Invokers

Invokers: Dependency Resolution At Invocation

The Infusion IoC system provides a mechanism for creating public component functions whose arguments are resolved from the environment at invocation time. This differs from subcomponent, whose dependencies are resolved a single time, at creation. With invokers, the dependencies are "re"-resolved each time the function is invoked.

Declaring Invokers

Defaults

Invokers can declared similarly to subcomponents: Using a default/option called invokers:


fluid.defaults("component.name", {
    invokers: {
        invokerName1: {
            funcName: "name.of.implementation.function1",
            args: [...]
        },
        invokerName2: {
            funcName: "name.of.implementation.function2",
            args: [...]
        }
        ...
    }
});

When dependencies are initialized using fluid.initDependents, the invoker names (invokerName1 and invokerName2 in this example) will be used to create functions that will be attached to the component that object. The functions will resolve the values specified in the arguments and pass them to the function named by funcName.

Demands for Invokers

As with subcomponents, demands can be registered for invokers using fluid.demands. In this case, the declaration in the defaults is slightly different:


fluid.defaults("component.name", {
    invokers: {
        invokerName1: "demandingName"
        ...
    }
});
fluid.demands("demandingName", "component.name", {
    funcName: "name.of.implementation.function1",
    args: [...]
});

The form of the demands specification is the same for invokers as for subcomponents.

No arguments

If the implementing function requires no arguments, it can be declared directly in the defaults:


fluid.defaults("component.name", {
    invokers: {
        invokerName1: "implementing.function"
    }
});

This is essentially shorthand for:


fluid.defaults("component.name", {
    invokers: {
        invokerName1: {
            funcName: "implementing.function"
        }
    }
});

Argument to Invokers

The arguments list specified in an invoker declaration can include:

references to the parent component, which will be resolved at invocation time;
references to the parameters to the invoker, in the format "@i" where i is the index of the parameter.

Examples of Arguments to Invokers

Examples

The following two methods of declaring an invoker are equivalent: