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  • Hello, I'm Edu from Edu4Java and this is tutorial number 2 on Android game programming

  • in this tutorial we are going to learn

  • to draw an image

  • in a SurfaceView

  • this is a View

  • of low level which gives us a lot of flexibility and is very efficient which is important for games so that everything happens quickly

  • I am going to make this tutorial following a tutorial which I have in my website

  • edu4java.com

  • so that if anyone get's lost in the way here you have the guide. Let's create a new Android project

  • called killThemall-Training. KillThemall is the name I gave

  • to the

  • small application we are developing

  • this small game

  • ok, here I choose the name of the project

  • Here you can choose what ever you want. We are going to choose the 8. For the application name we are going to name it Killthemall.

  • For the package we are going to put this. Here we are going to write Main

  • And here 7... for compatibility. 7 is for 2.1. With this we can

  • select finish

  • and the project is generated. If you've seen my tutorials in Android you know that a main is generated

  • and also a layout is generated

  • we are not going to use this layout

  • because we want a total control of

  • the application. We are going to interact directly on the view

  • This view instead of coming out of a layout is going to be created by us

  • we create a new

  • gameView

  • I think it was called...

  • we create the class create GameView

  • finish...

  • we have to include the

  • constructors

  • we can choose... we select this one..

  • we are obliged to choose one

  • because of this we have to put this...

  • the view needs a reference to the activity. Here we have the reference to the activity

  • that would be the Context. Let's help us with the page. In the main we don't have to do anything else. In the View

  • we have the context, let's create a bmp

  • un bitmap

  • ehhh

  • let´s put this here

  • create a bitmap

  • we haven't got the bitmap declared so

  • let's first import the other one. Shift+ctrl+o to import

  • and this one

  • let's create a field

  • there it is

  • ctrl+s to save

  • let's go back to the page because I have already forgot what we were doing.Here we created the bitmap

  • afterwards we have to override a method called onDraw

  • this method

  • is going to be called

  • shift+ctrl+o for the import

  • this method is going to be called automatically

  • from the view

  • in fact I don't know if it is a view or a holder.A view is inside a holder. It is like a container

  • this holder manages the view. It tells the view what to do.

  • the holder in the some way runs a code in the view, inside

  • the one we extend and this code must run this onDraw

  • and here is were we can write in the application.This canvas object here

  • is like the blackboard were we could

  • write. Imagine we were at school and we had a blackboard

  • and we could write with a chalk

  • we write through a lot of methods of this canvas. Here we can see it has a lot

  • the first thing I do is tell him to make the background black

  • and afterwards I

  • tell him

  • to

  • print the bitmap

  • this one I had already created

  • in the position 10, 10

  • we will talk about this parameter null later on

  • when I get the bitmap I use this static method from the BitmapFactory

  • and I pass him

  • the resources, which is mainly a view method

  • and this, if you remember from other tutorials, is an icon which comes with the application

  • this icon here

  • this one

  • we are going to use this one to not complicate things. Later on we will use others

  • let's go here

  • run as

  • Android application. You are going to have to wait but I had it already loaded

  • Here it is. As you can see

  • It opened and it printed. This is the bar I didn't wan't. We can take it out

  • with the line

  • this one

  • in the activity

  • if we add this here

  • ctrl+shift+o to import ctrl+s to save

  • and now

  • we run again

  • here it goes again

  • Can you see it disappeared?

  • ok, until now we have been printing with a view, let's try it with a SurfaceView

  • what we have to do is to replace this view with a

  • SurfaceView

  • if we run this we are going to see something wrong

  • that the image doesn't print, because SurfaceView is a lower level class so all that code we were talking about

  • which makes the call to the onDraw

  • we haven't got it now

  • we are going to have to call the method ourselves

  • to call the method

  • we need to know when to call it and also we use the canvas object to call it

  • to do this

  • we should

  • first get the holder and

  • afterwards

  • do a holder callback

  • here we are going to put the

  • holder. There is a holder method in SurfaceView which gives us the holder

  • let's create a

  • field

  • because we are going to use it in the future

  • and here we are going to include a call..

  • we are going to register a...

  • a class

  • which is going to be a listener of the events of the callback of the Holder. Let's ask for help...

  • it gives us the possibility to create an anonymous class

  • which implements the interface SurfaceHolder.callback

  • here there is an error because we have to import the interface

  • this one

  • here it is. This is an inner class

  • This is the same as creating a new class. The only difference is that everything is here altogether

  • so

  • that the object is a listener of the SurfaceHolder

  • we need

  • ehh

  • that the anonymous class implements the methods of the interface callback

  • ehh

  • this methods are

  • destroy

  • which is going to tell us when the view is destroyed, when everything is finished

  • when it is created

  • and when

  • it has a change

  • what we are interested in now, is this one

  • this one...

  • this method is going to be run when the list is prepared to

  • make prints

  • in this method we are going to put this code

  • which what

  • it does is ask the Holder(which comes as a parameter) we also have it as a property but in this case it comes as a parameter

  • It asks the holder through the method lockCanvas. This null is not necessary...

  • it asks for the canvas. Why lockCanvas? this method

  • makes a lock to the Canvas. It reserves it so that nobody

  • else uses it

  • when we have c, we can call the onDraw method

  • with the Canvas

  • after calling the onDraw we have to tell the Holder to unlock it

  • this is important because the locks work against the performance of the application

  • it is very important in games because we are talking of real time

  • let's run this

  • here it comes. Now is does print. We had to do it by hand

  • ok, this is everything for this tutorial

  • I 'll wait for you in the next one!

Hello, I'm Edu from Edu4Java and this is tutorial number 2 on Android game programming

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A2 holder method view ctrl canvas application

Android Game 2 Java Programming tutorial

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    howshin posted on 2013/10/04
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