Callbacks.md

2020-09-30_13:13:51

Callbacks

TFunction<> is a lower level primitive that is able to bind anything, including UObject function members. It's similar to std::function<>.

There are also delegates, both single and multi.

FMenuBuilder::AddMenuEntry uses FUIAction for its callbacks. The FUIAction can be created from FExecuteAction::CreateLambda(), which in turn is created from a C++ lambda. FExecuteAction is a TBaseDelegate_NoParams.

Slate

In Slate we can use both lambdas and function pointers. In the below a combo box is created but I assume the process is the same in most cases.

vid UMyClass::MyFunction()
{
    SNew(SComboBox<TSharedPtr<FName>>)
    // The callbacks that add a lambda all have _Lambda at the end of their
    // name. I guess this is because the lambda version is templated and they
    // don't have a way to disable the overload for non-lambda types.
    .OnGenerateWidget_Lambda([](TSharedPtr<FName> Item))
    {
        return SNew(STextBlock)
            .Text(FText::FromName(*Item))
    })
    // Member function callbacks are registered by passing in a pointer to the
    // object which should receive the call, a function pointer to the member
    // function that should be called, and an optional list of extra parameters.
    // The extra parameters are passed on to the member function but otherwise
    // ignored by the callback framework.
    // The signature of the member function must match the type of the callback.
    // That is, it must take all the parameters that the callback source always
    // passes, and the rest of the parameters should match the extra parameters
    // that we list here.
    .OnSelectionChanged(
        this, &FMyClassCustomization::MyCallback, ExtraParameter)
}

[[2020-08-22_13:21:00]] RF_Transactional
[[2021-03-10_10:35:35]] Timer
[[2020-06-29_13:29:35]] Events
[[2021-03-10_10:42:34]] Delegate

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