以字符串格式保存图像(以在xml中使用)..不起作用 [英] saving images in string format (to use in xml)..not working

问题描述

我正在将图像从选择器转换为nsdata(jpeg表示形式)，然后使用以下代码将其转换为nsstring

i am converting image from picker into nsdata(jpeg representation) and then converting it into nsstring using the following code

 NSData *data=UIImageJPEGRepresentation(image,1.0);
 NSString *imageString=[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
[[NSUserDefaults standardUserDefaults] setObject:imageString forKey:@"image_name"];

在需要显示图像的另一端，uiimage如下形成.

and at the other end where i need to display the image the uiimage is formed as follows.

 NSString *imageString=[[NSString alloc] init];
 imageString=[[NSUserDefaults standardUserDefaults] objectForKey:@"image_name"];
 UIImage *image=[UIImage imageWithData:[imageString dataUsingEncoding:NSUTF8StringEncoding]];

在最上面的代码中使用的image变量不是nil，但是由数据形成的图像正在nil ...当我nslogging userdefaults时，上述键存在一些字符串.任何人都可以解释为什么会这样.什么是正确的方法

the image variable used in the top code is not nil ,but the image formed from data is getting nil...when i nslogged userdefaults some string is present for the key mentioned above .can anyone explain why is this so..what is the right way to do this

推荐答案

如果它通过Web服务器或类似服务器，则可以使用base64 enc/decoding或其他一些普通编码器对其进行封装.

If it goes through a web server or the like, you could encapsulate it with base64 enc/decoding or some other plain encoder.

它删除坏"字符，即在转换过程中拧紧字符串，然后将其更改为通用字母字符，然后再次返回.

It removes "bad" char, ie that screw up the string during transformation, and change them to generic alphabetical chars and then back again.

如果这是导致您遇到问题的原因，那么请使用以下简短内容(我很可能是偷来的并改编了，但不记得是从谁那里来的.抱歉！:-))

if this is the reason to your issues, here is a short one i use (which I most probably stole and adapted, but do not remember from whom. Sorry! :-) )

base64helper.h

base64helper.h

    #import <Foundation/Foundation.h>
    @interface NSData (MBBase64)

base64helper.m

base64helper.m

#import "base64helper.h"

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];
}

- (NSString *)base64Encoding;
{
    if ([self length] == 0)
        return @"";

    char *characters = malloc((([self length] + 2) / 3) * 4);
    if (characters == NULL)
        return nil;
    NSUInteger length = 0;

    NSUInteger i = 0;
    while (i < [self length])
    {
        char buffer[3] = {0,0,0};
        short bufferLength = 0;
        while (bufferLength < 3 && i < [self length])
            buffer[bufferLength++] = ((char *)[self bytes])[i++];

        //  Encode the bytes in the buffer to four characters, including padding "=" characters if necessary.
        characters[length++] = encodingTable[(buffer[0] & 0xFC) >> 2];
        characters[length++] = encodingTable[((buffer[0] & 0x03) << 4) | ((buffer[1] & 0xF0) >> 4)];
        if (bufferLength > 1)
            characters[length++] = encodingTable[((buffer[1] & 0x0F) << 2) | ((buffer[2] & 0xC0) >> 6)];
        else characters[length++] = '=';
        if (bufferLength > 2)
            characters[length++] = encodingTable[buffer[2] & 0x3F];
        else characters[length++] = '=';    
    }

    return [[[NSString alloc] initWithBytesNoCopy:characters length:length encoding:NSASCIIStringEncoding freeWhenDone:YES] autorelease];
}
@end

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