iphone - 如何编写一个下载器类来更新 iOs 中的下载进度

Question

这是我的实际问题，正如一些人建议的那样，我想编写一个类来处理 UITableView 中的多个下载进度。我不知道如何为此编写课程，有人可以提供一些提示或想法吗？

Answer 1

要查看的组是 NSURLRequest 和 NSURLConnection。前者让您指定请求（URL、http 方法、参数等），后者运行它。

由于您想随时更新状态（我认为我在您的另一个问题中回答了这个草图），因此您需要实现 NSURLConnectionDelegate 协议，该协议在数据块从连接到达时移交它。如果您知道需要多少数据，您可以使用收到的数据量来计算我之前建议的 downloadProgress 浮点数：

float downloadProgress = [responseData length] / bytesExpected;

这是 SO 中一些漂亮的示例代码。您可以像这样扩展多个连接...

MyLoader.m

@interface MyLoader ()
@property (strong, nonatomic) NSMutableDictionary *connections;
@end

@implementation MyLoader
@synthesize connections=_connections;  // add a lazy initializer for this, not shown

// make it a singleton
+ (MyLoader *)sharedInstance {

    @synchronized(self) {
        if (!_sharedInstance) {
            _sharedInstance = [[MyLoader alloc] init];
        }
    }
    return _sharedInstance;
}

// you can add a friendlier one that builds the request given a URL, etc.
- (void)startConnectionWithRequest:(NSURLRequest *)request {

    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    NSMutableData *responseData = [[NSMutableData alloc] init];
    [self.connections setObject:responseData forKey:connection];
}

// now all the delegate methods can be of this form.  just like the typical, except they begin with a lookup of the connection and it's associated state
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

    NSMutableData *responseData = [self.connections objectForKey:connection];
    [responseData appendData:data];

    // to help you with the UI question you asked earlier, this is where
    // you can announce that download progress is being made
    NSNumber *bytesSoFar = [NSNumber numberWithInt:[responseData length]];
    NSDictionary *userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
        [connection URL], @"url", bytesSoFar, @"bytesSoFar", nil];

    [[NSNotificationCenter defaultCenter] postNotificationName:@"MyDownloaderDidRecieveData"
        object:self userInfo:userInfo];

    // the url should let you match this connection to the database object in
    // your view controller.  if not, you could pass that db object in when you
    // start the connection, hang onto it (in the connections dictionary) and
    // provide it in userInfo when you post progress
}

Answer 2

我写这个库就是为了做到这一点。您可以在 github 存储库中签出实现。