ios - IOS stringByReplacingOccurrencesOfString 返回 null

Question

我一直在用头撞墙，我一定错过了什么。在我对一些加密文本进行 base64 编码之后，就会调用此代码。在我调用 NSLog 签名的地方总是有效的。然而，有时其余的效果很好，而其他时候 removePlus 或 finalSig 则返回 null。此外，我使用的是 Xcode 4.5、ios6，并且我为该项目启用了 ARC。我觉得可能有些东西在我想要之前就自动发布了，或者类似的东西。如果有人有任何想法，我们将不胜感激。

// Get the data out of the context
char *outputBuffer;
long outputLength = BIO_get_mem_data(context, &outputBuffer);

NSMutableString *signature = [[NSMutableString alloc] init];
[signature appendString:[NSMutableString stringWithCString:outputBuffer encoding:NSASCIIStringEncoding]];

NSLog(@"Base64 Pre Encoded: %@", signature);

signature = [[signature stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding] mutableCopy];
NSMutableString *removePlus = [[signature stringByReplacingOccurrencesOfString:@"+" withString:@"%2B"] mutableCopy];
NSString *finalSig = [removePlus stringByReplacingOccurrencesOfString:@"=" withString:@"%3D"];

//now we create the url request portion
NSMutableString *variables = [[NSMutableString alloc] init];

//set the variables we're going
[variables appendString:finalSig];

Answer 1

尝试将您的代码换成以下代码，因为我想它会准确地告诉您问题出在哪里：

// Get the data out of the context
char *outputBuffer;
long outputLength = BIO_get_mem_data(context, &outputBuffer);

outputBuffer[outputLength] = '\0';
if(outputLength != strlen(outputBuffer)) NSLog(@"SOMETHING VERY WRONG");

NSString * signature = [NSString stringWithCString:outputBuffer encoding:NSASCIIStringEncoding]];
NSLog(@"Base64 Pre Encoded: %@", signature);

signature = [[signature stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding];
NSLog(@"Base64 Post Encoded: %@", signature);

signature = [signature stringByReplacingOccurrencesOfString:@"+" withString:@"%2B"];
NSLog(@"Base64 Remove '+': %@", signature);

signature = [removePlus stringByReplacingOccurrencesOfString:@"=" withString:@"%3D"];
NSLog(@"Base64 Remove '=': %@", signature);

//now we create the url request portion
NSMutableString *variables = [NSMutableString alloc] initWithString:signature];

…

//set the variables we're going
[variables appendString:finalSig];

Answer 2

原来 NSString * signature = [NSString stringWithCString:outputBuffer encoding:NSASCIIStringEncoding]]; 需要一个以空字符结尾的字符串，而我的字符串不是。无论如何，这是创建字符串的更有效方法：

NSData *myRequestData = [ NSData dataWithBytes: [ variables UTF8String ] length: [ variables length ] ];