SeismicXML范例解析

 SeismicXML例子程序演示如何使用NSXMLParser分析XML数据，主要分析从USGS的RSS feed。USGS提供世界各地的最近地震。它显示每个地震的位置，日期，震级。同时用颜色图形显示地震的严重性。此XML在后台分析且用分析的对象更新地震table view。
此代码中包含了一些比较好的思想，如多线程分析xml数据，异步下载，NSNotificationCente(在两个类中传递数据)，UIActionSheet类实现，和其它一些技术细节。

官方例子相关：
SeismicXML地址：http://developer.apple.com/iphone/library/samplecode/SeismicXML/SeismicXML.zip

 

一、程序的运行效果

二、程序的思路
多线程的好处即提高程序执行效率，防止界面阻塞。
1、进入程序后，建立给定网址(RSS feed)的连接，程序会自动下载对应的RSS feed数据，如果网络连接无误，数据自动全部下载，这是XCode提供的内部回调函数。
2、增加消息中心，以便地震RSS feed解析成功或失败时通知
3、建立一个线程，把下载好的数据传递给新建线程类，把此线程添加到线程队列，通过注册的消息中心来通知被处理的数据，这点与LazyTableImages有区别，LazyTableImage是利用XCode的delegate等待线程结束后返回被处理后的数据。
3、在创建的线程中用NSXMLParser根据程序要求分析下载的数据，并添加到数组中。全部解析之后，通知AppDelegate
4、从线程类接到解析成功通知后，根据通知参数NSNotification指针，调用table view视图rootViewController，插入解析好的数组

下面记录一些具体的代码实现
1、网络连接并下载数据

声明
@interface SeismicXMLAppDelegate : NSObject  
{
    NSURLConnection *earthquakeFeedConnection; 
	NSMutableData *earthquakeData;	
}
实现
@interface SeismicXMLAppDelegate ()

@property (nonatomic, retain) NSURLConnection *earthquakeFeedConnection;
@property (nonatomic, retain) NSMutableData *earthquakeData;    
@end

#pragma mark -
#pragma mark SeismicXMLAppDelegate

@implementation SeismicXMLAppDelegate

@synthesize earthquakeFeedConnection;
@synthesize earthquakeData;

- (void)dealloc 
{
    [earthquakeFeedConnection cancel];
    [earthquakeFeedConnection release];
    
    [earthquakeData release];
    [super dealloc];
}
- (void)applicationDidFinishLaunching:(UIApplication *)application 
{
    static NSString *feedURLString = @"http://earthquake.usgs.gov/eqcenter/catalogs/7day-M2.5.xml";
    NSURLRequest *earthquakeURLRequest =
    [NSURLRequest requestWithURL:[NSURL URLWithString:feedURLString]];
    self.earthquakeFeedConnection =
    [[[NSURLConnection alloc] initWithRequest:earthquakeURLRequest delegate:self] autorelease];
    NSAssert(self.earthquakeFeedConnection != nil, @"Failure to create URL connection.");
}

#pragma mark -
#pragma mark NSURLConnection delegate methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response 
{
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    if ((([httpResponse statusCode]/100) == 2) && [[response MIMEType] isEqual:@"application/atom+xml"])
	{
        self.earthquakeData = [NSMutableData data];
    } 
	else 
	{
        NSDictionary *userInfo = [NSDictionary dictionaryWithObject:
                                  NSLocalizedString(@"HTTP Error",
                                                    @"Error message displayed when receving a connection error.")
                                                             forKey:NSLocalizedDescriptionKey];
        NSError *error = [NSError errorWithDomain:@"HTTP" code:[httpResponse statusCode] userInfo:userInfo];
        [self handleError:error];
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data 
{
    [earthquakeData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error 
{
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;   
    if ([error code] == kCFURLErrorNotConnectedToInternet)
	{
        NSDictionary *userInfo =
        [NSDictionary dictionaryWithObject:
         NSLocalizedString(@"No Connection Error",
                           @"Error message displayed when not connected to the Internet.")
                                    forKey:NSLocalizedDescriptionKey];
        NSError *noConnectionError = [NSError errorWithDomain:NSCocoaErrorDomain
                                                         code:kCFURLErrorNotConnectedToInternet
                                                     userInfo:userInfo];
        [self handleError:noConnectionError];
    }
	else
	{
        // otherwise handle the error generically
        [self handleError:error];
    }
    self.earthquakeFeedConnection = nil;
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{
    self.earthquakeFeedConnection = nil;
    ParseOperation *parseOperation = [[ParseOperation alloc] initWithData:self.earthquakeData];
    [self.parseQueue addOperation:parseOperation];
    [parseOperation release];   // once added to the NSOperationQueue it's retained, we don't need it anymore
    
    self.earthquakeData = nil;
}

2、创建线程队列并把新建线程增加到队列中 

头文件
@interface SeismicXMLAppDelegate : NSObject 
{  
@private
    NSOperationQueue *parseQueue; 
}
实现
#import "ParseOperation.h"

#pragma mark SeismicXMLAppDelegate () 
@interface SeismicXMLAppDelegate ()
@property (nonatomic, retain) NSOperationQueue *parseQueue;  
@end

#pragma mark -
#pragma mark SeismicXMLAppDelegate
@implementation SeismicXMLAppDelegate
@synthesize parseQueue;

- (void)dealloc 
{
    [parseQueue release];
    [super dealloc];
}

- (void)applicationDidFinishLaunching:(UIApplication *)application 
{
    parseQueue = [NSOperationQueue new]; 
}

#pragma mark -
#pragma mark NSURLConnection delegate methods
- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{
    ParseOperation *parseOperation = [[ParseOperation alloc] initWithData:self.earthquakeData];
    [self.parseQueue addOperation:parseOperation];
    [parseOperation release];
}
@end

3、增加通知中心

AppDelegate中实现
- (void)dealloc 
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:kAddEarthquakesNotif object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:kEarthquakesErrorNotif object:nil];
        [super dealloc];
}
- (void)applicationDidFinishLaunching:(UIApplication *)application 
{
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(addEarthquakes:)
                                                 name:kAddEarthquakesNotif
                                               object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(earthquakesError:)
                                                 name:kEarthquakesErrorNotif
                                               object:nil];
}
- (void)addEarthquakes:(NSNotification *)notif
{
    assert([NSThread isMainThread]);
    
    [self addEarthquakesToList:[[notif userInfo] valueForKey:kEarthquakeResultsKey]];
}
- (void)earthquakesError:(NSNotification *)notif
{
    assert([NSThread isMainThread]);
    
    [self handleError:[[notif userInfo] valueForKey:kEarthquakesMsgErrorKey]];
}
- (void)addEarthquakesToList:(NSArray *)earthquakes
{
    [self.rootViewController insertEarthquakes:earthquakes];
}
线程头文件ParseOperation.h
extern NSString *kAddEarthquakesNotif;
extern NSString *kEarthquakeResultsKey;

extern NSString *kEarthquakesErrorNotif;
extern NSString *kEarthquakesMsgErrorKey;
线程实现文件ParseOperation.m
NSString *kAddEarthquakesNotif = @"AddEarthquakesNotif";
NSString *kEarthquakeResultsKey = @"EarthquakeResultsKey";
NSString *kEarthquakesErrorNotif = @"EarthquakeErrorNotif";
NSString *kEarthquakesMsgErrorKey = @"EarthquakesMsgErrorKey";
- (void)addEarthquakesToList:(NSArray *)earthquakes 
{
    assert([NSThread isMainThread]);
    
    [[NSNotificationCenter defaultCenter] postNotificationName:kAddEarthquakesNotif
                                                        object:self
                                                      userInfo:[NSDictionary dictionaryWithObject:earthquakes
                                                                                           forKey:kEarthquakeResultsKey]]; 
}
- (void)handleEarthquakesError:(NSError *)parseError {
    [[NSNotificationCenter defaultCenter] postNotificationName:kEarthquakesErrorNotif
                                                    object:self
                                                  userInfo:[NSDictionary dictionaryWithObject:parseError
                                                                                       forKey:kEarthquakesMsgErrorKey]];
}

4、格式化日期

头文件：ParseOperation.h
@private
NSDateFormatter *dateFormatter;
实现文件ParseOperation.m
- (id)initWithData:(NSData *)parseData
{
    if (self = [super init]) 
	{    
        dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
        [dateFormatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease]];
		//Aug 5,2011 11:39:30 PM
        [dateFormatter setDateFormat:@"yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"];
}
｝
- (void)dealloc 
{
    [dateFormatter release];
}
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
                                      namespaceURI:(NSString *)namespaceURI
                                     qualifiedName:(NSString *)qName
{   
  self.currentEarthquakeObject.date =
            [dateFormatter dateFromString:self.currentParsedCharacterData];
}
头文件：RootViewController.h
@interface RootViewController : UITableViewController  {
    NSDateFormatter *dateFormatter;
}
@property (nonatomic, retain, readonly) NSDateFormatter *dateFormatter;
实现文件RootViewController.m
- (void)dealloc {
     [dateFormatter release];
    [super dealloc];
}
- (NSDateFormatter *)dateFormatter {
    if (dateFormatter == nil) {
        dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
        [dateFormatter setDateStyle:NSDateFormatterMediumStyle];
        [dateFormatter setTimeStyle:NSDateFormatterMediumStyle];
    }
    return dateFormatter;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
     dateLabel.text = [NSString stringWithFormat:@"%@", [self.dateFormatter stringFromDate:earthquake.date]];
 	return cell;
}

5、分解字符串

//