URL 编码问题

一般来说,我们通过使用 NSString 的stringByAddingPercentEscapesUsingEncoding函数来将字符串转换成可用的 URL,如下面这个例子:

NSString *string = @"this is a string";NSURL *url = [NSURL URLWithString:[string stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];NSLog(@"%@",url);

输入结果为

this%20is%20a%20string

但,当我们传入一些URL 的保留字符(例如&=+$)时,结果变成这样  
输入

NSString *string = @"this is a &=+$ string";

输出

this%20is%20a%20&=+$%20string

保留字符并没有没编码,这会导致我们将这个 URL 进行传输使用时,产生一些未知错误, 那么如何解决这个问题呢,苹果文档也在这个函数的说明中提供了相关资料.

Adds all percent escapes necessary to convert the receiver into a legal URL string. Uses the given encoding to determine the correct percent escapes (returning nil if the given encoding cannot encode a particular character).See CFURLCreateStringByAddingPercentEscapes in CFURL.h for more complex transformations

下面提供CFURLCreateStringByAddingPercentEscapes的用法,

- (NSString *) encodeURLFromString:(NSString *) string {    NSString *result;    CFStringRef encoded = CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,                                                                  (CFStringRef)string,                                                                  NULL,                                                                  (CFStringRef)@";/?:@&=+$,",                                                                  kCFStringEncodingUTF8);    result = (NSString *)CFBridgingRelease(encoded);    return result;}- (NSString *) decodeURLToString:(NSString *) url {    NSString *result;    CFStringRef decoded = CFURLCreateStringByReplacingPercentEscapes(kCFAllocatorDefault,                                                                     (CFStringRef)url,                                                                     CFSTR(""));    result = (NSString *)CFBridgingRelease(decoded);    return result;}

这样,编码时,我们调用CFURLCreateStringByAddingPercentEscapes函数,进行解析时使用CFURLCreateStringByReplacingPercentEscapes还原即可,仍使用上面这个例子

NSString *string = @"this is a &=+$ string";NSURL *url = [NSURL URLWithString:[self encodeURLFromString:string]];NSLog(@"%@",url);

输出结果变为

this%20is%20a%20%26%3D%2B%24%20string

这样,我们就解决了 URL 编码过程中的问题.