如何知道NSData的initWithContentsOfURL何時完成加載。

Question

我正在從xml和圖像中加載一些文本，該圖像比xml加載時間要長，但我想同時顯示它們。

我加載使用

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

如何設置一個回調函數，讓我知道mydata有圖像的圖像，這樣我就可以同時添加圖像和文本的看法？

謝謝

Answer 1

您將不得不使用NSURLConnection。這相當簡單，但比NSData方法涉及更多。

首先，創建一個NSURLConnection的：

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 
} 

現在，添加<NSURLConnectionDelegate>到類的頭和實現以下方法：

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

第一個應該追加數據，如下所示，最後一個應該創建並顯示圖像。

- (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]; 
} 

查看this document瞭解更多詳情。