Quick  Intro  to  Android  Development

Jussi Pohjolainen

Android  Studio

• Android  Studio  replaces  Eclipse  as  Google’s  primary  IDE for  native  Android  Development

• Features–WYSIWYG  Editor– Template  wizards– Support  for  Android  Wear– Lint  tools– Etc

Templatepublic class MainScreen extends ActionBarActivity {

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

getMenuInflater().inflate(R.menu.activity_main_screen, menu);

return true;

}

}

Creates  layout  from  xml-­‐file

Modificationimport android.app.Activity;

import android.os.Bundle;

import android.widget.TextView;

public class Main extends Activity {

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

TextView tv = new TextView(this);

tv.setText("Hello, Android");

setContentView(tv);

}

}

Running

Running

UI:  By  Coding  or  XML

• You  can  code  your  UI  or  you  can  use  XML  – files

• Using  XML  – files  is  the  preferredway

• File  res/layout/foo.xmlcontains  the  basic  template  for  your  UI

Using  the  XML  filepackage fi.tamk;

import android.app.Activity;

import android.os.Bundle;

public class Main extends Activity {

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

}

}Name  of  your  xml-­‐

file(main.xml)

R  – class.  Generated  for  

you

Inner  class

XML  and  R  -­‐ class

• XML  file  will  be  compiled  to  a  Java  object• Reference  to  that  object  is  made  through  R  –class

• R  – class  is  generated  automatically  by  the  Eclipse  plugin

• R  – class:  gen/some.package/R.java

R  -­‐ classpackage fi.tamk;

public final class R {public static final class attr {

}

public static final class drawable {public static final int icon=0x7f020000;

}

public static final class layout {

public static final int main=0x7f030000;}

public static final class string {

public static final int app_name=0x7f040001;public static final int hello=0x7f040000;

}

}

• R  – class  is  an  index  to  all  your  resources

• Short  way  of  referencing  to  resources

• Never  edit  this  file  by  hand!

XML  -­‐ file<RelativeLayoutxmlns: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" >

<TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_centerHorizontal="true"android:layout_centerVertical="true"android:text="@string/hello_world"tools:context=".MainActivity" />

</RelativeLayout>

XML  – file,  without  Name  Spacing

<?xml version="1.0" encoding="utf-8"?>

<TextView layout_width="fill_parent"

layout_height="wrap_content"

text="@string/hello_world"/>

Reference  to  res/values/strings.xml

res/values/strings.xml<resources>

<string name="app_name">MyHelloWorld</string>

<string name="hello_world">Does this work?</string>

<string name="menu_settings">Settings</string>

<string name="title_activity_main_screen">MainScreen</string>

</resources>

Result

Two  Widgets  and  Event  Handlingpublic class Main extends Activity implements OnClickListener {

private Button clickMe;

private TextView textView;private LinearLayout layout;

public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);

clickMe = new Button(this);

clickMe.setText("Click Me!");clickMe.setOnClickListener(this);

textView = new TextView(this);textView.setText("Some Text");

layout = new LinearLayout(this);layout.addView(clickMe);

layout.addView(textView);

setContentView(layout);

}

public void onClick(View v) {

textView.setText("Clicked!");

}}

Two  Widgest and  Event  Handling  via  XML<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" >

<TextViewandroid:id="@+id/textView1"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_centerHorizontal="true"android:layout_centerVertical="true"android:text="@string/hello_world"tools:context=".MainScreen" />

<Buttonandroid:id="@+id/button1"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_below="@+id/textView1"android:layout_centerHorizontal="true"android:text="Change text" />

</RelativeLayout>

R  – class  updates  automaticallypublic final class R {

public static final class attr {

}

public static final class drawable {

public static final int ic_action_search=0x7f020000;

public static final int ic_launcher=0x7f020001;

}

public static final class id {

public static final int button1=0x7f070001;

public static final int menu_settings=0x7f070002;

public static final int textView1=0x7f070000;

}

public static final class layout {

public static final int activity_main_screen=0x7f030000;

}

public static final class menu {

public static final int activity_main_screen=0x7f060000;

}

public static final class string {

public static final int app_name=0x7f040000;

public static final int hello_world=0x7f040001;

public static final int menu_settings=0x7f040002;

public static final int title_activity_main_screen=0x7f040003;

}

public static final class style {

public static final int AppTheme=0x7f050000;

}

}

..  And  the  Codepublic class Main extends Activity implements OnClickListener {

private Button clickMe;private TextView textView;

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

clickMe = (Button) findViewById(R.id.button1);textView = (TextView) findViewById(R.id.textView1);

clickMe.setOnClickListener(this);}

public void onClick(View v) {textView.setText("Clicked!");

}}

About  Delegation  Event  Model

• Separation  between  application  and  UI  code• Example:  

– somebutton.setOnClickListener(OnClickListener);

• Source:  somebutton• Listener:  some  object  that  implements  OnClickListener

• There  is  a  easier  way  to  do  basic  event  handling..

Listeners  in  XML<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"android:layout_width="fill_parent"android:layout_height="fill_parent">

<Button android:text="Click 1" android:id="@+id/button1"android:layout_width="fill_parent"android:layout_height="wrap_content"android:onClick="click" />

<Button android:text="Click 2" android:id="@+id/button2"android:layout_width="fill_parent"android:layout_height="wrap_content"android:onClick="click" />

</LinearLayout>

And  the  Java  Codepublic class EventHandlingDemo extends Activity {

/** Called when the activity is first created. */@Overridepublic void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);setContentView(R.layout.main);

}

public void click(View source) {switch ( source.getId() ) {

case R.id.button1:

// do something

break;

case R.id.button2:

// do something

break;}

}}

LOGCAT

logcat

• Collecting  and  viewing  system  debug  output• Command  line  app– adb logcat

• Can  be  opened  also  in  Eclipse– Window > Show View > Other… > Logcat

Android  Studio  and  Logcat

Reading  and  Writing  Logs

• Log is  a  logging  class  for  printing stuff  to  logcat– Common  methods:  

• v(String, String) - verbose

• d(String, String) - debug

• i(String, String) - info

• w(String, String) - warning

• e(String, String) – error

– Example• Log.d(“MainScreen”, “Just printing stuff”);

• logging

Logcat outputs  everything

Filtering  Output

• Log  message  contains– Tag – short  String,  example  "MainScreen"– Priority– following  chars  from  lowest  to  highest  priority:  • v(erbose) – lowest priority

• d(ebug)• i(nfo)

• w(arning)

• e(rror)• f(atal)• s(ilent) – highest priority, nothing is printed

Filtering  Output

• Example  output– D/MainScreen( 903): User clicked some view object: android.widget.Button@411fe148

• Priority  level  is  D  and  tag  is  MainScreen

Restricting  output

• To  restrict  output,  use  filter  expressions• Format– tag : priority

– priority  is  the  minimum  level  of  priority  to  report

• Example– adb logcat

– tag1:priority1 // show this and..

– tag2:priority2 // this..

– *:S // Set all other tags silent

Real  World  Usage

• Example– $ adb logcat MainScreen:D *:S

– D/MainScreen( 903): User clicked some view object: android.widget.Button@411fe148

• Display  output  from  MainScreen tag  with  priority  debug  or  above  and  restrict  everything  else

From  Eclipse

Good  Practice

• Published  app  should  not  contain  logging  code• BuildConfig.DEBUG flag  is  here  to  help!• Flag  is  set  automatically  to  false,  when  exporting  your  app

• How?– if(BuildConfig.DEBUG) { Log.e(…); }

Create  a  Debug  Class!package fi.tamk.tiko.pohjolainen.utilities;

class Debug {

public static void print(String tagName, String msg) {

if(BuildConfig.DEBUG) {

Log.d(tagName, msg);

}

}

}

// And in code

Debug.print("MainScreen", "Something");