Quick Intro to Android Development

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

Template
public 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

Modification
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class Main extends Activity {
/** Called when the activity is first created. */
@Override
TextView tv = new TextView(this);
tv.setText("Hello, Android");
setContentView(tv);
}
}

UI: By Coding or XML
• You can code your UI or
you can use XML – files
• Using XML – files is the
preferred way
• File
res/layout/foo.xml
contains the basic
template for your UI

Using the XML file
package fi.tamk;
import android.app.Activity;
import android.os.Bundle;
public class Main extends Activity {
@Override
setContentView(R.layout.main);
}
}
Name of
your xml-‐
file(main.xm
l)
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 -‐ class
package 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
<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" >
<TextView
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=".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>

Two Widgets and Event Handling
public class Main extends Activity implements OnClickListener {
private Button clickMe;
private TextView textView;
private LinearLayout layout;
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" >
<TextView
android:id="@+id/textView1"
android:layout_centerVertical="true"
android:text="@string/hello_world"
tools:context=".MainScreen" />
<Button
android:id="@+id/button1"
android:layout_below="@+id/textView1"
android:text="Change text" />
</RelativeLayout>

R – class updates automatically
public 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 Code
public class Main extends Activity implements OnClickListener {
private Button clickMe;
private TextView textView;
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:onClick="click" />
<Button android:text="Click 2" android:id="@+id/button2"
android:onClick="click" />
</LinearLayout>

And the Java Code
public class EventHandlingDemo extends Activity {
@Override
}
public void click(View source) {
switch ( source.getId() ) {
case R.id.button1:
// do something
break;
case R.id.button2:
// do something
break;
}
}
}

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

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

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");

Quick Intro to Android Development

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