OC下载网络数据简介

同步下载

从网络上获取数据，有如下几种方式:

//百度首页#define BAIDU_URL @"http://www.baidu.com"//图片地址#define IMAGE_URL @"http://h.hiphotos.baidu.com/image/pic/item/5243fbf2b211931327b006b267380cd790238dc5.jpg"    // 请求字符串内容    NSURL * url = [NSURL URLWithString:BAIDU_URL];    NSString * strHtml = [[NSString alloc] initWithContentsOfURL:url encoding:NSUTF8StringEncoding error:nil];    // 从网络上请求图片数据    NSURL * imgUrl = [NSURL URLWithString:IMAGE_URL];    NSData * data = [NSData dataWithContentsOfURL:imgUrl];

异步下载

代理方式

    NSURLRequest * req = [NSURLRequest requestWithURL:[NSURL URLWithString:IMAGE_URL]];    // 通过设置代理回调方法，实现获取下载数据状态的值    [NSURLConnection connectionWithRequest:req delegate:self];#pragma mark- NSURLConnectionDelegate 代理的相关方法// 下载数据前- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {    NSLog(@"文件大小%lld byte, 文件名字: %@", response.expectedContentLength, response.suggestedFilename);    NSHTTPURLResponse * httpResponse = (NSHTTPURLResponse *) response;    NSLog(@"状态码：%ld", httpResponse.statusCode);    // 清空收到的数据    self.revData.length = 0;    // 设置状态栏下的网络请求状态    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];}// 正在下载中- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {    NSLog(@"追加字节数目：%ld", data.length);    [self.revData appendData:data];}// 下载完成后- (void)connectionDidFinishLoading:(NSURLConnection *)connection {    NSLog(@"下载完成，收到的字节总数: %ld", self.revData.length);    NSString * savePath = @"/Users/qf/Desktop/1.jpg";    [self.revData writeToFile:savePath atomically:YES];    // 设置状态栏下的网络请求状态    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];}

block回调

    NSURLRequest * req = [NSURLRequest requestWithURL:[NSURL URLWithString:IMAGE_URL]];    // 通过线程中主队列来辅助发送请求，下载完成之后即可获取整个数据的内容    [NSURLConnection sendAsynchronousRequest:req queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {        if (connectionError) {            NSLog(@"%@", connectionError);            return ;        }        NSString * savePath = [NSHomeDirectory() stringByAppendingString:@"/Documents/1.jpg"];        NSLog(@"savePath: %@", savePath);        [data writeToFile:savePath atomically:YES];        NSLog(@"下载完成!");    }];

SDWebImage 图像缓存库

简要使用方法如下。详细文档请参考 资源文件夹中 SDWebImage/README.md

    #import "UIImageView+WebCache.h"    [cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]

遇到问题

工程配置


App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app's Info.plist file.


【解决办法】

在工程文件 Info.plist中

添加 NSAppTransportSecurity 类型 Dictionary ;

在 NSAppTransportSecurity 下，
添加 NSAllowsArbitraryLoads 类型Boolean ,值设为 YES;