4. Right click on your project.
(or use Shif+Alt+R)
And rename it.
5. In next few slides we are
going to outline general
structure of your App.
6. By opening <src>(stands for
source) ➪ <your package
name>
you will find out your java files
(MainActivity.java)
You can create classes as many
as you want here. (as well as
packages with classes)
They contain code which controls
your application.
7. Next folder we are going to use is
<res> (stands for resource)
1) drawable folders
They contain any pictures you are
using.
2) layout folder
Contain your basic xml layout.
(like html page)
3) values folders
Some constants (mostly strings) used
in your design.
8. Next file you have to work with is
AndroidManifest.xml
Its like a Big Brother, set's up
min/max SDK version your app
going to use,
controls any Permissions and
Instrumentation.
9. You don't need to know anything else to
build simple App yet.
But if you are interested, gen is just a
folder with auto generated files and
Andoid folders contains all library files
we are going to use in our java files.
10. Before we start playing with
code in MainActivity.java
let's set up our layout design
in activity_main.xml file.
11. Good thing is that layout
can be controlled by drug-
and-drop method. So just
click on “Hello World” and
you can simply delete it.
Then just drug into your app
four buttons (which will later
represent arithmetic
symbols)
12. Now by clicking on
activity_main.xml tab at
the bottom you will go into
the “code” of the layout.
Each button is represented
by opening and closing tag
<Button … />
And as parameters you can
change it's text, layout_width
and so on...
android:id sets name which
represents button in a java
file.
Now change text and id
parameters for each
button.
Like in the next slide.
13. Don't worry if your code is a bit
different.
Because of graphical relative
layout android:layout_... might
have different value
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<Button
android:id="@+id/minus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/plus"
android:layout_alignBottom="@+id/plus"
android:layout_alignParentRight="true"
android:layout_marginRight="67dp"
android:text="-" />
<Button
android:id="@+id/division"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/plus"
android:layout_below="@+id/plus"
android:layout_marginTop="47dp"
android:text="/" />
<Button
android:id="@+id/mult"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/division"
android:layout_alignBottom="@+id/division"
android:layout_alignLeft="@+id/minus"
android:text="*" />
<Button
android:id="@+id/plus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:layout_marginLeft="39dp"
android:text="+" />
</RelativeLayout>
14. Now change back to
Graphical Layout and
correct layout by drug and
drop if something doesn't
look beautiful enough.
15. From Form Widgets folder
drug and drop TextView.
(this field will be used to
show the answer)
And from Text Fields drug
and drop Plain Text.
(this will take two numbers
as input)
17. We are finished with a design part, of
course if you don't want anything to
add up upon on this.
Let's do some code in java file
MainActivity.java
To give some life into dead design.
18. I am not going to explain the
way functions work here in
detail yet. (they are
generated automatically)
All we need to know is that
all code inside onCreate is
running when program first
starts.As a first step we need to
create variables which will
represent the value of input
numbers and the final
result.
19. Hence, create three integer
numbers.
In java each variable has a
type.
Integer number has a type of
int.
E.g. integer number with
name firstVar:
int firstVar;
20. Hence, create 4 buttons
variables, 2 EditText and 1
TextView for each layout
item.
As well as to represent
numbers we should set a
type for Button, TextView
and EditText.
E.g. Button with name 'plus':
Button plus;
TextView with name
'answer':
TextView answer;
and so on...
21. As you noticed Button,
TextView and EditText are
underlined this mean that
they have an error.
Eclipse/Android Studio
doesn't understand what
does they mean until we
import library.You can do it by navigating
your mouse on it and
pressing import.
Or you can import them all on Eclipse
by running <ctrl> <shift> <all>➪ ➪
22. Now we need to initialized our
variables, give them value.
We have to do it inside onCreate
function, so we will have them
initialized when app is just created.
In order to initialize Button, EditText
You have to e.g. for button variable
'add':
add = (Button)
findViewById(R.id.plus);
where 'plus' is id we set it up in
layout file.
It is easy to give a value to
int variable, just e.g.
firstVar=0;
23. Create onClickListener for
all buttons.
Now let's set button click listener
for all buttons.
You can do it by adding
.setOnClickListner attribute which
creates implemented method
onClick, which is running when the
button (e.g. plus) is clicked
