In last article, Using color in Android, by XML, described how to define color in XML file. Here, changing color using Java code will be described.



Keep using the main.xml and mycolor.xml

Modify Java code

package com.exercise.AndroidColor;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;

public class AndroidColor extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
      
       final LinearLayout backGround = (LinearLayout)findViewById(R.id.background);
       Button whiteButton = (Button)findViewById(R.id.whitebutton);
       Button redButton = (Button)findViewById(R.id.redbutton);
       Button greenButton = (Button)findViewById(R.id.greenbutton);
       Button blueButton = (Button)findViewById(R.id.bluebutton);
      
       whiteButton.setOnClickListener(new Button.OnClickListener(){
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    backGround.setBackgroundResource(android.R.color.white);
   }});
      
       redButton.setOnClickListener(new Button.OnClickListener(){
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    backGround.setBackgroundColor(0xff000000 + 0xff0000);
   }});
      
       greenButton.setOnClickListener(new Button.OnClickListener(){
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    backGround.setBackgroundResource(R.color.green);
   }});
      
       blueButton.setOnClickListener(new Button.OnClickListener(){
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    backGround.setBackgroundResource(R.color.blue);
   }});
   }
}

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To generate random number in Android, class java.util.Random can be used.

This class java.util.Random provides methods that generates pseudo-random numbers of different types, such as int, long, double, and float.

It support two public constructor:
Random() - Construct a random generator with the current time of day in milliseconds as the initial state.
Random(long seed) - Construct a random generator with the given seed as the initial state.



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"
   >
<TextView 
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="@string/hello"
   />
<Button
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Generate Random number"
   android:id="@+id/generate"
 />
<TextView
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:id="@+id/generatenumber"
 />
</LinearLayout>

package com.exercise.AndroidRandom;

import java.util.Random;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class AndroidRandom extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
      
       final Random myRandom = new Random();
      
       Button buttonGenerate = (Button)findViewById(R.id.generate);
       final TextView textGenerateNumber = (TextView)findViewById(R.id.generatenumber);
      
       buttonGenerate.setOnClickListener(new OnClickListener(){

   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    textGenerateNumber.setText(String.valueOf(myRandom.nextInt()));
   }});
   }
}

XmlResourceParser is the XML parsing interface returned for an XML resource. This is a standard XmlPullParser interface, as well as an extended AttributeSet interface and an additional close() method on this interface for the client to indicate when it is done reading the resource.

In this exercise, we read our own XML Resource (in /res/xml folder) using XmlResourceParser, and display the contents on screen.



First of all, create a folder /res/xml, and our own XML file myxml.xml

<?xml version="1.0" encoding="utf-8"?>
<rootelement1>
<subelement>
 Hello XML Sub-Element 1
</subelement>
<subelement>
 Hello XML Sub-Element 2
 <subsubelement>Sub Sub Element</subsubelement>
</subelement>
</rootelement1>

<?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"
  />
<TextView
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:id="@+id/my_xml"
  />
</LinearLayout>

package com.exercise.AndroidXmlResource;

import java.io.IOException;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;

import android.app.Activity;
import android.content.res.Resources;
import android.content.res.XmlResourceParser;
import android.os.Bundle;
import android.widget.TextView;

public class AndroidXmlResource extends Activity {
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
    
      TextView myXmlContent = (TextView)findViewById(R.id.my_xml);
      String stringXmlContent;
 try {
  stringXmlContent = getEventsFromAnXML(this);
  myXmlContent.setText(stringXmlContent);
 } catch (XmlPullParserException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } catch (IOException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 }
  }

  private String getEventsFromAnXML(Activity activity)
  throws XmlPullParserException, IOException
  {
   StringBuffer stringBuffer = new StringBuffer();
   Resources res = activity.getResources();
   XmlResourceParser xpp = res.getXml(R.xml.myxml);
   xpp.next();
   int eventType = xpp.getEventType();
   while (eventType != XmlPullParser.END_DOCUMENT)
   {
    if(eventType == XmlPullParser.START_DOCUMENT)
    {
     stringBuffer.append("--- Start XML ---");
    }
    else if(eventType == XmlPullParser.START_TAG)
    {
     stringBuffer.append("\nSTART_TAG: "+xpp.getName());
    }
    else if(eventType == XmlPullParser.END_TAG)
    {
     stringBuffer.append("\nEND_TAG: "+xpp.getName());
    }
    else if(eventType == XmlPullParser.TEXT)
    {
     stringBuffer.append("\nTEXT: "+xpp.getText());
    }
    eventType = xpp.next();
   }
   stringBuffer.append("\n--- End XML ---");
   return stringBuffer.toString();
  }
}

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In the last article, "Read XML Resources in Android, using XmlResourceParser: XML parsing interface", Android application read XML resource inside application. In the current article, a external XML will be read using Android SAX APIs.

The source of XML is "http://feeds.feedburner.com/Android-er?format=xml", which is RSS feed of my blog.

SAX is the Simple API for XML, originally a Java-only API. SAX was the first widely adopted API for XML in Java, and is a “de facto” standard. The current version is SAX 2.0.1, and there are versions for several programming language environments other than Java.

org.xml.sax is a Android's package provides the core SAX APIs.

In order to make it simple, only the contents under "title" tag will be retrieved and appended as a string.



To allow the Android application, "android.permission.INTERNET" have to be granted to the application. Modify AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.exercise.AndroidRssReader"
    android:versionCode="1"
    android:versionName="1.0">
  <application android:icon="@drawable/icon" android:label="@string/app_name">
      <activity android:name=".AndroidRssReader"
                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" />
<uses-permission android:name="android.permission.INTERNET" />
</manifest>

<?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" />
<ScrollView
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<TextView
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:id="@+id/result" />
</ScrollView>
</LinearLayout>

package com.exercise.AndroidRssReader;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class AndroidRssReader extends Activity {

String streamTitle = "";

  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
    
      TextView result = (TextView)findViewById(R.id.result);
    
      try {
  URL rssUrl = new URL("http://feeds.feedburner.com/Android-er?format=xml");
  SAXParserFactory mySAXParserFactory = SAXParserFactory.newInstance();
  SAXParser mySAXParser = mySAXParserFactory.newSAXParser();
  XMLReader myXMLReader = mySAXParser.getXMLReader();
  RSSHandler myRSSHandler = new RSSHandler();
  myXMLReader.setContentHandler(myRSSHandler);
  InputSource myInputSource = new InputSource(rssUrl.openStream());
  myXMLReader.parse(myInputSource);
 
  result.setText(streamTitle);
 
 } catch (MalformedURLException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  result.setText("Cannot connect RSS!");
 } catch (ParserConfigurationException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  result.setText("Cannot connect RSS!");
 } catch (SAXException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  result.setText("Cannot connect RSS!");
 } catch (IOException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  result.setText("Cannot connect RSS!");
 }
    
    
  }

  private class RSSHandler extends DefaultHandler
  {
   final int stateUnknown = 0;
   final int stateTitle = 1;
   int state = stateUnknown;
  
   int numberOfTitle = 0;
   String strTitle = "";
   String strElement = "";
  
 @Override
 public void startDocument() throws SAXException {
  // TODO Auto-generated method stub
  strTitle = "--- Start Document ---\n";
 }

 @Override
 public void endDocument() throws SAXException {
  // TODO Auto-generated method stub
  strTitle += "--- End Document ---";
  streamTitle = "Number Of Title: " + String.valueOf(numberOfTitle) + "\n"
     + strTitle;
 }

 @Override
 public void startElement(String uri, String localName, String qName,
   Attributes attributes) throws SAXException {
  // TODO Auto-generated method stub
  if (localName.equalsIgnoreCase("title"))
  {
   state = stateTitle;
   strElement = "Title: ";
   numberOfTitle++;
  }
  else
  {
   state = stateUnknown;
  }
 }

 @Override
 public void endElement(String uri, String localName, String qName)
   throws SAXException {
  // TODO Auto-generated method stub
  if (localName.equalsIgnoreCase("title"))
  {
   strTitle += strElement + "\n";
  }
  state = stateUnknown;
 }

 @Override
 public void characters(char[] ch, int start, int length)
   throws SAXException {
  // TODO Auto-generated method stub
  String strCharacters = new String(ch, start, length);
  if (state == stateTitle)
  {
   strElement += strCharacters;
  }
 }
  
  }
}

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It's very easy to add a Analog Clock in Android, Just add the code of AnalogClock in main.xml.



AnalogClock is a widget to display an analogic clock with two hands for hours and minutes.

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"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<AnalogClock
    android:id="@+id/myAnalogClock"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    />

</LinearLayout>

It's another exercise to read Android system information, using system provided method getProperty.



Create a new Android Application, with the Activity named AndroidSYSinfoActivity. Modify the main.xml and AndroidSYSinfoActivity.java:
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"
 >
<TextView
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:gravity="center_horizontal"
 android:text="android-er.blogspot.com"
 android:autoLink="web"
 />
<TextView
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="Android System:"
 />
<TextView
 android:id="@+id/SYSinfo"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 />
</LinearLayout>

package com.exercise.AndroidSYSinfo;

import com.exercise.AndroidSYSinfo.R;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class AndroidSYSinfoActivity extends Activity {
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.main);
  
  
     TextView SYSinfo = (TextView) findViewById(R.id.SYSinfo);
     SYSinfo.setText(ReadSYSinfo());
 }

 private static StringBuffer SYSinfoBuffer;

 private String ReadSYSinfo()
 {
  SYSinfoBuffer = new StringBuffer();
  
  getProperty("os.name", "os.name", SYSinfoBuffer);
  getProperty("os.version", "os.version", SYSinfoBuffer);
  
  getProperty("java.vendor.url", "java.vendor.url", SYSinfoBuffer);
  getProperty("java.version", "java.version", SYSinfoBuffer);
  getProperty("java.class.path", "java.class.path", SYSinfoBuffer);
  getProperty("java.class.version", "java.class.version", SYSinfoBuffer);
  getProperty("java.vendor", "java.vendor", SYSinfoBuffer);
  getProperty("java.home", "java.home", SYSinfoBuffer);
  
  getProperty("user.name", "user.name", SYSinfoBuffer);
  getProperty("user.home", "user.home", SYSinfoBuffer);
  getProperty("user.dir", "user.dir", SYSinfoBuffer);
  
  return SYSinfoBuffer.toString();
 }

 private void getProperty(String desc, String property, StringBuffer tBuffer)
 {
  tBuffer.append(desc);
  tBuffer.append(" : ");
  tBuffer.append(System.getProperty(property));
  tBuffer.append("\n");
 }
}