Parameters
URLString
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The string with which to initialize the NSURL object. This string must conform to URL format as described in RFC 2396. This method parses URLString according to RFCs 1738 and 1808.
Discussion
This method expects URLString to contain any necessary percent escape codes, which are ‘:’, ‘/’, ‘%’, ‘#’, ‘;’, and ‘@’. Note that ‘%’ escapes are translated via UTF-8.
所以URLString中有空格的要变成：%20
[urlstring stringByReplacingOccurrencesOfString:@" "withString:@"%20"]]
然后还要进行编码转换
str=[str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];