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Welcome back.

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And this video, we're going to implement the under your button, so basically undo button here, you

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can see once you click on that, it will delete the last entry on our drawing board.

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And yeah, let's just implement it.

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Therefore, let's go over to our project.

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And the first thing that I'm going to do is I'm going to duplicate this image button here, and I'm

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going to call this one image button undo.

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And then according to I need to use another image or another trouble, and I have this trouble.

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You can just use any trouble you want.

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I will just use this icy undo.

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You can download the project and get it from there.

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So this will be the page that I'm going to use and I'm going to assign it to my image.

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But and so the idea is that it's going to look like this where we have the gallery here, the image

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button and then the brush size selector, so to speak.

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OK, now let's go ahead and use it.

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In order to use the button, we need to do the same thing the image button.

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We need to do the same thing as we did here with the image button.

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So let me just copy the I b brush.

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And accordingly, this will be I undo.

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Here on do like so fine view by ID and accordingly, we want to assign the on click event for it as

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well.

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So but I'm not going to call the show brush size chooser dialogue, but instead what I want to do is

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I want to call a method that will undo the drawing.

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And here, by the way, this is not ibey brush, but I be undue.

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So that was the idea of our image button, which is this button here?

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OK.

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So where could we do something that has to do with drawing well and our drawing view?

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That's where we created all of our paths, right?

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So there is this empaths variable that is an array list of custom paths and custom paths we saw.

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It's just our own class that we created here as well.

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And now we are going to require is basically going to be the same thing, but one for undue puffs.

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So an ArrayList, that will be a list of custom paths, but we'll just collect or store to undo paths.

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Now accordingly, we just need to create a method that will take care of the undoing.

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And how do we do that?

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Well, basically what we want to do is we want to delete an entry from empaths and we want to store

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it in undo, perhaps.

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OK, so let's create a method for that.

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So fun on click undo.

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So I'm going to call it, and I want to check first if there are any paths even to delete from.

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So only if there are paths, which means if the imperfect size is greater than zero, only then do I

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want to add something to my undo.

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Perhaps.

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And what is it that I want to add to it?

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Well, the path that I'm removing from my empaths, we can do it in one line where we say and perhaps

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remove that and then the index and what is the index that I want to use?

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Well, I basically want to delete the last entry.

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And how do we get the last entry of an array list?

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Well, by using the size of the array list minus one.

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So empaths that size minus one.

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Because what that remove add method does is it returns the item that it removes.

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OK, so we are basically receiving the item that it removes and we are adding it to our undo paths.

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So this by itself would not call the on draw method.

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This one here, which takes care of all of the drawing right, which takes care of drawing all of the

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paths.

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So here and perhaps that's basically all of the custom paths that we created, and that's where it actually

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draws them.

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So what we need to do is we need to call this method once again.

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So this on draw method once again, and we don't call it manually by saying on draw like so.

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But what we can do instead is we call the invalidate method, which will then internally call on draw.

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OK, because this is an override method and this is done for views, right?

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This is a method that exists inside of views because our drawing view is of class type view.

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So it's just going to redraw the entire page.

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So that's what our Click Undo method will do.

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I know we just need to call it.

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And the best spot would be once we click on the button.

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So here in the set on Click Listener, we can just use this method.

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But because this method is in this drawing view class, we need to make sure that we use the drawing

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view here in order to get access to it.

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So here I'm just going to say drawing view dots on click undo.

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So I'm just going to call this method.

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But because drawing viewers and Nullarbor, we need to add the question mark here.

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OK, so now let's go ahead.

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And test this and see if it's going to work, so draw and draw and you see the undo works perfectly.

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And withdraw some more.

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And also with different colors and stuff, and I'll click the back button and you see it works as intended.

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So now you could implement a redo button very easily, you know how to create the undo button.

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Basically, you just need to add back the.

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Here, the last, Andrew, from undue payoffs to impasse, basically with the same approach that you

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have here and then call Invalidate, so I would say try it by yourself.

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Implement this as a little challenge for yourself.

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This will really help you to understand this a little better.

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And good luck with it.

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So in the next video, we're going to look at cold routines, which is a little demo that you will need

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to understand how to run cold in the background.

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And then we're going to look at how we can make a sandwich out of our images because we actually have

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two images here, right?

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The image in the background and what we are drawing.

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All right, so see you in the next video.