如何在NSString中获取NSData值

Question

我尝试了以下

-(void)imagePickerController:(UIImagePickerController*)picker didFinishPickingMediaWithInfo:(NSDictionary*)info
{
  imagedata = UIImageJPEGRepresentation([info objectForKey:@"UIImagePickerControllerOriginalImage"],1); 

  NSString *s1 = [[[NSString alloc]initWithData:imagedata encoding:NSUTF8StringEncoding]autorelease];

  NSString *s2 = [[[NSString alloc]  initWithBytes:[imagedata bytes]
                                              length:[imagedata length] encoding: NSUTF8StringEncoding]autorelease];

  NSString *s3 = [NSString stringWithUTF8String:[imagedata bytes]];


  [picker dismissModalViewControllerAnimated:YES];

}

如果在调试器控制台中看到imagedata的打印说明：，我可以在其中看到blob值。 但是我无法在NSString中得到所有上述s1，s2，s3返回空值。 我想将图像的Blob值上传到远程服务器数据库。 解决方案是什么？

Answer 1

您正在尝试使用各种编码方法将图像转换为NSString，这将使您返回null，因为您无法将UIImage转换为NSString。

另一种方法是使用base64编码函数将其转换为NSString在您的类中添加以下代码：

static char base64EncodingTable[64] = 
{
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
};

@implementation NSString (NSStringAdditions)

+ (NSString *) base64StringFromData: (NSData *)data length: (int)length 
{
    unsigned long ixtext, lentext;
    long ctremaining;
    unsigned char input[3], output[4];
    short i, charsonline = 0, ctcopy;
    const unsigned char *raw;
    NSMutableString *result;

    lentext = [data length]; 
    if (lentext < 1)
        return @"";
    result = [NSMutableString stringWithCapacity: lentext];
    raw = [data bytes];
    ixtext = 0; 

    while (true) 
    {
        ctremaining = lentext - ixtext;
        if (ctremaining <= 0) 
            break;        
        for (i = 0; i < 3; i++) 
        { 
            unsigned long ix = ixtext + i;
            if (ix < lentext)
                input[i] = raw[ix];
            else
                input[i] = 0;
        }
        output[0] = (input[0] & 0xFC) >> 2;
        output[1] = ((input[0] & 0x03) << 4) | ((input[1] & 0xF0) >> 4);
        output[2] = ((input[1] & 0x0F) << 2) | ((input[2] & 0xC0) >> 6);
        output[3] = input[2] & 0x3F;
        ctcopy = 4;
        switch (ctremaining) 
        {
            case 1: 
                ctcopy = 2; 
                break;
            case 2: 
                ctcopy = 3; 
                break;
        }

        for (i = 0; i < ctcopy; i++)
            [result appendString: [NSString stringWithFormat: @"%c", base64EncodingTable[output[i]]]];

        for (i = ctcopy; i < 4; i++)
            [result appendString: @"="];

        ixtext += 3;
        charsonline += 4;

        if ((length > 0) && (charsonline >= length))
            charsonline = 0;
    }     
    return result;
}

@end

然后使用以下语句将其转换为NSString：

NSString *fileStream=[NSString base64StringFromData:imagedata length:[imagedata length] ];

Answer 2

尝试这个

NSString* aStr = [[NSString alloc] initWithData:aData encoding:NSASCIIStringEncoding];

它为我工作。

Answer 3

如果要将数据的原始二进制/十六进制值作为字符串值查看，请执行以下操作：

NSString *hashString = [data.description stringByReplacingOccurrencesOfString:@" " withString:@""];

// Remove brackets < > from the end
hashString = [hashString substringWithRange:NSMakeRange(1, hashString.length-2)];

我之所以使用它，是因为我想验证我的sha512数据值。