NSURLConnection 中的恢复下载功能

NSURLConnection 中的恢复下载功能

objc
// 在 ViewController.m 文件中，添加以下代码
#import "ViewController.h"
@interface ViewController () 
@property (nonatomic, strong) NSURLConnection *connection;
@property (nonatomic, strong) NSMutableData *responseData;
@property (nonatomic, assign) long long totalLength;
@property (nonatomic, assign) long long currentLength;
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 创建 NSURLRequest 对象
    NSURL *url = [NSURL URLWithString:@"http://example.com/file.zip"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    
    // 设置请求头的 Range 字段，用于恢复下载
    NSString *range = [NSString stringWithFormat:@"bytes=%lld-", self.currentLength];
    [request setValue:range forHTTPHeaderField:@"Range"];
    
    // 发起网络请求
    self.connection = [NSURLConnection connectionWithRequest:request delegate:self];
}
#pragma mark - NSURLConnectionDelegate
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    // 获取文件总长度
    self.totalLength = response.expectedContentLength;
    
    // 创建 NSMutableData 对象，用于保存已下载的数据
    self.responseData = [NSMutableData data];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    // 将下载的数据追加到 responseData 中
    [self.responseData appendData:data];
    
    // 计算已下载的数据长度
    self.currentLength += data.length;
    
    // 更新下载进度
    float progress = (float)self.currentLength / self.totalLength;
    NSLog(@"下载进度：%.2f%", progress * 100);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // 下载完成后，保存文件到本地
    NSString *filePath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
    filePath = [filePath stringByAppendingPathComponent:@"file.zip"];
    [self.responseData writeToFile:filePath atomically:YES];
    
    NSLog(@"文件下载完成，保存路径：%@", filePath);
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"文件下载失败，错误信息：%@", error.localizedDescription);
}
@end