如何知道NSData的initWithContentsOfURL何时完成加载.

Question

我正在从xml和图像加载一些文本,该图像加载比xml需要更长的时间,但我想同时显示它们.

我正在使用加载图像

NSData *mydata = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:imgLink]];

如何设置一个让我知道mydata有图像的回调函数,这样我就可以将图像和文本添加到视图中？

谢谢

Answer 1

您将不得不使用NSURLConnection.这相当简单,但比NSData方法更复杂.

首先,创建一个NSURLConnection:

NSMutableData *receivedData;

NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:imgLink]
                                          cachePolicy:NSURLRequestUseProtocolCachePolicy
                                      timeoutInterval:60.0];

NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

 if (theConnection) {
    receivedData=[[NSMutableData data] retain];
} else {
    // inform the user that the download could not be made
}

现在,将<NSURLConnectionDelegate>添加到类的标头并实现以下方法:

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;

第一个应该附加数据,如下所示,最后一个应该创建并显示图像.

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
{
    // append the new data to the receivedData
    // receivedData is declared as a method instance elsewhere
    [receivedData appendData:data];
}

有关详细信息,请参阅此文档.