Android – A First Program

1. Android – A First Program L. Grewe

2. Using AndroidStudio –basic Android • Lets do a “Hello World Project” • Start up AndroidStudio (assume you have installed with Android support)

3. Hello World Project – Android Studio • App name, package • Target • Activity type • Name of Activity • Now finish to setup

4. Hello World Project---basic folders &files Folders • Number of folders and files are auto-generated when you create a project File of note AndroidManifest.xml – like a ship’s manifest it tells us the components of our app

5. Project basics….Android Studio • manifests/AndroidManifest.xml: an XML file describing the application being built and what components – activities, services, etc. – are being supplied by that application • java/: holds the Java source code for the application • res/: contains • layout files • drawable =icons • menus • values = static files like strings.xml • Gradle/: an Ant script for compiling the application and installing it on the device (integrated with IDE—don’t see it there) • default.properties: a property file used by the compiler • res/ – contains multiple xml files and other resources used by application

6. Project basics….Android Studio • Gradle Scripts/: an gradle script for compiling the application and installing it on the device (integrated with IDE—don’t see it there) • gradle.properties: a property file used by the compiler

7. Manifest file – AndroidManifest.xml • an XML file describing the application being built and what components – activities, services, etc. – are being supplied by that application • Initially created by IDE • must declare all activities, services, broadcast receivers and content provider of the application. • must contain the required permissions for the application. • For example if the application requires network access it must be specified here.

8. Hello World Project – AndroidManifest.xml Define Application –see res/strings.xml Manifest file <?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"      package="com.example.helloworldandroid"      android:versionCode="1"      android:versionName="1.0">    <application android:icon="@drawable/icon" android:label="@string/app_name">        <activity android:name=".HelloWorldAndroid"                  android:label="@string/app_name">            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application>    <uses-sdk android:minSdkVersion="4" /></manifest> –see res/drawable-resolution/icon.png Here have intent created for This acitivity that is associated with launch of application

9. The Layout Interface specifications

10. Interface ---2 options • Do it with XML file(s) • Many modern frameworks whether for mobile programming like Android or iOS or for other platforms have gone to specifying GUI (graphical user interface) elements in static XML files rather than programming source code (like java). • The reason –it allows separation of the look (view) from how the code works (model and controller). Have you ever heard of Model View Controller –it is a famous software engineering framework that programmers try to achieve in their software systems. • Do it with Java code. • This has similarities if you have created desktop GUI Java applications

11. OPTION 1: The Layout with XML • We are going to discuss a specific resource in the res folder res/layout/activity_main.xml

12. The Layout-the interface • res/layout/main.xml = contains layout for interface <?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" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> </LinearLayout> The above will create an interface in vertical (versus portrait) mode that fills the parent Both in width and write and wraps and content as necessary.

13. The Layout-the interface • res/layout/main.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" > • android:orientation = vertical (versus portrait) mode. • that fills the parent both in width and write and wraps and content as necessary. Vertical Landscape

14. Creating a Layout file—2options • Do it manually –type it in • For Layouts corresponding to GUIs • You have a drag and drop optionwe will learn about in a later lecture Hello World Project Layout file <?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"    ><TextView      android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:text="@string/hello"    /></LinearLayout> This adds a “TextView” to the interface and this has the text referenced by @string/hello in it.

15. Using IDE to Visually Create XML file • Visual creation of XML file • AndroidStudio: New->Layout resource file • Select layout (root) • &qualifiers as needed • drag & drop

16. Visually Creating XML interface • I dragged and dropped an EditText view and a Button. Below I show you the corresponding code. res/layout/main2.xml <?xml version="1.0" encoding="utf-8"?> <AbsoluteLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <EditText android:text="@string/hello" android:id="@+id/editText1" android:inputType="textMultiLine" android:layout_width="169dp" android:layout_height="115dp" android:layout_x="11dp" android:layout_y="20dp"></EditText> <Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Button" android:layout_x="27dp" android:layout_y="146dp"></Button> </AbsoluteLayout>

17. Lets look at the “Main” class It is an Activity Activity is a class in the Android sdk (android.app.Activity) It represents us now the main application itself—we will learn more about what this means in a near future lecture –remember we are at the beginning!

18. Create an Activity with simple text Interface ……first • An Android user interface is composed of hierarchies of objects called Views. • A View is a drawable object used as an element in your UI layout, such as a button, image, or • In the next code will create a text label. Each of these objects is a subclass of the View class and the subclass that handles text is TextView.

19. Hello World Project – here we are creating interface with programatically/code • create a TextView with the class constructor, • which accepts an Android Context instance as • its parameter. • Context is a handle to the system • provides services like resolving resources, • obtaining access to databases and preferences, etc. • The Activity class inherits from Context, and because • your HelloAndroid class is a subclass of Activity, it is • also a Context. So, you can pass this as your Context • reference to the TextView. • text content is set with setText(CharSequence) • pass the TextView to setContentView() in order to display • it as the content for the Activity UI. Helloworld.java • package com.teach.helloworld;import android.app.Activity;import android.os.Bundle;public class helloworld extends Activity {    /** Called when the activity is first created. */    @Overridepublic void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); TextViewtv = new TextView(this); tv.setText("Hello, Android.....Lynne"); setContentView(tv); }}

20. What we just learned • You will have a class created for you that is your android application, i.e. “ helloworld” and it extends Activity • Your application is an Activity and that also descends from Content • Context = class that gives us access to System • provides services like resolving resources, • obtaining access to databases and preferences, etc • View = is a GUI element, there are different kinds like the TextView we are using • .constructor needs Context instance (we used our App)

21. R.java Automatically created by IDE when created project

22. Hello World Project R.Java == generated by project, this points to various resources in your project see res folder. DO NOT EDIT THIS –unless you know what you are doing. /* AUTO-GENERATED FILE. DO NOT MODIFY. * * This class was automatically generated by the * aapt tool from the resource data it found. It * should not be modified by hand. */ package com.example.helloworldandroid; public final class R { public static final class attr { } public static final class drawable { public static final int icon=0x7f020000; } public static final class id { public static final int button1=0x7f050001; public static final int editText1=0x7f050000; } public static final class layout { public static final int main=0x7f030000; public static final int main2=0x7f030001; } public static final class string { public static final int app_name=0x7f040001; public static final int hello=0x7f040000; } }

23. TIP: sometimes when you are compiling your code you can have problems with the R.java file (which you DON’T edit) –what is going on? Somehow the R.java is out of sync with the project resources…..WHAT TO DO? do a “Build->Clean Project” and it will regenerate R.java for you Why have R.java? It is used it in your code to point to resources. Lets look at an example where we alter our onCreate method to point to the interface described in the res/layout/main.xml file….so now interface specified with XML and not programmatically with code.

24. Where is R.java Eclipse: gens/R.java Android Studio: build/generated/source/r/debug/your-package -name/R.java (Example: C:\Users\Lynne\AndroidStudioProjects\HelloWorldAndroid\app\build\generated\source\r\debug\com\example\lynne\helloworldandroid) Android studio: you can not seethe R.java in IDE Go to file system

25. Alter your Activity to Use an XML layout file • package com.example.helloandroid;import android.app.Activity;import android.os.Bundle;public class HelloAndroid extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState); setContentView(R.layout.main);    }} Now going to change thecode so it uses instead anXML file for its intervace This line of code saysuse the xml layout file calledmain.xml that is pointed toinside your R.java file in memory

26. Interfaces ---XML-based layout • Previous HelloWorld example has interface created in java code. • ALTERNATIVE: XML-based layout files. Example that duplicates previous. • <?xml version="1.0" encoding="utf-8"?> <LinearLayout……….> <TextView xmlns:android="http://schemas.android.com/apk/res/android"   android:layout_width="fill_parent"   android:layout_height="fill_parent"   android:text="@string/hello"/> Above located in res/layout/main.xml Here is our main.xml filethat will be used and do the same thing as our previous java code –showa TextView

27. Lets understand the XML Tag used to describe our TextView XML interface • <TextView xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="fill_parent"  android:layout_height="fill_parent"  android:text="@string/hello"/> • xmlns:android XML namespace declaration that tells the Android tools that you are going to refer to common attributes defined in the Android namespace. The outermost tag in every Android layout file must have this attribute. • android:layout_width This attribute defines how much of the available width on the screen this View should consume. As it's the only View so you want it to take up the entire screen, which is what a value of "fill_parent" means.android:layout_height This is just like android:layout_width, except that it refers to available screen height. • android:text This sets the text that the TextView should display. In this example, you use a string resource instead of a hard-coded string value. The hello string is defined in the res/values/strings.xml file. Wow! That’s a lot to remember ---aren’t you glad we have an API online to look it up ---better yet is the drag and drop option to make interfaces!!!

28. More on resources The res directory

29. We mentioned res folder Android Studio

30. res/ directory • res/layout/ : contains one or more xml files that define interfaces • res/values/strings.xml : file where you specify strings (constants) that you can use in your program • res/drawable-* : gives file use for different resolutions like icon.jpg. *=hdpi (high), mdpi(medium), ldpi (low). Depends on device what mode it can/may be running in. • res/menu/ : contains one or more xml files for menus

31. Event Handling So we have an interface what can we do with it. Event Handling = code that responds when “events” happen. For GUI elements we usually have events associated with them. For example, a button has the event of hitting the button.

32. Widget : Views that have events • For a list of the widgets provided by Android, see the android.widget package. • Some Examples • Button • CheckBox • DatePicker • EditText • ImageView • SearchView • Spinner There are more ---here are a few.

33. 3 steps: • Decide what events to respond to • Create a listener to respond to each event • Register the listener to the corresponding widget Event Handling • Decide what Widgets who’s events to process • Define an event listener and register it with the View. • View.OnClickListener (for handling "clicks" on a View), View.OnTouchListener (for handling touch screen events in a View), and View.OnKeyListener (for handling device key presses within a View) • http://developer.android.com/guide/topics/ui/ui-events.html details more

34. Lets add a Button to a program-based interface • Step 1: Add button • Step 2: Register Event Handler • TWO OPTIONS – separate class to handle event(s), OR have the Activity containing the button do the event handling • Step 3: Implement Event Handler…for a Button means implementing the View.OnClickListener interface

35. Event handling done by Activity itself –one option • Here code to handle is inside Activity itself • public class ExampleActivity extends Activity implements OnClickListener {    protected void onCreate(Bundle savedValues) {... Button button = (Button)findViewById(R.id.corky);        button.setOnClickListener(this);    } // Implement the OnClickListener callback    public void onClick(View v) {      // do something when the button is clicked    }    ...} This option is okay only if the event handling code is simple and you will not reuse it ever ---if the code is longer or will reuse make a separate class

36. Event Handling - here have a SEPARATE class EVENT HANDLING CODE in separate object mCorkyListner // Create an anonymous implementation of OnClickListenerprivate OnClickListener mCorkyListener = new OnClickListener() {    public void onClick(View v) {      // do something when the button is clicked    }}; //Now inside your Activity classprotected void onCreate(Bundle savedValues) {    ...// STEP 1: Capture our button from layout    Button button = (Button)findViewById(R.id.corky);// STEP 2: Register the onClick listener with the implementation above    button.setOnClickListener(mCorkyListener);    ...} Better for readability and reuse

37. Run your code Depends on IDE

38. Running code • Will Run in the Emulator • Android Studio: Run->”Run app” or “Debug App” You should learn to run both on the emulator AND on a physical device. TO use features of a phone like GPS, etc. it is often required to run on a phone

39. Running code • TIP: Emulator can take a long time to load at first----be patient and keep it up---just re-run after changes and won’t have to relaunch emulator, will just load up new app. • Look if you have Intell Virtualization speed up, check out GPU and snapshot options –search online for current info on these tips