Android Game 2 Java Programming tutorial

Uploaded by edu4java on 09.04.2011

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
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
I think it was called...
we create the class create GameView
we have to include the
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
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
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
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
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
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
that the object is a listener of the SurfaceHolder
we need
that the anonymous class implements the methods of the interface callback
this methods are
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!