1. Android Development
1.1. Android Operation System
Android is an operating system based on Linux with a
Java
programming interface. It provides tools, e.g. a compiler, debugger
and a device emulator as well as its own Java Virtual machine
(Dalvik
Virtual Machine - DVM). Android is
created by the
Open Handset
Alliance which is lead
by
Google.
Android uses a special Java virtual machine (Dalvik) which is
based on the Apache Harmony Java implementation. Dalvik uses
special
bytecode. Therefore you cannot run standard Java bytecode on Android.
Android provides a tool "dx" which allows to convert Java Class
files
into "dex" (Dalvik Executable) files. Android applications are then
packed into an .apk (Android Package) file.
Android supports 2-D and 3-D graphics using the OpenGL
libraries
and supports data storage in a SQLLite database.
For development Google provides the Android Development Tools
(ADT) for Eclipse
to develop Android applications.
Every Android applications runs in its own process and it
isolated from other running applications. Therefore on misbehaving
application cannot harm other Android applications.
1.2. Important Android terms
An Android application consists out of the following parts:
-
Activity - A screen in the Android application
-
Services - Background activities without UI
-
Content Provider - provides data to applications, Android
contains a SQLLite DB which can
serve as data provider
-
Broadcast Receiver - receives system messages, can be used
to react to changed conditions in the system
Intends allow the application to
request and / or provide
services . For
example the application call
ask via an intent for a
contact
application. Application register
themself via an IntentFilter.
Intends are a powerful concept as they allow to create loosely
coupled applications.
An Android application is described the file
"AndroidManifest.xml". This files contains all activities
application
and the required permissions for the application. For example if
the
application requires network access it must be specified here.
"AndroidManifest.xml" can be
thought as the deployment descriptor for
an Android application.
1.3. Activities and Layouts
The user interface for Activities is defined via layouts. The
layout defines the UI elements, their properties and their
arragement. A layout can be defined via XML and via code at runtime.
The XML way
is usually preferred for a fixed layout while defining the
layout via code is more flexible. You can also mix both approaches.
1.4. Activities and Lifecyle
The operating system controls the life cycle of your
application. At
any time the Android system may stop or destroy your
application, e.g.
because of an incoming call. The Android system
defines a life cycle
for an activities via pre-defined methods. The most important methods
are:
-
onSaveInstanceState() - called if the activity is stopped.
Used to save data so that the activity can restore its states if
re-started
-
onPause() - always called if the Activity ends, can be used
to release ressource or save data
-
onResume() - called if the Activity is re-started, can be
used to initiaze fields
The class android.content.Context provides the connections to
the Android system. Contexts provides the method getSystemService
which allows to receive a manager object for the different hardware
parts. As Activities and Services extend this class you
can directly
access the context via "this".
The following assume that you have already
Eclipse
installed. For
details please
see
Eclipse Tutorial
.
Download the Android SDK from the Android homepage under
Android SDK download
. The download contains a zip file which you can extract to any
place
in
your file system, e.g. I placed it under
"c:\android-sdk-windows" .
In Eclipse open the Preferences dialog via Windows ->
Preferences. Select
Android and maintain the installation path of the
Android SDK.
Tip
If you maintain the location the Android plugin will remind you
frequently (and for every workspace). Join me in starring at
Bug 3210
to get this improved.
Select now Window -> Android SDK and AVD Manager from the menu.
Select available packages and select the latest version of the
SDK.
Press "Install selected" and confirm the license for all
package.
After the installation restart Eclipse.
You need to define a device which can be used for emulation.
Press the device manager button, press "New" and maintain the
following.
Press "Create AVD".This will create the device. To test if you
setup is correct, eelect your device and press
"Start".
After (a long time) your
device should be started.
Tip You can use the perspective "DDMS" to monitor your device.
Things are not always working as they should be. Several users report
that get the following errors:
-
Project ... is missing required source folder: 'gen'
-
The project could not be built until build path errors are
resolved.
-
Unable to open class file R.java.
To solve this error select from the menu Project -> Clean.
If you having problems with your own code you can use the LogCat
viewer as described in
LogCat Viewer
.
4. Your first Android project
Tip This app is also available on the Android Marketplace. Search
for "vogella" for find this example.
Select
File -> New -> Other -> Android -> Android Project and
create the Android project "de.vogella.android.temperature".
Maintain
the
following.
Press "Finish". This should create the following directory
structure.
"R.java" is a generated class which contains the text and the
UI
elements. Please do not try to modify this class manually.
The Android SDK allows to maintain certain artifacts, e.g.
strings and UI's, in two ways, via a rich editor and directly via
XML. The following description tries to use the rich UI but for
validation lists also the XML. You can switch between the two things
the the tab on the lower part of the screen. For example:
Modifying "string.xml" gives currently a NPE, for details see the
Bug report
. As a workaround you can select Window -> Preferences -> XML -> XML
Files -> Editor. Uncheck "Use inferred grammar in absence of
DTD/Schema".
Android allows to create attributes for resources, e.g. for
strings and / or colors. These attributes can be used in your UI
definition via XML or in your Java source code.
Select the file "res/values/string.xml" and press "Add".
Select
"Color" and maintain "myColor" as the name and "#3399CC" as
the
value.
Add also the following "String" attributes. String attributes
allow
to translate the application at a later point.
Table 1. String Attributes
Name | Value |
buttonHandler | myClickHandler |
celsius | to Celsius |
fahrenheit | to Fahrenheit |
Switch to the XML representation and validate that you
maintained the values correctly.
<?xml version="1.0" encoding="utf-8"?> <resources> <string name="hello">Hello World, Convert!</string> <string name="app_name">Temperature Converter</string> <color name="myColor">#3399CC</color> <string name="buttonHandler">myClickHandler</string> <string name="celsius">to Celsius</string> <string name="fahrenheit">to Fahrenheit</string> <string name="calc">Calculate</string> </resources>
Select "res/layout/main.xml" and open the Android editor via
double-click. This editor allows to maintain the UI via drag and drop
or directly via the XML source code. You can switch between both
representations via the tabs at the bottom of the editor. For
changing the postion and grouping elements you can use the outline
view.
Delete the "Hello World, Hello!" via a right mouse click. From
the "Views" bar, drag in
an "EditText". Add from the layout a
"RadioGroup" and then two RadioButtons, add one
"Button".
The result
should look like the
following and the corresponding XML is listed
below. Make sure that your code is the same as listed below.
Switch to "main.xml" and verify that your XML looks like the
following.
<?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">
<EditText android:text="@+id/EditText01" android:id="@+id/EditText01" android:layout_width="wrap_content" android:layout_height="wrap_content"></EditText> <RadioGroup android:id="@+id/RadioGroup01" android:layout_width="wrap_content" android:layout_height="wrap_content"> <RadioButton android:text="@+id/RadioButton01" android:id="@+id/RadioButton01" android:layout_width="wrap_content" android:layout_height="wrap_content"></RadioButton> <RadioButton android:text="@+id/RadioButton02" android:id="@+id/RadioButton02" android:layout_width="wrap_content" android:layout_height="wrap_content"></RadioButton> </RadioGroup> <Button android:text="@+id/Button01" android:id="@+id/Button01" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button> </LinearLayout>
4.5. Maintain UI properties
If you select a UI element you can change its properties via
the properties view. Select EditText and change the property "Layout
Width" to "fill_parent".
Assign the "celsius" string attribute to your "text" property
of the first radio button and "fahrenheit" to the second. Set the
property "Checked" to true for the first RadioButton. Assign
"calc" to
the text property of your button and assign "buttonHandler" to the
"onClick" property. Delete the text property
in the
EditText (this
means no text will be initially shown) and set
the
"Input type"
property to "numberSigned" and "number decimal".
Select the complete widget and use the
Properties view to set
the property
"background" to the color attribute "@color/myColor".
Switch to the "main.xml" tab and verify that the XML is
correctly maintained.
<?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:background="@color/myColor">
<EditText android:id="@+id/EditText01" android:layout_height="wrap_content" android:layout_width="fill_parent" android:inputType="numberSigned|numberDecimal"></EditText> <RadioGroup android:id="@+id/RadioGroup01" android:layout_width="wrap_content" android:layout_height="wrap_content"> <RadioButton android:id="@+id/RadioButton01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/celsius" android:checked="true"></RadioButton> <RadioButton android:id="@+id/RadioButton02" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/fahrenheit"></RadioButton> </RadioGroup> <Button android:id="@+id/Button01" android:layout_height="wrap_content" android:onClick="@string/buttonHandler" android:layout_width="wrap_content" android:text="@string/calc"></Button> </LinearLayout>
4.6. Code your applicatioin
Change your code in "Convert.java" to the following. Note that
the "myClickHandler" will be called basedon the "On Click" property
of your button.
package de.vogella.android.temperature;
import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.EditText; import android.widget.RadioButton; import android.widget.Toast;
public class Convert extends Activity { private EditText text;
@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); text = (EditText) findViewById(R.id.EditText01);
}
// This method is called at button click because we assigned the name to the // "On Click property" of the button public void myClickHandler(View view) { switch (view.getId()) { case R.id.Button01: RadioButton celsiusButton = (RadioButton) findViewById(R.id.RadioButton01); RadioButton fahrenheitButton = (RadioButton) findViewById(R.id.RadioButton02); if (text.getText().length() == 0) { Toast.makeText( this, "Please enter a valid number", Toast.LENGTH_LONG).show(); return; } float inputValue = Float.parseFloat(text.getText().toString()); if (celsiusButton.isChecked()) { text.setText(String .valueOf(convertFahrenheitToCelcius(inputValue))); } else { text.setText(String .valueOf(convertCelciusToFahrenheit(inputValue))); } // Switch to the other button if (fahrenheitButton.isChecked()) { fahrenheitButton.setChecked(false); celsiusButton.setChecked(true); } else { fahrenheitButton.setChecked(true); celsiusButton.setChecked(false); } break; } }
// Converts to celcius private float convertFahrenheitToCelcius(float fahrenheit) { return ((fahrenheit - 32) * 5 / 9); }
// Converts to fahrenheit private float convertCelciusToFahrenheit(float celsius) { return ((celsius * 9) / 5) + 32; } }
To start the Android Application, select your project, right
click on it, Run-As-> Android Application Be patient, the emulator
starts up very slow.
You should get the following result.
Type in a number, select your conversion and press the button.
The result should be displayed and the other option should get
selected.
4.8. Using the home menue
If you press the Home button you can also select your
application.
List can be used to display a scrollable list of items. You can
either use lists in your layout or if the purpose of your Activity is
to show primary a list you can extend ListActivities which provides
nice hocks for typical actions for lists.
5.2. Simple ListActivities
A ListActivity extends Activity and simplifies the approach to
show several objects in a list. It extends the
standard Activity with
a
standard ListView Elements, callbacks for
list events, e..g for
selecting a list element and helper methods to
access the current list
position and the selected element(s).
To test this create a new Android project
"de.vogella.android.listactivity" with the activity "MyList". You do
not need to change the default layout "main.xml". Create
the following
activity.
package de.vogella.android.listactivity;
import android.app.ListActivity; import android.os.Bundle; import android.view.View; import android.widget.ArrayAdapter; import android.widget.ListView; import android.widget.Toast;
public class MyList extends ListActivity {
/** Called when the activity is first created. */ public void onCreate(Bundle icicle) { super.onCreate(icicle); // Create an array of Strings, that will be put to our ListActivity String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse", "Ubuntu", "Solaris", "Android", "iPhone"}; // Create an ArrayAdapter, that will actually make the Strings above // appear in the ListView this.setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_checked, names)); }
@Override protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); // Get the item that was clicked Object o = this.getListAdapter().getItem(position); String keyword = o.toString(); Toast.makeText(this, "You selected: " + keyword, Toast.LENGTH_LONG) .show(); } }

5.3. ListActivities with own layout
The example above is boring, as only text is shown. You can
also define your own layout for the rows and assign this layout to
your row adapter. We will add a graphic to each list entry.
Create the following layout file
"rowlayout.xml" in the
res/layout folder of
your project "de.vogella.android.listactivity".
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content"> <ImageView android:id="@+id/icon" android:layout_height="wrap_content" android:src="@drawable/icon" android:layout_width="22px" android:layout_marginTop="4px" android:layout_marginRight="4px" android:layout_marginLeft="4px"> </ImageView> <TextView android:text="@+id/TextView01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/label" android:textSize="30px"></TextView> </LinearLayout>
Change your activity "MyList" to the following. This is
almost
the same coding as in the previous example, the only
difference is
that we are using our own layout in the ArrayAdapter
and telling the
adapter which UI element should contains the text.
package de.vogella.android.listactivity2;
import android.app.Activity; import android.app.ListActivity; import android.os.Bundle; import android.view.View; import android.widget.ArrayAdapter; import android.widget.ListView; import android.widget.Toast;
public class MyLayoutList extends ListActivity {
/** Called when the activity is first created. */ public void onCreate(Bundle icicle) { super.onCreate(icicle); // Create an array of Strings, that will be put to our ListActivity String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse", "Ubuntu", "Solaris", "Android", "iPhone" }; // Use your own layout and point the adapter to the UI elements which contains the label this.setListAdapter(new ArrayAdapter<String>(this, R.layout.rowlayout, R.id.label, names)); }
@Override protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); // Get the item that was clicked Object o = this.getListAdapter().getItem(position); String keyword = o.toString(); Toast.makeText(this, "You selected: " + keyword, Toast.LENGTH_LONG) .show();
} }

5.4. ListActivities with flexible layout
The above example uses one layout for all rows. If you want to
influence the display of the different rows you can also define your
own adapter and implement your own getView() method. This method is
responsible for creating the listview. In this method we will read
the pre-defined layout via LayoutInflator and return one individual
view per row.
Create the following class "MyArrayAdapter.java".
package de.vogella.android.listactivity;
import android.app.Activity; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ArrayAdapter; import android.widget.ImageView; import android.widget.TextView;
public class MyArrayAdapter extends ArrayAdapter<String> { private final Activity context; private final String[] names;
public MyArrayAdapter(Activity context, String[] names) { super(context, R.layout.rowlayout, names); this.context = context; this.names = names; }
@Override public View getView(int position, View convertView, ViewGroup parent) { LayoutInflater inflater = context.getLayoutInflater(); View rowView = inflater.inflate(R.layout.rowlayout, null, true); TextView label = (TextView) rowView.findViewById(R.id.label); label.setText(names[position]); System.out.println(names[position]); // Change the icon for Windows and iPhone if (names[position].startsWith("Windows7") || names[position].startsWith("iPhone") ) { ImageView imageView = (ImageView) rowView.findViewById(R.id.icon); imageView.setImageResource(R.drawable.alt_window_16); } return rowView; }
}
package de.vogella.android.listactivity;
import android.app.ListActivity; import android.os.Bundle; import android.view.View; import android.widget.ListView; import android.widget.Toast;
public class MyList extends ListActivity {
/** Called when the activity is first created. */ public void onCreate(Bundle icicle) { super.onCreate(icicle); // Create an array of Strings, that will be put to our ListActivity String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse", "Ubuntu", "Solaris", "Android", "iPhone"}; this.setListAdapter(new MyArrayAdapter(this, names)); }
@Override protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); // Get the item that was clicked Object o = this.getListAdapter().getItem(position); String keyword = o.toString(); Toast.makeText(this, "You selected: " + keyword, Toast.LENGTH_LONG) .show(); } }
6. Menu, Preferences and Intents
This chapter will demonstrate how to create and evaluate a menu,
how
to define preferences and how to navigate between activities via
an
intent
.
Create a project "de.vogella.android.preferences" with the
activity
"HelloPreferences". Change the UI in the file
"/res/layout/main.xml" to the following:
<?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:id="@+id/Button01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Show Preferences"></Button> </LinearLayout>
Menus can be defined via XML files. Select your project, right
click
on it and
select New -> Other ->
Android -> "Android XML File".
Press Add and select "Item". Maintain the following value. This
defines the entries in your menu. We will have only one entry.
Change your class "HelloPreferences" to the following. The
OnCreateOptionsMenu method is used to create the menu. Please note
that at the moment nothing happens if you select this menu. The
behavior will be later implemented in the method
"onOptionsItemSelected".
package de.vogella.android.preferences;
import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuInflater;
public class HelloPreferences extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.menu, menu); return true; } }
Run your application and press "Menu" on the emulator.
Your menu
should be
displayed.
Preference values can also be stored as a XML resource. Create
another Android XML File "preferences.xml" this time of type
preferences.
Press Add, add a category and add two preferences
"EditTextPreferences" to this category : "User" and
"Password".
Create the class "Preferences" which will load the
"preference.xml".
package de.vogella.android.preferences;
import android.os.Bundle; import android.preference.PreferenceActivity;
public class Preferences extends PreferenceActivity {
/** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.preferences); }
}
Select "AndroidManifest.xml" and the tab "Application". Add the
activity "Preferences".
To use the preferences add a button to your main.xml with the
id
"@+id/Button01" and change the coding of HelloPreferences to the
following.
package de.vogella.android.preferences;
import android.app.Activity; import android.content.Intent; import android.content.SharedPreferences; import android.os.Bundle; import android.preference.PreferenceManager; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.Toast;
public class HelloPreferences extends Activity { SharedPreferences preferences;
/** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button button = (Button) findViewById(R.id.Button01); // Initialize preferences preferences = PreferenceManager.getDefaultSharedPreferences(this); button.setOnClickListener(new OnClickListener() {
@Override public void onClick(View v) { String username = preferences.getString("username", "n/a"); String password = preferences.getString("password", "n/a"); Toast.makeText(HelloPreferences.this, "You maintained user: " + username + " and password: " + password, Toast.LENGTH_LONG).show();
} }); }
@Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.menu, menu); return true; }
// This method is called once the menu is selected @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { // We have only one menu option case R.id.preferences: // Launch Preference activity Intent i = new Intent(HelloPreferences.this, Preferences.class); startActivity(i); // A toast is a view containing a quick little message for the user. Toast.makeText(HelloPreferences.this, "Here you can maintain your user credentials.", Toast.LENGTH_LONG).show(); break;
} return true; } }
Run your application. Press the "menu" hardware button and then
select your menu item "Preferences". You should be able to enter your
user settings then press the back hardware button to return to your
main activity and press the button. The saved
values should be
displayed in a small message windows (Toast).
ContentProvider are used to provide data from an application to
another. ContentProvider do not store the data but provide the
interface for other applications to access the data.
The following example will use an existing context provider
from "Contacts".
7.2. Create contacts on your emulator
Select the home menu and then the menu entry "Contacts" to
create contacts.
Press Menu and select "New Contact".
As a result you should have a few new contacts.
Create a new Android project
"de.vogella.android.contentprovider" with the activity
"ContactsView".
Rename the id of the the existing TextView from the example
wizard to "contactview". Delete the default text. Also change the
layout_height to
"fill_parent".
The resulting main.xml should look like the following.
<?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="fill_parent" android:id="@+id/contactview" /> </LinearLayout>
In AndroidManifest.xml add the User Permission that the
application can use "android.permission.READ_CONTACTS".
Change the coding of the activity.
package de.vogella.android.contentprovider;
import android.app.Activity; import android.database.Cursor; import android.net.Uri; import android.os.Bundle; import android.provider.ContactsContract; import android.widget.TextView;
public class ContactsView extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TextView contactView = (TextView) findViewById(R.id.contactview);
Cursor cursor = getContacts();
while (cursor.moveToNext()) {
String displayName = cursor.getString(cursor .getColumnIndex(ContactsContract.Data.DISPLAY_NAME)); contactView.append("Name: "); contactView.append(displayName); contactView.append("\n"); } }
private Cursor getContacts() { // Run query Uri uri = ContactsContract.Contacts.CONTENT_URI; String[] projection = new String[] { ContactsContract.Contacts._ID, ContactsContract.Contacts.DISPLAY_NAME }; String selection = ContactsContract.Contacts.IN_VISIBLE_GROUP + " = '" + ("1") + "'"; String[] selectionArgs = null; String sortOrder = ContactsContract.Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC";
return managedQuery(uri, projection, selection, selectionArgs, sortOrder); }
}
ScrollViews can be used to contain one child that might be to
big to fit on one screen. If the child is to big the ScrollView will
display a scroll bar to scroll the context. Of course the child can be
a layout which can then contain other elements.
Create an android project "de.vogella.android.scrollview" with
the activity "ScrollView". Create the following layout and class.
<?xml version="1.0" encoding="utf-8"?> <ScrollView xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:fillViewport="true">
<LinearLayout android:id="@+id/LinearLayout01" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="wrap_content"> <TextView android:id="@+id/TextView01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="This is a header" android:textAppearance="?android:attr/textAppearanceLarge" android:paddingLeft="8dip" android:paddingRight="8dip" android:paddingTop="8dip"></TextView> <TextView android:text="@+id/TextView02" android:id="@+id/TextView02" android:layout_width="wrap_content" android:layout_height="fill_parent" android:layout_weight="1.0"></TextView> <LinearLayout android:id="@+id/LinearLayout02" android:layout_width="wrap_content" android:layout_height="wrap_content"> <Button android:id="@+id/Button01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Submit" android:layout_weight="1.0"></Button> <Button android:id="@+id/Button02" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Cancel" android:layout_weight="1.0"></Button> </LinearLayout> </LinearLayout> </ScrollView>
package de.vogella.android.scrollview;
import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.TextView;
public class ScrollView extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TextView view = (TextView) findViewById(R.id.TextView02); String s=""; for (int i=0; i < 100; i++) { s += "vogella.de "; } view.setText(s); } }
The attribute "android:fillViewport="true"" ensures that the the
scrollview is set to the full screen even if the elements are smaller
then one screen and the "layout_weight" tell the android system that
these elements should be extended.
9. Services and Broadcast Receiver
The Android platform provides a lot of pre-defined services,
usually exposed via a Manager class. In this chapter we will use the
AlertManager and VibratorManager. The alarm manager will in our
example our own broadcast receiver.
Create a new project "de.vogella.android.alarm" with the
activity "AlarmActivity". Create the following layout.
<?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">
<EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/time" android:hint="Number of seconds" android:inputType="numberDecimal"></EditText><Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/ok" android:onClick="startAlert" android:text="Start Counter"></Button>
</LinearLayout>
Create the following broadcast receiver class. This class will
get the Vibrator service.
package de.vogella.android.alarm;
import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.os.Vibrator; import android.widget.Toast;
public class MyBroadcastReceiver extends BroadcastReceiver { @Override public void onReceive(Context context, Intent intent) { Toast.makeText(context, "Don't panik but your time is up!!!!.", Toast.LENGTH_LONG).show(); // Vibrate the mobile phone Vibrator vibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE); vibrator.vibrate(2000); }
}
Maintain this class as broadcast receiver in
"AndroidManifest.mf" and allow the vibrate authorization.
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="de.vogella.android.alarm" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".AlarmActivity" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <receiver android:name=".MyBroadcastReceiver" android:enabled="true"> </receiver> </application> <uses-sdk android:minSdkVersion="8" />
<uses-permission android:name="android.permission.VIBRATE"></uses-permission> </manifest>
Now define your main Activitiy. This activity will create an
Intent for the Broadcast receiver and get the AlarmManager service.
package de.vogella.android.alarm;
import android.app.Activity; import android.app.AlarmManager; import android.app.PendingIntent; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.widget.EditText; import android.widget.Toast;
public class AlarmActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); }
public void startAlert(View view) { EditText text = (EditText) findViewById(R.id.time); int i = Integer.parseInt(text.getText().toString()); Intent intent = new Intent(this, MyBroadcastReceiver.class); PendingIntent pendingIntent = PendingIntent.getBroadcast( this.getApplicationContext(), 234324243, intent, 0); AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE); alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (i * 1000), pendingIntent); Toast.makeText(this, "Alarm set in " + i + " seconds", Toast.LENGTH_LONG).show(); }
}
You can see the log (including System.out.print() statements)
via the
LogCat view.
The file explorer allows to see the files on the android
simulator.
11.1. Android Debugging Bridge - Shell
You can access your Android emulator also via the console. Open
a
shell, switch to your "android-sdk" installation directory into the
folder "tools". Start the shell via the following command "adb
shell".
adb shell
This
will connect you to your device and give you
Linux command line
access
to the underlying file system, e.g. ls, rm, mkdir, etc. The
application data is stored in the directory
"/data/data/package_of_your_app".
If you have several devices running you can issue commands to
one individuel device.
# Lists all devices adb devices #Result List of devices attached emulator-5554 attached emulator-5555 attached # Issue a command to a specific device adb -s emulator-5554 shell
11.2. Uninstall an application via adb
You can uninstall an android application via the shell. Switch
the the data/app directory (cd /data/app) and simply delete your
android application.
11.3. Emulator Console via telnet
Alternatively to adb you can also use telnet to connect to the
device. This allows you to simulate certain things, e.g. incoming
call, change the network "stability", set your current geocodes, etc.
Use "telnet localhost 5554" to conntect to your simulated
device. To
exit the console session, use the command "quit" or
"exit".
For example to change the power settings of your phone, to
receive an sms and to get an incoming call make the following.
# connects to device telnet localhost 5554 # set the power level power status full power status charging # make a call to the device gsm call 012041293123 # send a sms to the device sms send 12345 Will be home soon # set the geo location
For more information on the emulator console please see
Emulator Console manual
12. Deploy your application on a real device
Turn on "USB Debugging" on your device in the settings. Select in the
settings Applications > Development, then enable USB
debugging. You
also need to install the driver for your mobile phone. For details
please see
Developing on a Device
. Please note that the Android version you are developing for must be
the installed version on your phone.
To select your phone, select the "Run Configurations", select
"Manual" selection and select your device.
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