Basic elements

• Activity
• Intent
• Context
• Layout
• Manifest

There is more...

• Service
• Multimedia
• User info & location
• User input
• Content sharing
• Performance
• Google Cloud Messaging
• Hardware components
• User Interface
• Testing
• Distribution

...and bleeding edge stuff

• Android Studio (still) beta
• Android L
• Wearables
• Google TV
• Google Glass
• Android Auto

Intent intent = new Intent(this, MyActivity.class);
startActivity(intent);

Starting Activity with an Intent

from Context of another activity

Context of the Activity

Context of the Application

public class MyActivity extends Activity {
    public void showMyToast() {
        Toast.makeText(this, "I am toast!", Toast.LENGTH_SHORT).show();
    }
}

// Assuming, we have created BaseApplication class extending Application class
Resources resources = BaseApplication.getInstance().getResources();
String myString = resources.getString(R.string.my_string);

We should use it in operations related to Activity and UI

<!-- part of AndroidManifest.xml file -->
<application android:name="com.app.BaseApplication">

We should use it while accessing elements related to whole application and global elements

LinearLayout

RelativeLayout

TextView, Button, EditText, CheckBox, RadioButton, ImageView, GridView, ListView, ProgressBar and many more...

We can also create our own custom views!

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical" >
    <TextView android:id="@+id/text"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Hello, I am a TextView" />
    <Button android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello, I am a Button" />
</LinearLayout>

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_layout);
}

Exemplary

Layout

Layout initialization

in Activity

res/layout/main_layout.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="string"
          android:versionCode="integer"
          android:versionName="string"
          android:installLocation=["auto" | "internalOnly" | "preferExternal"] >

 <uses-permission />
    <permission />
    <uses-sdk />
    <supports-screens />  
    <compatible-screens />

    <application>
        <activity></activity>       
        <service></service>
        <receiver></receiver>
        <provider></provider>
    </application>

</manifest>

Describes application

package, version, SDK, activities, services, receivers, providers, etc.

AndroidManifest.xml syntax with the most important features

Retrofit

public interface GitHubService {
  @GET("/users/{user}/repos")
  List<Repo> listRepos(@Path("user") String user);
}

RestAdapter restAdapter = new RestAdapter.Builder()
    .setEndpoint("https://api.github.com")
    .build();

GitHubService service = restAdapter.create(GitHubService.class);

List<Repo> repos = service.listRepos("octocat");

Dealing with many scenarios and many conditions

• Creating so called NavigationDispatcher
• Defining flow steps in JSON file
• Flow steps objects are created with Java reflection
• GSON library is used for transforming JSON data into objects
• Single step consists of: originatingContext, action, factories.

Profits?

Approach

Problem

• We send request
• We don't know, when will we receive the response

Approach #1

AsyncTask and Callback

Approach #2

How about events?

tight coupling

Otto Event Bus

loose coupling

Bus bus = new Bus();
bus.post(new AnswerAvailableEvent(42));

@Subscribe 
public void answerAvailable(AnswerAvailableEvent event) {
    // TODO: React to the event somehow!
}

Micro-location using WiFi Access Points

Check out open-source library:  

https://github.com/pwittchen/NetworkEvents (still under development)

Injecting views

class ExampleActivity extends Activity {
  @InjectView(R.id.title) TextView title;
  @InjectView(R.id.subtitle) TextView subtitle;
  @InjectView(R.id.footer) TextView footer;

  @Override public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.simple_activity);
    ButterKnife.inject(this);
    // TODO Use "injected" views...
  }
}

public void inject(ExampleActivity activity) {
  activity.subtitle = (android.widget.TextView) activity.findViewById(2130968578);
  activity.footer = (android.widget.TextView) activity.findViewById(2130968579);
  activity.title = (android.widget.TextView) activity.findViewById(2130968577);
}

Butter Knife

This code:

will generate this code (instead of using slow reflection):

RoboGuice

Dagger

• is popular
• used by well known apps (e.g. Facebook Messanger)
• easy to use
• has many features
• is slow, because uses reflection

• is less popular
• does not have all features of RoboGuice
• is fast, due to compile-time code generation

In mobile applications development Dagger would be a better choice as DI framework, because in this case, speed matters.

Picasso

Picasso.with(context).load("http://i.imgur.com/DvpvklR.png").into(imageView);

Service

IntentService

<manifest ... >
  <application ... >
      <service 
         android:name=".HelloService" />
  </application>
</manifest>

public class HelloIntentService extends IntentService {
  public HelloIntentService() {
      super("HelloIntentService");
  }

  @Override
  protected void onHandleIntent(Intent intent) {
    // start executing operation here
  }
}

public class HelloService extends Service {
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // start executing operations here
        return super.onStartCommand(intent,flags,startId);
    }
}

HelloService.java

HelloIntentService.java

AndroidManifest.xml