirty(false);
> }
> }
>
> Now the Exception is thrown in InjectorImpl.resolveArgs. ON line 476 in
> my current version is a parameter of that method evaluated:
>
> Class<?> descriptorsClass =
> getDesiredClass(descriptors[i].getDesiredType());
>
> where the desiredtype is a T. So the method getDesiredClass returns null.
>
> Good Evening
>
> Christian

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