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So well coming again in this listen we're going to talk about selectors and class types.

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So select essentially a way for us to find out if a certain object can respond to a certain function

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and class type is essentially used to find out the type of the class that has made this current object

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essentially a way to find out which class has instantiated this particular object.

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Now let's go to school and get this done.

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And just so that you know every once in a while we go back to the whole objective see mode.

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I'm going to do both of these in Objective-C this time.

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So in school I'm going to go ahead and say Give me a new command line tool in Objective-C and it's got

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selectors Objective-C

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now in my heart.

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Emma I'm going to go ahead and say I have something called an s mutable array called my array which

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is and is mutable.

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Array new is just a brand new allocator initialized array.

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Then I'm going to go ahead and do this.

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I'm going to say my array perform selector Vitt object and the selector they want to apply to it is

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called that selector that is called add object for instance and the object that when out is perhaps

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mining.

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That's all I want to do in here.

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Now you might be asking yourself Is this a safe way of doing it.

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Are you just assuming that mutable array no matter what can take an object to it.

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And the answer to that is no it actually another very safe way of doing it and much safer way would

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be nice if I said if my array responds to selector and this I want to use is called selector add object

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if that is true then I want to do this whole thing.

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Otherwise I don't mind waiting.

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So that's about that if my error rate response to this selector then do that thing add to it for instance

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a value and that's pretty much all there is to a selector in the past you have seen selectors that I

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as an Baden's For instance I said My.

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Then as the target target was self with selector and the selector was at select store on name of functions

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so on and so forth.

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And that's how we use selectors to make sure that something does respond to a certain function not a

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much bigger question for you might be so.

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I know this is an array and I know it can have an object.

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So what's the point of using this.

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So the answer to that would be in a situation like this when we have an array of objects that we don't

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know what they are.

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So let's go ahead and make that and I'm actually going to make this a slightly more broader application

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so I can use it for class type husband.

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So I'm glad you don't say command and I'm going to make a cocoa class of the type in its object language

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is objective c I'm going to call it car.

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So I have a daughter age and a dot M for a car.

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And I also have at that age that am for a person and I have a last command an adult age an adult am

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for let's say a building.

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So cars buildings and people.

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And we have three classes in here.

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Now I'm going to go do some clean up in all of those.

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So you know things are a lot easier for us to see and to understand that that ends I don't have anything

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into that.

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Again I'm going to remove the nullable again.

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And then the same thing in year is going to be rather simple so don't worry about having too many files

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and everything is going to be much easier.

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So the first thing I want to do is I want to go to the car at that age and say every one of these classes

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says they have a method called the law Kate.

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So that's essentially going to place my objects my cards my people my whatever in some place.

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Also of course they have something called Change gear of not like that.

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Not like that change.

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So they have two methods and get a copy that I'm going to go to my dad and doesn't have to have an actual

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implementation.

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As long as we have the curly brackets so that's that.

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I'm going to go to my person and say well my person does have it ok but cannot change gear but can't

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eat somebody copy these to go to my person that am on say do the same thing have a body for the functions

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so you don't get an error when you go to the building.

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The building they have it.

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And they can not have something that does eat but they can have something called Lights on the lights

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they turn on them and they copy those and go to the top.

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And of course the same thing as always.

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So now I have three classes that the three of them they have a method in them called locate bought each

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of them has one extra metadata and yet on the other one lights on.

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Now I'm going to go to my dad and I'm going to import all three of them and when I say import or whatever

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name port is call and I want to go ahead and say building and I want to go ahead and say person.

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So all three of them are either in here and in my array before I do any of these things I'm going to

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go ahead and make three copies.

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I'm going to say car let's say Jeep is going to be our car.

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You know I have one jeep.

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My copy is twice even though that was a very good idea person myself is person you're building.

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Let's call it of Empire State.

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I don't know a name of any buildings to be honest.

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All the buildings are numbered like the number 226 or whatever.

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So that's about that.

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So I have a car.

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I have a person and I have a building and they're all added to my array just so that they can make things

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easier.

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I'm going to cut them up here paste them in here and say I look on to the objects and the objects are.

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I mean the Empire State Building.

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Perfect.

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So now I have an array with mixed objects so I don't know what they are.

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I don't know.

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You know what do they actually.

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What can they do for now.

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I could go ahead and say for Gints my ears 0 is a smaller than my array that counts.

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And then I press plus do this.

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What am I going to do.

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I'm going to say if my array object that index responds to selector and let's say the selector that

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I want to use it.

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If it does respond to it which is this then it's down and eat.

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So while this example may not really do anything for us it explains to you why we would end up using

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selectors.

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We use it for when we don't know what the object is what is it capable of it might be useful.

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And you know whether they do respond to a certain select or they don't.

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So while we are here let me put on another for loop that is going to tell us what is the class of each

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of the guys in my array.

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So I'm going to go ahead and say for now here's a very interesting thing.

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I don't want to use a numeric for loop I want to use a for loop.

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You know usually if you say four and a string for instance Each my array or so on and so forth.

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But I know the objects in my array are not unnecessary.

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Not only that they could be anything.

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So in a situation like that I'm going to say valid for ID.

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Each in my array it means go through the array.

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Irrelevant of what is inside.

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Then I'm going to say for ID each in my array.

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Let's do this.

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If so what is that for each.

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Is kind of class.

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And what's the class that you're looking for.

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The class is going to be that I'm looking for the ones that are of the type of building I'm going to

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say building class if they are of the type building class here you can do whatever you want to do with

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the building.

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For instance building or turn lights on or anything to that effect.

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So that's about that.

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So we managed to have it respond to select to find out if these objects respond to a certain thing and

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we managed to get the kind of the class that any object is.

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And then depending on that you will end up doing things you could know whether it is or whether it is

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not.

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If you want to filter certain objects out and it's sometimes useful to know what's the kind of the class

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that you are dealing the object that you're dealing with.

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So that's about that for selectors is kind of class.

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Let's move on.