1 BOOL dataWillBeHandledExternally = NO;
 2 
 3 if ([[self delegate] respondsToSelector:[self didReceiveDataSelector]]) {
 4 
 5              //= YES会导致未下载完后离开下载页面后，程序会崩掉
 6 
 7 dataWillBeHandledExternally = NO;
 8 
 9 }
10 
11 #if NS_BLOCKS_AVAILABLE
12 
13 if (dataReceivedBlock) {
14 
15             //= YES会导致未下载完后离开下载页面后，程序会崩掉
16 
17 dataWillBeHandledExternally = NO;