iOS中下载大型文件的原理解析二

最新推荐文章于 2019-07-23 15:01:41 发布

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最新推荐文章于 2019-07-23 15:01:41 发布

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分类专栏： IOS开发文章标签： ios

本文链接：https://blog.youkuaiyun.com/jiandanjinxin/article/details/50600301

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本文详细介绍了在iOS环境中使用NSURLConnection进行大型文件下载的方法，并提供了具体的代码实现。通过创建空文件、获取文件句柄、接收并写入数据以及处理下载完成后的关闭操作，实现了高效稳定的文件下载流程。

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在iOS中下载大型文件，需要使用NSURLConnection 的代理方法：

(void)touchesBegan:(NSSet)touches withEvent:(UIEvent *)event {
NSURL *url = [NSURL URLWithString:@”http://d.3987.com/fengj_141112/007.jpg“];
NSURLRequest *request = [NSURLRequest requestWithURL:url];

[NSURLConnection connectionWithRequest:request delegate:self];
}
(void)connection:(NSURLConnection )connection didFailWithError:(NSError )error {
NSLog(@”didFailWithError:%@”, [NSThread currentThread]);

}

(void)connection:(NSURLConnection )connection didReceiveResponse:(NSURLResponse )response {
NSLog(@”didReceiveResponse:%@”, [NSThread currentThread]);

NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
NSString *filePath = [caches stringByAppendingPathComponent:@”videos.zip”];
NSFileManager * fileManager = [NSFileManager defaultManager];
[fileManager createFileAtPath:filePath contents:nil attributes:nil];

self.writeHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];

self.fileLength = response.expectedContentLength;
}
(void)connection:(NSURLConnection )connection didReceiveData:(NSData )data {
NSLog(@”didReceiveData:%@”, [NSThread currentThread]);
[self.writeHandle seekToEndOfFile];
[self.writeHandle writeData:data];

self.currentLength += data.length;

NSLog(@”下载进度： %f”, (double)self.currentLength / self.fileLength);

}

(void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(@”connectionDidFinishLoading:%@”, [NSThread currentThread]);
self.currentLength = 0;
self.fileLength = 0;
[self.writeHandle closeFile];
self.writeHandle = nil;
}

总体思路：
（1）首先创建一个空的文件：
NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
NSString *filePath = [caches stringByAppendingPathComponent:@”videos.zip”];
NSFileManager * fileManager = [NSFileManager defaultManager];
[fileManager createFileAtPath:filePath contents:nil attributes:nil];
（2）其次获取操作这个文件的句柄
self.writeHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
（3）当数据到来后，需要将其写入到文件中去
[self.writeHandle seekToEndOfFile];
[self.writeHandle writeData:data];
（4）最后在文件下载完毕后，需要关闭文件

[self.writeHandle closeFile];