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GATAV
2. Android-Basics, part 1
TOC
1. The anatomy of an Android project
2. The DDMS perspective
3. Important components of an Android app
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Activities
Layouts
Fragments
Views & Widgets
Intents, part 1
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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The anatomy of an Android project
 The ‚src‘-folder contains the different
Java files (in most cases activities).
 The folder ‚gen‘ contains the automatic
generated file R.java .
 The ‚assets‘-folder for raw files.
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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The anatomy of an Android project
 Inside the ‚bin‘-folder you can find the
app itself and the used resources.
 The folder ‚res‘ holds all the resource
files (e.g. images, layout- and value-files,
sounds, …).
 The ‚AndroidManifest.xml‘
 Configuration files
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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The anatomy of an Android project
 The ‚res‘-folder:
 ‚anim‘ to store animations
 ‚drawable‘ for images
 png, 9.png, jpg, gif
 ‚layout‘ for layout xml-files
 ‚menu‘ for xml-files that define application
menus
 ‚raw‘ to save files in their raw form
 e.g. pdf, mp3, ...
 ‚values‘ for values like strings, colors,
dimensions, arrays, styles, …
 ‚xml‘ for any xml-files that not fit one of the
other categories
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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The DDMS perspective
 DDMS = Dalvik Debug Monitoring Server
 The DDMS allows
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to take screenshots
to terminate processes
to get thread and heap informations
to monitor the logcat
to simulate incoming calls, SMS and geo-locations
to access the file structure on the device
...
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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The DDMS perspective
 The DDMS perspective
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app





Activities
Fragments
Layouts
Views & Widgets
Intents, part 1
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
8
Important components of an Android app
Activities
 An activity represents a single screen with a user
interface
 Example (email application):
 one activity that shows a list of new emails
 one activity to compose an email
 one activity for reading emails
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Activities
 Activities are the base of an Android application
 Activities work together, but each one is independent of
the others
 A different application can start any one of these
activities (if the application allows it)
 e.g., a camera application can start the compose-email-activity
of the email application, so that the user can mail the new
picture.
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Activities
 An activity is implemented as a subclass of Activity
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
/...
}
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Activities
 The activity lifecycle
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Activities
 The activity lifecycle
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Fragments
 Fragments represent portions of a user interface (screen)
in an activity
 Fragments are modular sections of the ui of activities
with own lifecylce and own input events
 Fragments can be efficiently dynamically added and
removed
 Fragments live in the view-hierachy of an activity
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Fragments
 We use one single fragment:
public class MainActivity extends Activity {
/...
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup
container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main,
container, false);
return rootView;
}
}
}
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Layouts
 For every screen resp. activity resp. fragment a layout is stored as
a XML file in the res/layout folder
 All layouts are subclasses of View
 Each element of a layout needs specifications about width and
height
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Layouts
 LinearLayout
 in most cases the preferred layout
 the most flexible layout but also the most expensive
 two orientations: vertical | horizontal
 RelativeLayout
 elements are positioned relative to the border or other elements
 high performance
 examples:
 android:layout_alignParentRight="true"
 android:layout_alignParentBottom="true"
 android:layout_below="@id/..."
 android:layout_toLeftOf="@id/..."
 android:layout_alignTop="@id/..."
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Views & Widgets
 Views: visible elements on a screen
 Widgets: more complex and compound views
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Views & Widgets
From Code:
LinearLayout layout = new LinearLayout(this);
setContentView(layout);
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
LinearLayout.LayoutParams.WRAP_CONTENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
Button btn = new Button(this);
btn.setText("Hallo Welt!");
btn.setLayoutParams(params);
layout.addView(btn);
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Views & Widgets
From XML:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/layout"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button android:text="Hallo Welt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Views & Widgets
 Parameter for view elements:
 android:id="@+id/id_TextView_Main"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="@string/hello"
 android:src="@drawable/gatav_banner"
 ...
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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Important components of an Android app
Intents, part 1
 Intent = (german) Absicht
 With intents, activities can communicate with each other and
transmit data and information
 Two kinds of intents:
 expl. intents:
 the target of the intent is known and defined
 in most cases activities of the same application
 most used contructor: new Intent(context, class)
 impl. intents:
 the target of the intent is unknown
 "I have a task. Who can handle this?"
 most used contructor: new Intent(Action, Uri)
 those intents are handled by applications with a matching intent filter
 if more than one application has a matching intent filter, android provides a
choise
Graphical Apps - The Android View: Prof. Dr. Bender, Prof. Dr. Tronnier
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