将二进制图像数据从Web服务读入UIImage

Question

我正在iPhone应用程序中使用Web服务.Web服务方法返回一个响应,该响应具有多个字段(例如ID,描述等).其中一个字段包含我需要在我的iPhone应用程序中转换为UIImage的二进制图像数据.

我正在成功使用NSXMLParser从XML响应中提取数据.在parser:foundCharacters:XMLParser 的选择器中,它NSString*指向每个字段中的字符串.由于这是一个字符串,这是我在遇到图像字段时读取图像数据的方法:

UIImage *img = [[UIImage alloc] initWithData:[string dataUsingEncoding:NSUTF8StringEncoding]];

但是img变量在这一行之后仍然是"零".似乎XML字符串中的数据与转换不兼容.我在这做错了什么？(我能够将其他字段读入我的变量但不能读取此图像数据字段)

提前致谢..

Answer 1

根据fbrereto的回答,我设法使用以下链接的代码示例将字符串转换为NSData:http://www.cocoadev.com/index.pl？ BaseSixtyFour(滚动到MiloBird用户的代码示例).现在我可以成功构建图像.

它使用objective-c类别将选择器添加+ (id)dataWithBase64EncodedString:(NSString *)string;到NSData类.这是我从上面的链接中提取的必要代码示例:

//MBBase64.h

@interface NSData (MBBase64)

+ (id)dataWithBase64EncodedString:(NSString *)string;     //  Padding '=' characters are optional. Whitespace is ignored.

@end


//MBBase64.m

static const char encodingTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

@implementation NSData (MBBase64)

+ (id)dataWithBase64EncodedString:(NSString *)string;
{
    if (string == nil)
        [NSException raise:NSInvalidArgumentException format:nil];
    if ([string length] == 0)
        return [NSData data];

    static char *decodingTable = NULL;
    if (decodingTable == NULL)
    {
        decodingTable = malloc(256);
        if (decodingTable == NULL)
            return nil;
        memset(decodingTable, CHAR_MAX, 256);
        NSUInteger i;
        for (i = 0; i < 64; i++)
            decodingTable[(short)encodingTable[i]] = i;
    }

    const char *characters = [string cStringUsingEncoding:NSASCIIStringEncoding];
    if (characters == NULL)     //  Not an ASCII string!
        return nil;
    char *bytes = malloc((([string length] + 3) / 4) * 3);
    if (bytes == NULL)
        return nil;
    NSUInteger length = 0;

    NSUInteger i = 0;
    while (YES)
    {
        char buffer[4];
        short bufferLength;
        for (bufferLength = 0; bufferLength < 4; i++)
        {
            if (characters[i] == '\0')
                break;
            if (isspace(characters[i]) || characters[i] == '=')
                continue;
            buffer[bufferLength] = decodingTable[(short)characters[i]];
            if (buffer[bufferLength++] == CHAR_MAX)      //  Illegal character!
            {
                free(bytes);
                return nil;
            }
        }

        if (bufferLength == 0)
            break;
        if (bufferLength == 1)      //  At least two characters are needed to produce one byte!
        {
            free(bytes);
            return nil;
        }

        //  Decode the characters in the buffer to bytes.
        bytes[length++] = (buffer[0] << 2) | (buffer[1] >> 4);
        if (bufferLength > 2)
            bytes[length++] = (buffer[1] << 4) | (buffer[2] >> 2);
        if (bufferLength > 3)
            bytes[length++] = (buffer[2] << 6) | buffer[3];
    }

    realloc(bytes, length);
    return [NSData dataWithBytesNoCopy:bytes length:length];
}

@end

谢谢你们!