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!