Android Tutorial

Android Written in Java Utilizes Dalvik VM – Just in time (JIT) compilation since Android 2.2

Java Tips Similar syntax to C/C++ All function/procedure arguments passed in by value – Class objects are references that are passed by value No support for multiple inheritance Does support multiple interfaces Garbage collected (Hooray!) – Beware! Can still create memory leaks!

Java Tips All methods are virtual by default Java naming convention

Java Memory Leaks Every class object is a reference to the object Java VM keeps track of reference counts to every object Once nothing refers to an object anymore it gets garbage collected Once finished with an object, set it to null to release the memory

Android Components Activity – Code that has a user interface associated with it – Implemented as a stack Service – Code that runs in the background without a user interface Broadcast Receiver – Code that runs in response to Android OS or Application intents(messages)

Android Components (cont.) Content Providers – Database that is exposed to all applications to consume Intents – Messages that are passed throughout the Android OS/ other applications

Building Android Applications Create UI using XML – New UI dev tools make building UIs awesome Once an xml file is saved, the Eclipse ADT tools create an R.java DO NOT MODIFY R.java!! – Never a good idea, ever like fo realz

Building Android Applications Reference UI elements by utilizing findViewById(int) member method on View object – Ex. – Button b = (Button)findViewById(R.id.myButton); findViewById is expensive!

Starting New Activities Intent i = new Intent(); i.setClass(callingActivity.this, calleeActivity.this); startActivity(i);

Passing objects to Activities Easiest way, just create a static data structure – Accessible to all activities within an application Pass objects through bundles in an intent – Intent i = new Intent(); – i.putExtra(key, stringValue); Retreive object – Bundle b = getIntent().getExtras(); – String o = b.getString(key);

Passing values to Activities Can pass primitive types through bundles – char, int, float, double, String Can pass custom objects by implementing Parcelable interface – os/Parcelable.html os/Parcelable.html

Be careful of ANRs! ANR = Application Not Responding Occurs when application is not responsive to touch events for ~5 seconds All major computation should be done on a separate thread – Use threads Need a runnable object to update the UI thread – AsyncTask ask.html ask.html

Running Android Apps Can use Android emulator – Obnoxiously slow – Better emulator coming soon, not quite sure when Debugging on device is king!

Building Apps for Varying Devices Java code same (mostly) Add additional xml layout files for each device Save in corresponding directories – layout-land Folder for landscape view – layout-mdpi Folder for layouts for devices with medium density displays

Building Apps for Varying Devices Save copies of same image in different resolutions in drawable folders – drawable-hdpi – drawable-mdpi – drawable-ldpi

Android Extra Fun Stuff Renderscript – New library of APIs that allows for easy animation creation – Also useful for complex computation ADK – Accessory Development Kit – Allows for development of accessories that interface with devices through USB – Based off of Arduino NDK (native development kit) – JNI (Java Native Interface) – Allows for glue between Java and C code for extra performance – Note just writing your application in C++ using the NDK doesn’t make it faster than normal Java implementation

Hints Tips Tricks Android.com Google IO Sessions – html html Android developer blog – Stackoverflow google