iOS网络编程

一、检测网络状态

添加源文件和framework

开发Web等网络应用程序的时候,需要确认网络环境,连接情况等信息。如果没有处理它们,是不会通过Apple的审(我们的)查的。
Apple 的例程 Reachability 中介绍了取得/检测网络状态的方法。要在应用程序程序中使用Reachability,首先要完成如下两部:

  1. 添加源文件:
    在你的程序中使用 Reachability 只须将该例程中的 Reachability.h 和 Reachability.m 拷贝到你的工程中。如下图:
  2. 添加framework:
    将SystemConfiguration.framework 添加进工程。如下图:

网络状态

Reachability.h中定义了三种网络状态:

typedef enum {
    NotReachable = 0,            //无连接
    ReachableViaWiFi,            //使用3G/GPRS网络
    ReachableViaWWAN            //使用WiFi网络
} NetworkStatus;

因此可以这样检查网络状态:

Reachability *r = [Reachability reachabilityWithHostName:@“www.apple.com”];
switch ([r currentReachabilityStatus]) {
        case NotReachable:
                // 没有网络连接
                break;
        case ReachableViaWWAN:
                // 使用3G网络
                break;
        case ReachableViaWiFi:
                // 使用WiFi网络
                break;
}

检查当前网络环境

程序启动时,如果想检测可用的网络环境,可以像这样

// 是否wifi
+ (BOOL) IsEnableWIFI {
    return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable);
}

// 是否3G
+ (BOOL) IsEnable3G {
    return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable);
}


- (void)viewWillAppear:(BOOL)animated {    
if (([Reachability reachabilityForInternetConnection].currentReachabilityStatus == NotReachable) && 
        ([Reachability reachabilityForLocalWiFi].currentReachabilityStatus == NotReachable)) {
        self.navigationItem.hidesBackButton = YES;
        [self.navigationItem setLeftBarButtonItem:nil animated:NO];
    }
}

链接状态的实时通知

网络连接状态的实时检查,通知在网络应用中也是十分必要的。接续状态发生变化时,需要及时地通知用户:

Reachability 1.5版本

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// MyAppDelegate.h
#import "Reachability.h"

@interface MyAppDelegate : NSObject <UIApplicationDelegate> {
NetworkStatus remoteHostStatus;
}

@property NetworkStatus remoteHostStatus;

@end

// My.AppDelegate.m
#import "MyAppDelegate.h"

@implementation MyAppDelegate
@synthesize remoteHostStatus;

// 更新网络状态
- (void)updateStatus {
self.remoteHostStatus = [[Reachability sharedReachability] remoteHostStatus];
}

// 通知网络状态
- (void)reachabilityChanged:(NSNotification *)note {
[self updateStatus];
if (self.remoteHostStatus == NotReachable) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:NSLocalizedString(@"AppName", nil)
message:NSLocalizedString (@"NotReachable", nil)
delegate:nil cancelButtonTitle:@"OK" otherButtonTitles: nil];
[alert show];
[alert release];
}
}

// 程序启动器,启动网络监视
- (void)applicationDidFinishLaunching:(UIApplication *)application {

// 设置网络检测的站点
[[Reachability sharedReachability] setHostName:@"www.apple.com"];
[[Reachability sharedReachability] setNetworkStatusNotificationsEnabled:YES];
// 设置网络状态变化时的通知函数
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:)
name:@"kNetworkReachabilityChangedNotification" object:nil];
[self updateStatus];
}

- (void)dealloc {
// 删除通知对象
[[NSNotificationCenter defaultCenter] removeObserver:self];
[window release];
[super dealloc];
}

Reachability 2.0版本

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// MyAppDelegate.h
#import "Reachability.h"
@class Reachability;
@interface MyAppDelegate : NSObject <UIApplicationDelegate> {
Reachability *hostReach;
}
@end

// MyAppDelegate.m
#import "MyAppDelegate.h"
@implementation MyAppDelegate
- (void)reachabilityChanged:(NSNotification *)note {
Reachability* curReach = [note object];
NSParameterAssert([curReach isKindOfClass: [Reachability class]]);
NetworkStatus status = [curReach currentReachabilityStatus];

if (status == NotReachable) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"AppName""
message:@"NotReachable"
delegate:nil
cancelButtonTitle:@"YES" otherButtonTitles:nil];
[alert show];
[alert release];
}
}

- (void)applicationDidFinishLaunching:(UIApplication *)application {
// ...

// 监测网络情况
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(reachabilityChanged:)
name: kReachabilityChangedNotification
object: nil];
hostReach = [[Reachability reachabilityWithHostName:@"www.google.com"] retain];
hostReach startNotifer];
// ...
}
@end

二、使用NSConnection下载数据

1.创建NSConnection对象,设置委托对象

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NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self urlString]]];
[NSURLConnection connectionWithRequest:request delegate:self];

  1. NSURLConnection delegate委托方法
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- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;  
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;
  1. 实现委托方法
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    - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    // store data
    [self.receivedData setLength:0]; //通常在这里先清空接受数据的缓存
    }

    - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    /* appends the new data to the received data */
    [self.receivedData appendData:data]; //可能多次收到数据,把新的数据添加在现有数据最后
    }

    - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    // 错误处理
    }

    - (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // disconnect
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    NSString *returnString = [[NSString alloc] initWithData:self.receivedData encoding:NSUTF8StringEncoding];
    NSLog(returnString);
    [self urlLoaded:[self urlString] data:self.receivedData];
    firstTimeDownloaded = YES;
    }

三、使用NSXMLParser解析xml文件

  1. 设置委托对象,开始解析

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    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];   //或者也可以使用initWithContentsOfURL直接下载文件,但是有一个原因不这么做:
    // It's also possible to have NSXMLParser download the data, by passing it a URL, but this is not desirable
    // because it gives less control over the network, particularly in responding to connection errors.
    [parser setDelegate:self];
    [parser parse];
  2. 常用的委托方法

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    - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName 
    namespaceURI:(NSString *)namespaceURI
    qualifiedName:(NSString *)qName
    attributes:(NSDictionary *)attributeDict;
    - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
    namespaceURI:(NSString *)namespaceURI
    qualifiedName:(NSString *)qName;
    - (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string;
    - (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError;
    static NSString *feedURLString = @"http://www.yifeiyang.net/test/test.xml";
  3. 应用举例

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    - (void)parseXMLFileAtURL:(NSURL *)URL parseError:(NSError **)error
    {
    NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:URL];
    [parser setDelegate:self];
    [parser setShouldProcessNamespaces:NO];
    [parser setShouldReportNamespacePrefixes:NO];
    [parser setShouldResolveExternalEntities:NO];
    [parser parse];
    NSError *parseError = [parser parserError];
    if (parseError && error) {
    *error = parseError;
    }
    [parser release];
    }

    - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI
    qualifiedName:(NSString*)qName attributes:(NSDictionary *)attributeDict{
    // 元素开始句柄
    if (qName) {
    elementName = qName;
    }
    if ([elementName isEqualToString:@"user"]) {
    // 输出属性值
    NSLog(@"Name is %@ , Age is %@", [attributeDict objectForKey:@"name"], [attributeDict objectForKey:@"age"]);
    }
    }

    - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI
    qualifiedName:(NSString *)qName
    {
    // 元素终了句柄
    if (qName) {
    elementName = qName;
    }
    }

    - (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
    {
    // 取得元素的text
    }

    NSError *parseError = nil;
    [self parseXMLFileAtURL:[NSURL URLWithString:feedURLString] parseError:&parseError];

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