Quick Intro to Android Programming

Quick Intro to Android Programming Jussi Pohjolainen Tampere University of Applied Sciences

HELLO WORLD

Template package fi.somecompany.helloworld;….public class MainScreen extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Creates setContentView(R.layout.activity_main_screen); layout from } xml-‐ﬁle @Override public boolean onCreateOptionsMenu(Menu menu) { getMenuInflater().inflate(R.menu.activity_main_screen, menu); return true; }}

ModiﬁcaDon package fi.tamk;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 public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); TextView tv = new TextView(this); tv.setText("Hello, Android"); setContentView(tv); }}

Running

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 { /** Called when the activity is first created. */ @Override Inner class public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); }} Name of R – class. your xml-‐ Generated for ﬁle(main.xml you )

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 automaDcally by the Eclipse plugin •  R – class: gen/some.package/R.java

R -‐ class •  R – class is an index to package fi.tamk; all your resources public final class R { public static final class attr { } public static final class drawable { public static final int icon=0x7f020000; •  Short way of } referencing to public static final class layout { public static final int main=0x7f030000; resources } public static final class string { public static final int •  Never edit this ﬁle by app_name=0x7f040001; public static final int hello=0x7f040000; 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=".MainScreen" /></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 Handling public 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" > <TextView android: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" /> <Button android: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 automaDcally 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; 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 DelegaDon Event Model •  SeparaDon between applicaDon 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

And the Java Code

LOGCAT

logcat •  CollecDng and viewing system debug output •  Command line app –  adb logcat•  Can be opened also in Eclipse –  Window > Show View > Other… > Logcat

Eclipse and logcat

Reading and WriDng Logs •  Log is a logging class for prin<ng 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”);

Logcat outputs everything

Filtering Output •  Log message contains –  Tag – short String –  Priority – following chars from lowest to highest priority: v(erbose), d(ebug), I(nfo), w(arning), e(rror), f(atal), s(ilent)•  Example output –  D/MainScreen( 903): User clicked some view object: android.widget.Button@411fe148•  Priority level is D and tag is MainScreen

RestricDng output •  To restrict output, use ﬁlter expressions •  Format –  tag:priority – priority is the minimum level of priority to report •  You can give several expressions, whitespace delimited •  Example –  adb logcat -s tag1:priority1 tag2:priority2

Real World Usage •  Example –  $ adb logcat –s MainScreen:D –  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 PracDce •  Published app should not contain logging code •  BuildConﬁg.DEBUG ﬂag is here to help! •  Flag is set automaDcally to false, when exporDng 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 codeDebug.print("MainScreen", "Something");

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Quick Intro to Android Programming

by Jussi Pohjolainen

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