Intro to Android Development

with

Parthiban Loganathan

Am I ready to become one with the Android?

(aka prereqs)

You know Java (1004, 1007 is fine)
You own an Android device
You want to build cool apps!

What are we going to do today?

Learn the basic components of a simple Android app
Go over some app code and see the results
Learn about amazing libraries you should use to build apps
Learn how to learn - I'll point you to the best resources for Android

But first...

Let's understand the pros and cons of the Android OS because other mobile platforms do exist... sort of.

Android is fragmented

Different screen sizes

Different OS versions

... leading to frustrated Android developers

Then why Android?

52% of US and 85% of the global mobile market + it's growing
Growing ecosystem - Android Wear, Google Glass

No review process from an evil overlord (cough Apple cough)

Build awesome apps and help the world be a better place!

Dev Environment

You will need:

Android Studio with SDK+AVD Manager (https://developer.android.com/sdk/installing/studio.html)
Android SDK (https://developer.android.com/sdk/installing/index.html?pkg=tools)
USB drivers for your device if applicable

Setup can sometimes be complicated and often machine specific.

Come to Cookies & Code for help.

Main components of an app

Activities (stuff you can see)
Services (happen in background)
Broadcast receivers (react to system broadcasted messages)
Content providers (accessing data)

We will only use Activities today

We will look at

Building a simple UI in XML
Reacting to interactions UI in our Activity
How to store static resources as XML
How to start activities and use external features of the Android OS
A very brief overview of using 3rd party libraries, APIs and networking

Architecture Choices?

Doesn't matter at this stage.

Pick your favorite:

MVC
MVVM
VIPER
JKALDGSDB *

* result of banging head on keyboard

How do I make UIs?

(aka shiny stuff)

Layouts (View Groups): Organize UI elements in XML
You can add Views and widgets to these Layouts to organize UI
Reminiscent of HTML in web development
Android Studio has a GUI builder (but it stinks)

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingTop="10px"
    android:paddingLeft="10px"

    <Button
        android:id="@+id/sample_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@color/white"
        android:background="#50AD21"
        android:text="Click me!" />

</LinearLayout>

A LinearLayout with a Button

Activities

Loosely translates to a single thing you can do. For our purposes, it's a screen.
Many methods like onCreate(Bundle), onPause()
Can load your UI layout
Controllers to react to user interactions
and much more that we're not going to cover here

"Controllers"

React to button presses
Get text from text boxes
Perform API requests

Plain old Java + Android specific methods via interfaces to start new activities, access SharedPreferences, etc.

// Get an object that represents the button view declared in the XML
mButton = (Button) findViewById(R.id.sample_button);

// Set an onClickListener to react to it
mButton.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
    // Do stuff here on click
  }
});

Context

An instance of context lets you access information about the application environment - global parameters, resources like text, images.
Need it to write to disk, get GPS data, access volume, handle intents and more
WARNING: Mishandling context is the biggest source of memory leaks!

Files we will touch

app/src/main/java/com/adi/awesomeapp/MainActivity.java
app/src/main/res/layout/activity_main.xml
app/src/main/res/values/strings.xml
app/src/main/AndroidManifest.xml

* default project structure varies with different versions of Android Studio (it's still in beta)

Let's look at some real code

Step 1

We added a blank MainActivity.java which just loads the UI activity_main.xml
activity_main.xml contains a simple RelativeLayout with a TextView saying "Hello world!" using the resource from strings.xml

Step 2

We modified activity_main.xml to use a ScrollView with an ImageView that loads a picture of a puppy.
Changed the message in the TextView by pointing to a different string resource.

Step 3

We modified activity_main.xml to also contain a Button
In MainActivity.java, we loaded objects referring to the UI components mImage and mButton. We added an onClickListener to the button which creates a camera intent and starts a new activity.
The result of the intent is parsed and if the camera succeeded in taking a picture, we read it from disk and set it to the image view.
We added <uses-feature> to the manifest so that only devices with cameras can download our app on Google Play.

Step 4

I went crazy and added 2 libraries and a bunch of other stuff to let us tweet pictures.

But seriously, the concepts to know are:

Using threads for network requests to not block the main UI thread
How to use 3rd party libraries with the gradle build tool.
How to use features that need permissions (like internet, GPS)

Pro Tips

Remember to handle edge cases - there are a ton of them. Eg - storing state on screen rotation, exiting and resuming app, starting duplicate services by accident, etc.

Learn the Activity Life Cycle

...also applies to some stuff I didn't cover like Fragments

Rule of thumb to avoid memory leaks

Don't use getBaseContext(). Avoid using activity context to prevent memory leaks. Be wary of passing the context around since it won't be garbage collected.
Try getApplicationContext() when possible.