网络编程(GET, POST)

网络编程(GET, POST)

    客户端展示网络数据的过程:

    1.客户端发送请求给服务器端

    2.服务器端收到请求,把数据(XML, JSON)传给客户端

    3.客户端要对数据进行解析, 提取有用数据

    4.然后在控件(label, tableView, imageView等等)上进行展示

    客户端与服务器端进行沟通, 需要一定的规则(所谓的协议), 常用的协议:HTTP, 超文本传输协议

    HTTP请求的方式

    1.GET

    2.POST

    区别: 数据存放的位置不一样

    GET请求数据存放在网址(URL)的后面, ?前是URL, ?后是参数, 参数以key=value的形式出现, 多个键值对用&连接

    POST请求数据存放在请求体(HTTPBody)中

    注:请求的格式可以看接口文档(API文档)

    发出请求的方式:

    1.同步请求, 发出请求后,必须等待服务器的回应, 才能继续执行

    2.异步请求, 发出请求后, 无需等待服务器回应, 可以继续执行

同步GET请求

- (IBAction)get1:(id)sender {
   NSURL, 网址类
    NSURL *url = [NSURL URLWithString:@"http://api.hudong.com/iphonexml.do?type=focus-c"];
   NSURLRequest, 请求类, 继承于NSObject
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
   NSURLConnection, 网络连接类, 继承于NSObject, 用于发出请求
    //发出同步请求
    NSURLResponse *response = nil;
    NSError *error = nil;
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
    NSLog(@"response: %@ error: %@", response, error);
    NSLog(@"%@", data);
    将data转成NSString
    NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@", string);
    XML解析
//    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
}

同步POST请求

- (IBAction)post1:(id)sender {
    post请求的url后面没有参数
    NSURL *url = [NSURL URLWithString:@"http://api.hudong.com/iphonexml.do"];
    post请求的参数需要放在HTTPBody中, NSURLRequest不允许修改HTTPBody, 需要使用NSMutableURLRequest, 才能修改HTTPBody
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    请求体
    NSString *value = @"type=focus-c";
    request.HTTPBody = [value dataUsingEncoding:NSUTF8StringEncoding];
    请求方式, 默认为@"GET"
    request.HTTPMethod = @"POST";
    NSURLResponse *response = nil;
    NSError *error = nil;
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
    NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@", string);
    [string release];
}

异步GET请求

- (IBAction)get2:(id)sender {
    //1
    NSString *string = @"http://image.zcool.com.cn/56/13/1308200901454.jpg";
    URL中不能出现中文, 如果出现, 需要对字符串中的中文进行转码
    NSString *rightString = [string stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSLog(@"%@", rightString);
    NSURL *url = [NSURL URLWithString: rightString];
    //2
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    //3
    异步请求需要创建connection, 并指定delegate, 当数据返回时, 会调用代理方法
    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    //开始连接
    [connection start];
    //释放
    [connection release];
}

delegate方法

#pragma mark - NSURLConnectionDelegate
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"出现错误:%@", error);
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    NSLog(@"收到服务器的回应: %@", response);
    self.mData = [NSMutableData dataWithCapacity:0];
}

服务器传数据给客户端, 会把数据拆分成多个数据包, 这个方法会执行多次, 每次收到一个数据包就执行一次, 并且应该把数据包都拼接在一起, 形成完整的数据
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    NSLog(@"已经收到数据: %@", data);
    [self.mData appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"网络请求已经结束");
    self.imageView.image = [UIImage imageWithData:self.mData];
}

异步POST请求

- (IBAction)post2:(id)sender {
    //1
    NSURL *url = [NSURL URLWithString:@"http://api.tudou.com/v3/gw"];
    //2
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    NSString *valule = @"method=album.channel.get&appKey=myKey&format=json&channel=t&pageNo=1&pageSize=10";
    request.HTTPBody = [valule dataUsingEncoding:NSUTF8StringEncoding];
    request.HTTPMethod = @"POST";
    //3 发出异步请求
    //3.1
    //    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    //    [connection start];
    //    [connection release];
    //3.2
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        当请求结束才会执行block, 此时的data是一个完整的数据
        NSLog(@"%@", response);
        NSLog(@"%@", connectionError);
        NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"%@", string);
    }];
}

点击imageView出现图片

- (IBAction)tap:(id)sender {
    //1
    NSURL *url = [NSURL URLWithString:@"http://image.zcool.com.cn/56/13/1308200901454.jpg"];
    //2
    NSURLRequest *requst = [NSURLRequest requestWithURL:url];
    //3
    NSData *data = [NSURLConnection sendSynchronousRequest:requst returningResponse:nil error:nil];
    NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@", string);
    //4. NSData转UIImage
    UIImage *image = [UIImage imageWithData:data];
    //5,在UIImageView上展示图片
    self.imageView.image = image;
}

同步请求的缺点: 当数据比较大时, 由于需要等待服务器端把所有数据传过来, 如果网速比较慢, 就会造成应用程序"假死"状态(不能做其他操作, 必须等待数据全部传过来)实现代码:

#import "NewsTableViewController.h"
#import "XHNews.h"

@interface NewsTableViewController ()
- (IBAction)refresh:(id)sender;
@property (nonatomic, retain) NSMutableArray *dataArray;

@end

@implementation NewsTableViewController

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

- (void)viewDidLoad {
    [super viewDidLoad];

    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {

    // Return the number of rows in the section.
    return self.dataArray.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *identifier = @"identifier1";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:(UITableViewCellStyleSubtitle) reuseIdentifier:identifier] autorelease];
    }

    XHNews *news = [[XHNews alloc] init];
    news = self.dataArray[indexPath.row];
    cell.textLabel.text = news.title;
    cell.detailTextLabel.text = news.desc;
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:news.hot_pic]];
    cell.imageView.image = [UIImage imageWithData:data];
    return cell;
}

- (IBAction)refresh:(id)sender {
    //异步GET请求
    NSURL *url = [NSURL URLWithString:@"http://www.bjnews.com.cn/api/get_hotlist.php?page=1"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        NSLog(@"%@", response);
        NSLog(@"%@", connectionError);
        //JSON解析
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];
        NSLog(@"%@", dic);
        //数据封装
        self.dataArray = [NSMutableArray arrayWithCapacity:20];
        for (NSDictionary *dictionary in dic[@"list"]) {
            XHNews *news = [[XHNews alloc] init];
            [news setValuesForKeysWithDictionary:dictionary];
            [self.dataArray addObject:news];
            [news release];
        }
        NSLog(@"%@", self.dataArray);
        //展示数据(刷新tableView)
        [self.tableView reloadData];
    }];
}
@end