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Quick Intro to Android Development
This document provides a quick introduction to Android development. It discusses Android Studio as the primary IDE for Android development and its features. It also covers templates, running apps, building UIs with code and XML, using resources and the R class, basic event handling, Logcat for viewing logs, and best practices for logging.
Quick Intro to Android Development
- 1. Quick Intro to Android Development Jussi Pohjolainen
- 2. 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
- 6. Template public class MainScreenextends 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
- 7. Modification import android.app.Activity; import android.os.Bundle; importandroid.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); } }
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- 10. 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
- 11. 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 public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } } Name of your xml-‐ file(main.xm l) R – class. Generated for you Inner class
- 12. 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
- 13. R -‐ class packagefi.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!
- 14. 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>
- 15. 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
- 16. res/values/strings.xml <resources> <string name="app_name">MyHelloWorld</string> <string name="hello_world">Doesthis work?</string> <string name="menu_settings">Settings</string> <string name="title_activity_main_screen">MainScreen</string> </resources>
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- 18. 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!"); } }
- 19. 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>
- 21. 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; } }
- 22. .. 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!"); } }
- 23. 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..
- 24. Listeners in XML <?xmlversion="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>
- 25. And the Java Code public class EventHandlingDemo extends Activity { /** Called when the activity is first created. */ @Override public 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; } } }
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- 27. logcat • Collecting and viewing system debug output • Command line app – adb logcat • Can be opened also in Eclipse – Window > Show View > Other… > Logcat
- 28. Android Studio and Logcat
- 29. 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
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- 31. 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
- 32. Filtering Output • Example output – D/MainScreen( 903): User clicked some view object: android.widget.Button@411fe148 • Priority level is D and tag is MainScreen
- 33. 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
- 34. 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
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- 36. 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(…); }
- 37. 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");