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‫Hello and welcome.

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‫In this lecture, we are going to be setting up the link between the mover and the trigger using a technique

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‫called dependency injection so that by the end of the lecture, if we stick the gargoyle in, then the

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‫door moves down, or at least partially does.

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‫Let's dive in and see how this works.

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‫And I grab a cup.

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‫We've seen that there is a dependency, what we call a dependency for the physics handle.

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‫This grabber cannot do its work unless you have a physics handle component somewhere around now it just

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‫so happens that the trigger component is the same.

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‫The trigger component, in order to do its work properly, needs to have access to a mover component.

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‫However, it's a little bit trickier in this case because sure, in the case of our secret door, the

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‫trigger and the moving object are within the same actor.

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‫So you could get an object by finding the a component of type on the actor.

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‫But what if and we will have this situation in my script where I want my trigger to be on a different

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‫part of the room from the actor that is moving well to allow for that kind of flexibility.

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‫We want it such that the trigger doesn't have to go and find its own dependencies.

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‫And there's actually a name for this kind of program concept.

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‫It's called dependency injection.

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‫Basically, it's in the case where we've got something that says, I need another object, but I can't

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‫find it myself or I don't want to find it myself.

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‫And it's often sensible to not leave it up to the object that's doing its own job, making it have another

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‫job of trying to get hold of an object.

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‫So the way we can do this is to create a mechanism for blueprints to tell the trigger component where

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‫to find a mover.

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‫And the way we're going to do this is by creating a blueprint callable function on our trigger component.

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‫So it's going to be public.

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‫We're going to put it in the public section underneath the tick component, and it's going to be a U

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‫function so that it can be then in the parentheses, blueprint callable.

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‫And there doesn't need to be much to this function.

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‫It's going to be void because it don't need it to return a thing, but it's going to be set mover so

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‫it's going to set a link to the mover and in order for it to set a link to the mover, it needs to take

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‫in a pointer to a mover component.

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‫So that's going to be you mover star and we can just call this the mover like so and put semicolon at

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‫the end of that line.

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‫And we need to store this somewhere.

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‫So we're going to create a new private variable.

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‫It's not going to be a new property and it's just going to be a U move pointer, which we're going to

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‫call a mover as well.

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‫Like so and what we're going to do is implement this set mover over in the CPP so that it sets this

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‫move a pointer, which by default is going to be null.

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‫And we do have to do one more thing.

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‫We have to include the header file for our mover.

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‫Now in this case, because the header file is in the same folder as the trigger component, all we have

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‫to do is hash include quote mover H and that's going to make sure that the trigger component is aware

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‫of the mover type.

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‫So let's go over into our trigger component.

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‫CP And I'm going to put this below our tick component that we're going to implement set mover.

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‫We're going to put the class you trigger component before and indent it.

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‫Remove the semicolon and add braces.

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‫And essentially all we're going to have to do here, let's change the name just in the C++ file.

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‫It doesn't actually matter whether the name of the parameters matches between header and C++.

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‫So we can change it here and say that the new mover is what's coming in to set mover.

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‫And so we can set our local variable, our class variable mover equal to the new mover like.

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‫So now it's actually pretty important that you don't skip this renaming step because if the input parameter

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‫is the same name as one of the variables on the class, then unreal by default will set that to be an

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‫error.

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‫It's called shadowing and Unreal doesn't want you to do it, so you do need to make sure you have your

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‫parameter name differently to the variable now because these new functions don't always show up with

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‫live coding changes.

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‫I'm going to close down the editor recompile from Visual Studio code and then relaunch from the new

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‫project.

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‫Now let's go to the content drawer, open up our secret wall blueprint and then from our Begin Play

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‫node in the event graph, let's pull off of here and search for set mover.

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‫Now notice there are two options here.

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‫One, it would be to set the component which is also called mover, and one is a function on the trigger

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‫component.

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‫So we want to select the one that's a function on the trigger component.

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‫And then what we want to do is drag in our mover component as the other arguments to this function and

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‫that should do the trick.

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‫It's set the mover at begin play.

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‫So now essentially what we want to happen is that our trigger component should be setting and setting

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‫the should move boolean in here.

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‫So that's going to be my challenge to you to create some public functions in mover and mover.

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‫CP It should be set, should move and it should update that you property variable.

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‫In fact, you can make it not a new property anymore because we're going to be setting it through code

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‫now and then you can put it in the public section.

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‫It needs to be public because we're going to try and access it from our trigger component.

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‫And you can call it on the mover pointer that we've got in the trigger component from its tick component

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‫setting, the appropriate boolean, whether we want it to unlock or lock again, pause the video and

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‫have a go.

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‫Okay welcome back.

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‫So I'm going to remove the property from should move I'm going to go to the public section just under

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‫TTIC component and I'm going to create a void set should move taking in a boolean which we're going

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‫to call should move like so.

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‫And then we're going to take this and go over to the move CP and implement it, replacing the semicolon,

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‫adding in the you move colon, colon class and then basically again we can call this the new should

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‫move and we can say that should move equals new should move.

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‫Now you might be wondering, why don't we just make the variables themselves publicly accessible so

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‫that we can set those directly?

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‫That's generally not good practice in C++ because if you let somebody change your variables, you never

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‫know what could be happening to them.

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‫Whereas if you have a method there to do it for you, it allows you later on to change how you structure

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‫internal variables without having to change your public functions, which means there's fewer updates

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‫to different classes that you have to do.

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‫So generally, as a rule, we always use setters and getters if we need to access variables in other

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‫classes.

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‫So now that we've created that new function, let's go over into trig component CP where we've currently

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‫got our log messages.

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‫What we want to do is access our mover pointer, so we're going to do mover arrow set should move.

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‫And in the case where we've got an acceptable actor, that should be true.

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‫We should move semicolon at the end of the line.

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‫And in the else case, well then we probably shouldn't.

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‫So we're going to do move the arrow set should move and in parentheses put false remove that extra R

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‫that I had on the end of my method and let's recompile now in this case because I've only added this

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‫function in C++ land and it's not blueprint callable.

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‫I don't think I need to actually restart the editor for this functionality to work, close down our

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‫output log, go towards our gargoyle and start playing and pick him up.

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‫Let's go out of this cage and stick it in the alcove and they go, It's moving down, but it stops as

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‫soon as the gargoyle falls out, which is not ideal because the gargoyle is not really held in place

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‫and the wall isn't fully down.

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‫And because it's simulating physics, it's going to get popped out of that alcove, isn't it?

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‫So what we need to do is make sure once we drop it into our trigger area, it gets fixed in there and

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‫just stays.

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‫So that's going to be the subject of the next lecture.

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‫I'll see you there.