xml android

XML stands for Extensible Mark-up Language.XML is a very popular format and commonly used for sharing data on the internet. This chapter explains how to parse the XML file and extract necessary information from it.

Android provides three types of XML parsers which are DOM,SAX and XMLPullParser. Among all of them android recommend XMLPullParser because it is efficient and easy to use. So we are going to use XMLPullParser for parsing XML

The first step is to identify the fields in the XML data in which you are interested in. For example. In the XML given below we interested in getting temperature only.

<?xml version="1.0"?>

<current>

<city id="2643743" name="London">

<coord lon="-0.12574" lat="51.50853"/>

<country>GB</country>

<sun rise="2013-10-08T06:13:56" set="2013-10-08T17:21:45"/>

</city>

<temperature value="289.54" min="289.15" max="290.15" unit="kelvin"/>

<humidity value="77" unit="%"/>

<pressure value="1025" unit="hPa"/>

</country>

XML - Elements

An xml file consist of many components. Here is the table defining the components of an XML file and their description.

Sr.No Component & description

1 Prolog

An XML file starts with a prolog. The first line that contains the information about a file is prolog

2 Events

An XML file has many events. Event could be like this. Document starts , Document ends, Tag start , Tag end and Text e.t.c

3 Text

Apart from tags and events, and xml file also contains simple text. Such as GB is a text in the country tag.

4 Attributes

Attributes are the additional properties of a tag such as value e.t.c

XML - Parsing

In the next step, we will create XMLPullParser object , but in order to create that we will first create XmlPullParserFactory object and then call its newPullParser() method to create XMLPullParser. Its syntax is given below −

private XmlPullParserFactory xmlFactoryObject = XmlPullParserFactory.newInstance();

private XmlPullParser myparser = xmlFactoryObject.newPullParser();

The next step involves specifying the file for XmlPullParser that contains XML. It could be a file or could be a Stream. In our case it is a stream.Its syntax is given below −

myparser.setInput(stream, null);

The last step is to parse the XML. An XML file consist of events, Name, Text, AttributesValue e.t.c. So XMLPullParser has a separate function for parsing each of the component of XML file. Its syntax is given below −

int event = myParser.getEventType();

while (event != XmlPullParser.END_DOCUMENT)

{

String name=myParser.getName();

switch (event){

case XmlPullParser.START_TAG:

break;

case XmlPullParser.END_TAG:

if(name.equals("temperature")){

temperature = myParser.getAttributeValue(null,"value");

}

break;

}

event = myParser.next();

}

The method getEventType returns the type of event that happens. e.g: Document start , tag start e.t.c. The method getName returns the name of the tag and since we are only interested in temperature , so we just check in conditional statement that if we got a temperature tag , we call the method getAttributeValue to return us the value of temperature tag.

Apart from the these methods, there are other methods provided by this class for better parsing XML files. These methods are listed below −

Sr.No Method & description

1 getAttributeCount()

This method just Returns the number of attributes of the current start tag

2 getAttributeName(int index)

This method returns the name of the attribute specified by the index value

3 getColumnNumber()

This method returns the Returns the current column number, starting from 0.

4 getDepth()

This method returns Returns the current depth of the element.

5 getLineNumber()

Returns the current line number, starting from 1.

6 getNamespace()

This method returns the name space URI of the current element.

7 getPrefix()

This method returns the prefix of the current element

8 getName()

This method returns the name of the tag

9 getText()

This method returns the text for that particular element

10 isWhitespace()

This method checks whether the current TEXT event contains only whitespace characters.

Example

Here is an example demonstrating the use of XMLPullParser class. It creates a basic Weather application that allows you to parse XML from google weather api and show the result.

To experiment with this example, you can run this on an actual device or in an emulator.

Steps Description

1 You will use Android studio to create an Android application under a package com.example.sairamkrishna.myapplication. While creating this project, make sure you Target SDK and Compile With at the latest version of Android SDK to use higher levels of APIs.

2 Modify src/MainActivity.java file to add necessary code.

3 Modify the res/layout/activity_main to add respective XML components

4 Create a new java file under src/HandleXML.java to fetch and parse XML data

5 Modify AndroidManifest.xml to add necessary internet permission

6 Run the application and choose a running android device and install the application on it and verify the results

Following is the content of the modified main activity file MainActivity.java.

package com.example.sairamkrishna.myapplication;

import android.content.Context;

import android.content.Intent;

import android.content.SharedPreferences;

import android.graphics.Typeface;

import android.support.v7.app.ActionBarActivity;

import android.os.Bundle;

import android.view.Menu;

import android.view.MenuItem;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

import android.widget.Toast;

com.example.sairamkrishna.myapplication

public class MainActivity extends ActionBarActivity {

EditText ed1,ed2,ed3,ed4,ed5;

private String url1 = "http://api.openweathermap.org/data/2.5/weather?q=";

private String url2 = "&mode=xml";

private HandleXML obj;

Button b1;

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

b1=(Button)findViewById(R.id.button);

ed1=(EditText)findViewById(R.id.editText);

ed2=(EditText)findViewById(R.id.editText2);




b1.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

String url = ed1.getText().toString();

String finalUrl = url1 + url + url2;

ed2.setText(finalUrl);

obj = new HandleXML(finalUrl);

obj.fetchXML();

while(obj.parsingComplete);

ed2.setText(obj.getCountry());

ed3.setText(obj.getTemperature());

ed4.setText(obj.getHumidity());

ed5.setText(obj.getPressure());

}

});

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.menu_main, menu);

return true;

}

@Override

public boolean onOptionsItemSelected(MenuItem item) {

// Handle action bar item clicks here. The action bar will

// automatically handle clicks on the Home/Up button, so long

// as you specify a parent activity in AndroidManifest.xml.

int id = item.getItemId();

//noinspection SimplifiableIfStatement

if (id == R.id.action_settings) {

return true;

}

return super.onOptionsItemSelected(item);

}

}

Following is the content of src/com.example.xmlparser/HandleXML.java.

package com.example.sairamkrishna.myapplication;

import org.xmlpull.v1.XmlPullParser;

import org.xmlpull.v1.XmlPullParserFactory;

import java.io.InputStream;

import java.net.HttpURLConnection;

import java.net.URL;

/**

* Created by Sairamkrishna on 4/11/2015.

*/

public class HandleXML {

private String country = "county";

private String temperature = "temperature";

private String humidity = "humidity";

private String pressure = "pressure";

private String urlString = null;

private XmlPullParserFactory xmlFactoryObject;

public volatile boolean parsingComplete = true;

public HandleXML(String url){

this.urlString = url;

}

public String getCountry(){

return country;

}

public String getTemperature(){

return temperature;

}

public String getHumidity(){

return humidity;

}

public String getPressure(){

return pressure;

}

public void parseXMLAndStoreIt(XmlPullParser myParser) {

int event;

String text=null;

try {

event = myParser.getEventType();

while (event != XmlPullParser.END_DOCUMENT) {

String name=myParser.getName();

switch (event){

case XmlPullParser.START_TAG:

break;

case XmlPullParser.TEXT:

text = myParser.getText();

break;

case XmlPullParser.END_TAG:

if(name.equals("country")){

country = text;

}

else if(name.equals("humidity")){

humidity = myParser.getAttributeValue(null,"value");

}

else if(name.equals("pressure")){

pressure = myParser.getAttributeValue(null,"value");

}

else if(name.equals("temperature")){

temperature = myParser.getAttributeValue(null,"value");

}

else{

}

break;

}

event = myParser.next();

}

parsingComplete = false;

}

catch (Exception e) {

e.printStackTrace();

}

}

public void fetchXML(){

Thread thread = new Thread(new Runnable(){

@Override

public void run() {

try {

URL url = new URL(urlString);

HttpURLConnection conn = (HttpURLConnection)url.openConnection();

conn.setReadTimeout(10000 /* milliseconds */);

conn.setConnectTimeout(15000 /* milliseconds */);

conn.setRequestMethod("GET");

conn.setDoInput(true);

conn.connect();

InputStream stream = conn.getInputStream();

xmlFactoryObject = XmlPullParserFactory.newInstance();

XmlPullParser myparser = xmlFactoryObject.newPullParser();

myparser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES, false);

myparser.setInput(stream, null);

parseXMLAndStoreIt(myparser);

stream.close();

}

catch (Exception e) {

e.printStackTrace();

}

}

});

thread.start();

}

}

Following is the modified content of the xml res/layout/activity_main.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" android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="XML Fetch"

android:id="@+id/textView"

android:layout_alignParentTop="true"

android:layout_centerHorizontal="true"

android:textSize="30dp" />

<TextView



android:text="Tutorials Point"

android:id="@+id/textView2"

android:layout_below="@+id/textView"

android:layout_centerHorizontal="true"

android:textSize="35dp"

android:textColor="#ff16ff01" />

<EditText



android:id="@+id/editText"

android:hint="Location"

android:layout_below="@+id/textView2"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:layout_marginTop="61dp"

android:layout_alignParentRight="true"

android:layout_alignParentEnd="true" />

<Button



android:text="Weather "

android:id="@+id/button"

android:layout_below="@+id/editText"

android:layout_centerHorizontal="true" />

<EditText



android:id="@+id/editText2"

android:layout_below="@+id/button"



android:layout_alignRight="@+id/editText"

android:layout_alignEnd="@+id/editText"

android:text="Currency" />

<EditText




android:layout_below="@+id/editText2"




android:layout_alignParentEnd="true"

android:text="Temp" />

<EditText







android:layout_alignRight="@+id/editText3"

android:layout_alignEnd="@+id/editText3"

android:text="Humidity" />

<EditText








android:layout_alignParentEnd="true"

android:text="Pressure" />

</RelativeLayout>

Following is the content of AndroidManifest.xml file.

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="com.example.sairamkrishna.myapplication" >

<uses-permission android:name="android.permission.INTERNET"/>

<application

android:allowBackup="true"

android:icon="@mipmap/ic_launcher"

android:label="@string/app_name"

android:theme="@style/AppTheme" >

<activity

android:name=".MainActivity"

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>

</manifest>

Let's try to run our application we just modified. I assume you had created your AVD while doing environment setup. To run the app from Android studio, open one of your project's activity files and click Run Eclipse Run Icon icon from the toolbar. Android studio installs the app on your AVD and starts it and if everything is fine with your setup and application, it will display following Emulator window −

Anroid XML Parser Tutorial

Now what you need to do is to enter any location in the location field. For example , i have entered india. Press the weather button , when you enter the location. The following screen would appear in you AVD −

Anroid XML Parser Tutorial

Now when you press the weather button, the application will contact the Google Weather API and will request for your necessary XML location file and will parse it. In case of London following file would be returned −

Anroid XMLParser Tutorial

Note that this temperature is in kelvin, so if you want to convert it into more understandble format , you have to convert it into Celcius.

Creating a User Interface using XML

Prerequisites

Before starting with this tutorial you should have read “Android SDK and Eclipse IDE”, or some other

“Hello World” like tutorial on Android. If you use a computer at Campus Haninge, read appendix A in

the tutorial mentioned above.

Although you can find a project with the solution to this exercise at Bilda, the best way to learn the

basics on creating user interfaces in Android is to do it yourself, using the tools in Eclipse as described

in the text.

Introduction

When developing an Android application you should define the components and their properties in

your user interface using XML. Although you can define the components in the source code, it’s good

practice to separate this from the rest of the code (the code dealing with the applications event

handling and logic).

In this exercise you will define a simple user interface in XML, using the layout editor in Eclipse. The

goal is a user interface, UI, like the one below.

Create a project

Create a new Android project with the following properties:

Project name, TemperatureConverter

Build target, Android 2.1

Application Name, Temperature Converter

Package Name, se.kth.temperature

Create Activity, TemperatureActivity

Min SDK version, 7

Building the UI using the XML editor in Eclipse

Open the file res/layout/main.xml. This is where the layout of your (main) UI is defined. Use the tabs

at the bottom to switch between the Graphical layout and the XML code defining the layout.‐The UI contains a LinearLayout with a TextView presenting a text (@string/hello is defined in

res/values/string.xml).

Switch to XML (the tab main.xml at the bottom of the panel). It should look like this:


<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:text="@string/hello"

/>

</LinearLayout>

Switch back to graphical layout and remove the TextView; right click it and select delete. Switch to‐XML view again and check that the TextView is removed.‐Adding Views

Remember, in an Android, a View can be an atomic UI component, a Button, TextView or such, or it

can be a container, ViewGroup, for example a layout component.

Let’s add some view components in our LinerLayout. Switch to graphical layout.

First add a TextView for text input; click on EditText in the right panel, then drag and drop the

component onto the layout.

Managing View properties

To manage the properties for this EditText, right click the component and select‐

Show In…/Properties. A new tab, Properties, is opened below the graphical layout. Here, you can set

properties for the EditText.

For example, to change the text size, browse to the corresponding line and set the value “16sp”

(scaled pixels).

Also set/change these properties for the EditText component:

Hint Input a temperature Text displayed when input is empty

Id @+id/TextInput This is the id used when referencing this view from

your source code. Must begin with “@+id/”

Input type numberDecimal This allows only decimal number input

Lines 1 Single line

Text The displayed texts, in this case none.

Text size 16sp Must have a unit, sp = scale-independent pixels.

Layout width fill_parent Use the drop down menu to browse the alternatives

Your XML file should contain this information (though the line breaks and the indentation might be‐different in your version):






>

<EditText


android:textSize="16sp"

android:lines="1"

android:id="@+id/TextInput"


android:hint="Input a temperature"

android:inputType="numberDecimal"

>

</EditText>

</LinearLayout>

Adding more views

In the same way as described above, add the following using drag and drop.

• A RadioGroup (a layout)

• In the RadioGroup, two RadioButtons. Make sure you drop them inside the RadioGroup

(check the xml code)‐• A button

• A TextView (for the output)

For the RadioButtons, set the Id, Text and Text size properties to

“@+id/CelciusButton“,“To Fahrenheit”, “16sp” and “@+id/FahrenheitButton“, “To Celcius” , “16 sp”

respectively.

Set the same properties for the Button to “@+id/CalculateButton“,“Calculate” and “16sp”

respectively.

For the TextView, set “@+id/TextOutput“,“” and “16sp”.

The XML code should, more or less, look like below. Make sure the RadioButtons are defined inside‐the RadioGroup.






>

<EditText



android:lines="1"

android:id="@+id/TextInput"


android:hint="Input a temperature"

android:inputType="numberDecimal"

>

</EditText>

<RadioGroup

android:id="@+id/RadioGroup01"



>

<RadioButton




android:text="To Celcius"

android:id="@+id/CelciusButton"

>

</RadioButton>

<RadioButton



android:id="@+id/FahrenheitButton"

android:text="To Fahrenheit"


>

</RadioButton>

</RadioGroup>

<Button




android:text="Calculate"

android:id="@+id/CalculateButton"

>

</Button>

<TextView



android:id="@+id/TextOutput"


>

</TextView>

</LinearLayout>

Run the application

To check out what your UI looks like, run the application; right click the project header and select‐Run As…/Android Application. The UI should look like below.

At runtime, the user interface components are created from the information in the XML file.‐The line

setContentView(R.layout.main);

in the TemperatureActivity.java tells the application which layout file to use (the name of our layout

file is main.xml).

You can have multiple layout files in our application and thus define multiple layouts.

Accessing UI components in the source code

You can access the UI components, defined in the XML file, from your application code through their‐id’s (e.g. “@+id/TextInput” for the EditText component) and the findViewById method.‐Open TemperatureActivity.java and add a member representing the ExitText and then call

findViewById to get a reference to the component.

public class TemperatureActivity extends Activity {

private EditText textInput;

public void onCreate(Bundle savedInstanceState) {



textInput = (EditText) findViewById(R.id.TextInput);

}

Add code to reference the buttons as well.

We then have to define what should happen when the calculate button is pressed (get the input

from the EditText and convert the value to degrees Celsius or Fahrenheit). This is done in a class

implementing the call back interface View.OnClickListener. Below you find the complete code.

public class TemperatureActivity extends Activity {

private EditText textInput ;

private RadioButton celciusButton;

private RadioButton fahrenheitButton;

private Button calculateButton;

private TextView textOutput;

@Override

public void onCreate(Bundle savedInstanceState) {



textInput = (EditText) findViewById(R.id.TextInput);

celciusButton = (RadioButton) findViewById(R.id.CelciusButton);

fahrenheitButton = (RadioButton) findViewById(R.id.FahrenheitButton);

calculateButton = (Button) findViewById(R.id.CalculateButton);

textOutput = (TextView) findViewById(R.id.TextOutput);

// Create a listener instance and associate it with the button

OnClickListener listener = new ButtonListener();

calculateButton.setOnClickListener(listener);

}

/**

* This class defines the action to take when the calculate button

* is clicked, in this case by calling buttonClickHandler().

*/

private class ButtonListener implements OnClickListener {

@Override

public void onClick(View v) {

buttonClickHandler();

}

}

private void buttonClickHandler() {

ring text = St textInput.getText().toString();

if(text.length() == 0) {

showToast("Please enter a a valid number");

return;

}

float value = Float.parseFloat(text);

String result = "";

if(celciusButton.isChecked()) {

float c = convertFahrenheitToCelsius(value);

result = "" + c + " Celsius";

}

else if(fahrenheitButton.isChecked()) {

float f = convertCelsiusToFahrenheit(value);

result = "" + f + " Fahrenheit";

}

else {

showToast("Please select a radio button");

return;

}

textOutput.setText(result);

}

private float convertFahrenheitToCelsius(float fahrenheit) {

return ((fahrenheit - 32) * 5 / 9);

}

private float convertCelsiusToFahrenheit(float celsius) {

return ((celsius * 9) / 5) + 32;

}

private void showToast(String msg) {

Toast toast = Toast.makeText(this, msg, Toast.LENGTH_SHORT);

toast.show();

}

}

Where to go from here…

I recommend you to continue with a more elaborate tutorial, the Note Pad Tutorial (1 3) at‐http://developer.android.com/resources/tutorials/notepad/index.html .

There are a lot of good tutorials on user interfaces, and other topics, at

http://developer.android.com/resources/tutorials/ .

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