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The Android Open Source Project
2008-10-21 07:00:00 -07:00
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samples/RSSReader/src/com/example/android/rssreader/RssReader.java Normal file
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/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.rssreader;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import android.app.ListActivity;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.view.LayoutInflater;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.TwoLineListItem;
import android.util.Xml;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;
/**
* The RssReader example demonstrates forking off a thread to download
* rss data in the background and post the results to a ListView in the UI.
* It also shows how to display custom data in a ListView
* with a ArrayAdapter subclass.
*
* <ul>
* <li>We own a ListView
* <li>The ListView uses our custom RSSListAdapter which
* <ul>
* <li>The adapter feeds data to the ListView
* <li>Override of getView() in the adapter provides the display view
* used for selected list items
* </ul>
* <li>Override of onListItemClick() creates an intent to open the url for that
* RssItem in the browser.
* <li>Download = fork off a worker thread
* <li>The worker thread opens a network connection for the rss data
* <li>Uses XmlPullParser to extract the rss item data
* <li>Uses mHandler.post() to send new RssItems to the UI
* <li>Supports onSaveInstanceState()/onRestoreInstanceState() to save list/selection state on app
* pause, so can resume seamlessly
* </ul>
*/
public class RssReader extends ListActivity {
/**
* Custom list adapter that fits our rss data into the list.
*/
private RSSListAdapter mAdapter;
/**
* Url edit text field.
*/
private EditText mUrlText;
/**
* Status text field.
*/
private TextView mStatusText;
/**
* Handler used to post runnables to the UI thread.
*/
private Handler mHandler;
/**
* Currently running background network thread.
*/
private RSSWorker mWorker;
// Take this many chars from the front of the description.
public static final int SNIPPET_LENGTH = 90;
// Keys used for data in the onSaveInstanceState() Map.
public static final String STRINGS_KEY = "strings";
public static final String SELECTION_KEY = "selection";
public static final String URL_KEY = "url";
public static final String STATUS_KEY = "status";
/**
* Called when the activity starts up. Do activity initialization
* here, not in a constructor.
*
* @see Activity#onCreate
*/
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.rss_layout);
// The above layout contains a list id "android:list"
// which ListActivity adopts as its list -- we can
// access it with getListView().
// Install our custom RSSListAdapter.
List<RssItem> items = new ArrayList<RssItem>();
mAdapter = new RSSListAdapter(this, items);
getListView().setAdapter(mAdapter);
// Get pointers to the UI elements in the rss_layout
mUrlText = (EditText)findViewById(R.id.urltext);
mStatusText = (TextView)findViewById(R.id.statustext);
Button download = (Button)findViewById(R.id.download);
download.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
doRSS(mUrlText.getText());
}
});
// Need one of these to post things back to the UI thread.
mHandler = new Handler();
// NOTE: this could use the icicle as done in
// onRestoreInstanceState().
}
/**
* ArrayAdapter encapsulates a java.util.List of T, for presentation in a
* ListView. This subclass specializes it to hold RssItems and display
* their title/description data in a TwoLineListItem.
*/
private class RSSListAdapter extends ArrayAdapter<RssItem> {
private LayoutInflater mInflater;
public RSSListAdapter(Context context, List<RssItem> objects) {
super(context, 0, objects);
mInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
/**
* This is called to render a particular item for the on screen list.
* Uses an off-the-shelf TwoLineListItem view, which contains text1 and
* text2 TextViews. We pull data from the RssItem and set it into the
* view. The convertView is the view from a previous getView(), so
* we can re-use it.
*
* @see ArrayAdapter#getView
*/
@Override
public View getView(int position, View convertView, ViewGroup parent) {
TwoLineListItem view;
// Here view may be passed in for re-use, or we make a new one.
if (convertView == null) {
view = (TwoLineListItem) mInflater.inflate(android.R.layout.simple_list_item_2,
null);
} else {
view = (TwoLineListItem) convertView;
}
RssItem item = this.getItem(position);
// Set the item title and description into the view.
// This example does not render real HTML, so as a hack to make
// the description look better, we strip out the
// tags and take just the first SNIPPET_LENGTH chars.
view.getText1().setText(item.getTitle());
String descr = item.getDescription().toString();
descr = removeTags(descr);
view.getText2().setText(descr.substring(0, Math.min(descr.length(), SNIPPET_LENGTH)));
return view;
}
}
/**
* Simple code to strip out <tag>s -- primitive way to sortof display HTML as
* plain text.
*/
public String removeTags(String str) {
str = str.replaceAll("<.*?>", " ");
str = str.replaceAll("\\s+", " ");
return str;
}
/**
* Called when user clicks an item in the list. Starts an activity to
* open the url for that item.
*/
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
RssItem item = mAdapter.getItem(position);
// Creates and starts an intent to open the item.link url.
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(item.getLink().toString()));
startActivity(intent);
}
/**
* Resets the output UI -- list and status text empty.
*/
public void resetUI() {
// Reset the list to be empty.
List<RssItem> items = new ArrayList<RssItem>();
mAdapter = new RSSListAdapter(this, items);
getListView().setAdapter(mAdapter);
mStatusText.setText("");
mUrlText.requestFocus();
}
/**
* Sets the currently active running worker. Interrupts any earlier worker,
* so we only have one at a time.
*
* @param worker the new worker
*/
public synchronized void setCurrentWorker(RSSWorker worker) {
if (mWorker != null) mWorker.interrupt();
mWorker = worker;
}
/**
* Is the given worker the currently active one.
*
* @param worker
* @return
*/
public synchronized boolean isCurrentWorker(RSSWorker worker) {
return (mWorker == worker);
}
/**
* Given an rss url string, starts the rss-download-thread going.
*
* @param rssUrl
*/
private void doRSS(CharSequence rssUrl) {
RSSWorker worker = new RSSWorker(rssUrl);
setCurrentWorker(worker);
resetUI();
mStatusText.setText("Downloading\u2026");
worker.start();
}
/**
* Runnable that the worker thread uses to post RssItems to the
* UI via mHandler.post
*/
private class ItemAdder implements Runnable {
RssItem mItem;
ItemAdder(RssItem item) {
mItem = item;
}
public void run() {
mAdapter.add(mItem);
}
// NOTE: Performance idea -- would be more efficient to have he option
// to add multiple items at once, so you get less "update storm" in the UI
// compared to adding things one at a time.
}
/**
* Worker thread takes in an rss url string, downloads its data, parses
* out the rss items, and communicates them back to the UI as they are read.
*/
private class RSSWorker extends Thread {
private CharSequence mUrl;
public RSSWorker(CharSequence url) {
mUrl = url;
}
@Override
public void run() {
String status = "";
try {
// Standard code to make an HTTP connection.
URL url = new URL(mUrl.toString());
URLConnection connection = url.openConnection();
connection.setConnectTimeout(10000);
connection.connect();
InputStream in = connection.getInputStream();
parseRSS(in, mAdapter);
status = "done";
} catch (Exception e) {
status = "failed:" + e.getMessage();
}
// Send status to UI (unless a newer worker has started)
// To communicate back to the UI from a worker thread,
// pass a Runnable to handler.post().
final String temp = status;
if (isCurrentWorker(this)) {
mHandler.post(new Runnable() {
public void run() {
mStatusText.setText(temp);
}
});
}
}
}
/**
* Populates the menu.
*/
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
menu.add(0, 0, 0, "Slashdot")
.setOnMenuItemClickListener(new RSSMenu("http://rss.slashdot.org/Slashdot/slashdot"));
menu.add(0, 0, 0, "Google News")
.setOnMenuItemClickListener(new RSSMenu("http://news.google.com/?output=rss"));
menu.add(0, 0, 0, "News.com")
.setOnMenuItemClickListener(new RSSMenu("http://news.com.com/2547-1_3-0-20.xml"));
menu.add(0, 0, 0, "Bad Url")
.setOnMenuItemClickListener(new RSSMenu("http://nifty.stanford.edu:8080"));
menu.add(0, 0, 0, "Reset")
.setOnMenuItemClickListener(new MenuItem.OnMenuItemClickListener() {
public boolean onMenuItemClick(MenuItem item) {
resetUI();
return true;
}
});
return true;
}
/**
* Puts text in the url text field and gives it focus. Used to make a Runnable
* for each menu item. This way, one inner class works for all items vs. an
* anonymous inner class for each menu item.
*/
private class RSSMenu implements MenuItem.OnMenuItemClickListener {
private CharSequence mUrl;
RSSMenu(CharSequence url) {
mUrl = url;
}
public boolean onMenuItemClick(MenuItem item) {
mUrlText.setText(mUrl);
mUrlText.requestFocus();
return true;
}
}
/**
* Called for us to save out our current state before we are paused,
* such a for example if the user switches to another app and memory
* gets scarce. The given outState is a Bundle to which we can save
* objects, such as Strings, Integers or lists of Strings. In this case, we
* save out the list of currently downloaded rss data, (so we don't have to
* re-do all the networking just because the user goes back and forth
* between aps) which item is currently selected, and the data for the text views.
* In onRestoreInstanceState() we look at the map to reconstruct the run-state of the
* application, so returning to the activity looks seamlessly correct.
* TODO: the Activity javadoc should give more detail about what sort of
* data can go in the outState map.
*
* @see android.app.Activity#onSaveInstanceState
*/
@SuppressWarnings("unchecked")
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// Make a List of all the RssItem data for saving
// NOTE: there may be a way to save the RSSItems directly,
// rather than their string data.
int count = mAdapter.getCount();
// Save out the items as a flat list of CharSequence objects --
// title0, link0, descr0, title1, link1, ...
ArrayList<CharSequence> strings = new ArrayList<CharSequence>();
for (int i = 0; i < count; i++) {
RssItem item = mAdapter.getItem(i);
strings.add(item.getTitle());
strings.add(item.getLink());
strings.add(item.getDescription());
}
outState.putSerializable(STRINGS_KEY, strings);
// Save current selection index (if focussed)
if (getListView().hasFocus()) {
outState.putInt(SELECTION_KEY, Integer.valueOf(getListView().getSelectedItemPosition()));
}
// Save url
outState.putString(URL_KEY, mUrlText.getText().toString());
// Save status
outState.putCharSequence(STATUS_KEY, mStatusText.getText());
}
/**
* Called to "thaw" re-animate the app from a previous onSaveInstanceState().
*
* @see android.app.Activity#onRestoreInstanceState
*/
@SuppressWarnings("unchecked")
@Override
protected void onRestoreInstanceState(Bundle state) {
super.onRestoreInstanceState(state);
// Note: null is a legal value for onRestoreInstanceState.
if (state == null) return;
// Restore items from the big list of CharSequence objects
List<CharSequence> strings = (ArrayList<CharSequence>)state.getSerializable(STRINGS_KEY);
List<RssItem> items = new ArrayList<RssItem>();
for (int i = 0; i < strings.size(); i += 3) {
items.add(new RssItem(strings.get(i), strings.get(i + 1), strings.get(i + 2)));
}
// Reset the list view to show this data.
mAdapter = new RSSListAdapter(this, items);
getListView().setAdapter(mAdapter);
// Restore selection
if (state.containsKey(SELECTION_KEY)) {
getListView().requestFocus(View.FOCUS_FORWARD);
// todo: is above right? needed it to work
getListView().setSelection(state.getInt(SELECTION_KEY));
}
// Restore url
mUrlText.setText(state.getCharSequence(URL_KEY));
// Restore status
mStatusText.setText(state.getCharSequence(STATUS_KEY));
}
/**
* Does rudimentary RSS parsing on the given stream and posts rss items to
* the UI as they are found. Uses Android's XmlPullParser facility. This is
* not a production quality RSS parser -- it just does a basic job of it.
*
* @param in stream to read
* @param adapter adapter for ui events
*/
void parseRSS(InputStream in, RSSListAdapter adapter) throws IOException,
XmlPullParserException {
// TODO: switch to sax
XmlPullParser xpp = Xml.newPullParser();
xpp.setInput(in, null); // null = parser figures out encoding
int eventType;
String title = "";
String link = "";
String description = "";
eventType = xpp.getEventType();
while (eventType != XmlPullParser.END_DOCUMENT) {
if (eventType == XmlPullParser.START_TAG) {
String tag = xpp.getName();
if (tag.equals("item")) {
title = link = description = "";
} else if (tag.equals("title")) {
xpp.next(); // Skip to next element -- assume text is directly inside the tag
title = xpp.getText();
} else if (tag.equals("link")) {
xpp.next();
link = xpp.getText();
} else if (tag.equals("description")) {
xpp.next();
description = xpp.getText();
}
} else if (eventType == XmlPullParser.END_TAG) {
// We have a comlete item -- post it back to the UI
// using the mHandler (necessary because we are not
// running on the UI thread).
String tag = xpp.getName();
if (tag.equals("item")) {
RssItem item = new RssItem(title, link, description);
mHandler.post(new ItemAdder(item));
}
}
eventType = xpp.next();
}
}
// SAX version of the code to do the parsing.
/*
private class RSSHandler extends DefaultHandler {
RSSListAdapter mAdapter;
String mTitle;
String mLink;
String mDescription;
StringBuilder mBuff;
boolean mInItem;
public RSSHandler(RSSListAdapter adapter) {
mAdapter = adapter;
mInItem = false;
mBuff = new StringBuilder();
}
public void startElement(String uri,
String localName,
String qName,
Attributes atts)
throws SAXException {
String tag = localName;
if (tag.equals("")) tag = qName;
// If inside <item>, clear out buff on each tag start
if (mInItem) {
mBuff.delete(0, mBuff.length());
}
if (tag.equals("item")) {
mTitle = mLink = mDescription = "";
mInItem = true;
}
}
public void characters(char[] ch,
int start,
int length)
throws SAXException {
// Buffer up all the chars when inside <item>
if (mInItem) mBuff.append(ch, start, length);
}
public void endElement(String uri,
String localName,
String qName)
throws SAXException {
String tag = localName;
if (tag.equals("")) tag = qName;
// For each tag, copy buff chars to right variable
if (tag.equals("title")) mTitle = mBuff.toString();
else if (tag.equals("link")) mLink = mBuff.toString();
if (tag.equals("description")) mDescription = mBuff.toString();
// Have all the data at this point .... post it to the UI.
if (tag.equals("item")) {
RssItem item = new RssItem(mTitle, mLink, mDescription);
mHandler.post(new ItemAdder(item));
mInItem = false;
}
}
}
*/
/*
public void parseRSS2(InputStream in, RSSListAdapter adapter) throws IOException {
SAXParser parser = SAXParserFactory.newInstance().newSAXParser();
DefaultHandler handler = new RSSHandler(adapter);
parser.parse(in, handler);
// TODO: does the parser figure out the encoding right on its own?
}
*/
}