说到http异步下载，首先要知道其中的关键类。
关键类是NSURLConnection NSURLRequest NSMutableURLRequest
委托是 NSURLConnectionDownloadDelegate NSURLConnectionDataDelegate NSURLConnectionDelegate
首先，我们要实现最基本的下载功能。
LQAsynDownload.h
//
// LQAsynDownload.h
// lgTest
//
// Created by yons on 14-2-14.
// Copyright (c) 2014年 GQ. All rights reserved.
// #import <Foundation/Foundation.h> @interface LQAsynDownload : NSObject<NSURLConnectionDataDelegate> @property (strong) NSURL *httpURL; + (LQAsynDownload *) initWithURL:(NSURL *) url; - (void) startAsyn; @end
LQAsynDownload.m
//
// LQAsynDownload.m
// lgTest
//
// Created by yons on 14-2-14.
// Copyright (c) 2014年 GQ. All rights reserved.
// #import "LQAsynDownload.h" @interface LQAsynDownload() @property (assign) long long contentLength; @property (assign) long long receiveLength; @property (strong) NSMutableData *receiveData; @property (strong) NSString *fileName; @property (strong) NSURLConnection *theConnection; @property (strong) NSURLRequest *theRequest; @end @implementation LQAsynDownload @synthesize receiveData = _receiveData, fileName = _fileName,
theConnection=_theConnection, theRequest=_theRequest; + (LQAsynDownload *) initWithURL:(NSURL *) url{
LQAsynDownload *asynDownload = [[LQAsynDownload alloc] init];
asynDownload.theRequest=[NSURLRequest requestWithURL:url
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
// create the connection with the request
// and start loading the data
return asynDownload;
} - (void) startAsyn{
_contentLength=0;
_receiveLength=0;
self.receiveData = [[NSMutableData alloc] init];
self.theConnection = [[NSURLConnection alloc] initWithRequest:self.theRequest delegate:self];
} //接收到http响应
- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
_contentLength = [response expectedContentLength];
_fileName = [response suggestedFilename];
NSLog(@"data length is %lli", _contentLength);
} //传输数据
-(void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
_receiveLength += data.length;
[_receiveData appendData:data];
NSLog(@"data recvive is %lli", _receiveLength);
} //错误
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
[self releaseObjs];
NSLog(@"%@",error.description);
} - (void) releaseObjs{
self.receiveData = nil;
self.fileName = nil;
self.theRequest = nil;
self.theConnection = nil;
} //成功下载完毕
- (void) connectionDidFinishLoading:(NSURLConnection *)connection{
//数据写入doument
//获取完整目录名字
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *savePath = [NSString stringWithFormat:@"%@/%@",documentsDirectory, _fileName];
//创建文件
[_receiveData writeToFile:savePath atomically:YES];
[self releaseObjs];
} @end
最简单的功能调用代码：
LQAsynDownload *dwn = [LQAsynDownload initWithURL:[[NSURL alloc] initWithString:@"http://t2.baidu.com/it/u=0,3067863433&fm=19&gp=0.jpg"]];
[dwn startAsyn];
查查模拟器，神啊，MM靓图出现了
情人节努力的补充礼物，哈哈。
关键点分析：
其实就是实现NSURLConnectionData委托的几个方法：
这个方法是客户端接收到回应后的调用方法，算是下载的开始。
- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
跟着就是接收数据的方法
-(void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
还有一个遇到错误时的处理方法
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
最后是下载成功调用的方法
- (void) connectionDidFinishLoading:(NSURLConnection *)connection
接着实现，下载进度查看。
在原代码基础上增加2个block 属性。
LQAsynDownload.h
1 //
2 // LQAsynDownload.h
3 // lgTest
4 //
5 // Created by yons on 14-2-14.
6 // Copyright (c) 2014年 GQ. All rights reserved.
7 //
8
9 #import <Foundation/Foundation.h>
10
11 typedef void (^initProgress)(long long initValue);
12
13 typedef void (^loadedData)(long long loadedLength);
14
15 @interface LQAsynDownload : NSObject<NSURLConnectionDataDelegate>
16
17 @property (strong) NSURL *httpURL;
18
19 @property (copy) void (^initProgress)(long long initValue);
20
21 @property (copy) void (^loadedData)(long long loadedLength);
22
23 + (LQAsynDownload *) initWithURL:(NSURL *) url;
24
25 - (void) startAsyn;
26
27 @end
LQAsynDownload.m
1 //
2 // LQAsynDownload.m
3 // lgTest
4 //
5 // Created by yons on 14-2-14.
6 // Copyright (c) 2014年 GQ. All rights reserved.
7 //
8
9 #import "LQAsynDownload.h"
10
11 @interface LQAsynDownload()
12
13 @property (assign) long long contentLength;
14
15 @property (assign) long long receiveLength;
16
17 @property (strong) NSMutableData *receiveData;
18
19 @property (strong) NSString *fileName;
20
21 @property (strong) NSURLConnection *theConnection;
22
23 @property (strong) NSURLRequest *theRequest;
24
25 @end
26
27 @implementation LQAsynDownload
28
29 @synthesize receiveData = _receiveData, fileName = _fileName,
30 theConnection=_theConnection, theRequest=_theRequest;
31
32 + (LQAsynDownload *) initWithURL:(NSURL *) url{
33 LQAsynDownload *asynDownload = [[LQAsynDownload alloc] init];
34 asynDownload.theRequest=[NSURLRequest requestWithURL:url
35 cachePolicy:NSURLRequestUseProtocolCachePolicy
36 timeoutInterval:60.0];
37 // create the connection with the request
38 // and start loading the data
39 return asynDownload;
40 }
41
42 - (void) startAsyn{
43 _contentLength=0;
44 _receiveLength=0;
45 self.receiveData = [[NSMutableData alloc] init];
46 self.theConnection = [[NSURLConnection alloc] initWithRequest:self.theRequest delegate:self];
47 }
48
49 //接收到http响应
50 - (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
51 _contentLength = [response expectedContentLength];
52 _fileName = [response suggestedFilename];
53 if (self.initProgress != nil) {
54 self.initProgress(_contentLength);
55 }
56 NSLog(@"data length is %lli", _contentLength);
57 }
58
59 //传输数据
60 -(void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
61 _receiveLength += data.length;
62 [_receiveData appendData:data];
63 if (self.loadedData != nil) {
64 self.loadedData(data.length);
65 }
66 NSLog(@"data recvive is %lli", _receiveLength);
67 }
68
69 //错误
70 - (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
71 [self releaseObjs];
72 NSLog(@"%@",error.description);
73 }
74
75 - (void) releaseObjs{
76 self.receiveData = nil;
77 self.fileName = nil;
78 self.theRequest = nil;
79 self.theConnection = nil;
80 }
81
82 //成功下载完毕
83 - (void) connectionDidFinishLoading:(NSURLConnection *)connection{
84 //数据写入doument
85 //获取完整目录名字
86 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
87 NSString *documentsDirectory = [paths objectAtIndex:0];
88 NSString *savePath = [NSString stringWithFormat:@"%@/%@",documentsDirectory, _fileName];
89 //创建文件
90 [_receiveData writeToFile:savePath atomically:YES];
91 [self releaseObjs];
92 }
93
94
95 @end
调用代码：
1 LQAsynDownload *dwn = [LQAsynDownload initWithURL:[[NSURL alloc] initWithString:@"http://a.hiphotos.baidu.com/image/w%3D2048/sign=fae75ab5d63f8794d3ff4f2ee6230ff4/faedab64034f78f09f9423fe7b310a55b3191c1b.jpg"]];
2
3 dwn.initProgress = ^(long long initValue){
4 _sum = initValue;
5 NSLog(@"%lli",initValue);
6 _rcv = 0;
7 dispatch_async(dispatch_get_main_queue(), ^{
8 self.pv.progress = 0.0;
9 self.pv.hidden = NO;
10 });
11 };
12
13 dwn.loadedData = ^(long long loadedLength){
14 dispatch_async(dispatch_get_main_queue(), ^{
15 if (_rcv == _sum) {
16 self.pv.hidden = YES;
17 } else {
18 _rcv += loadedLength;
19 self.pv.progress = _rcv/_sum;
20 }
21 });
22 };
23
24 [dwn startAsyn];
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