ios开发答疑录系列---(一)Android和IOS图片编码之跨平台传递

============================================================ 博文原创，转载请声明出处电子咖啡(原id蓝岩) ============================================================ 最近需要在IOS盒Android上面进行跨平台的图片传输，需要将图片转换成字符串通过xml进行传输，无奈两个平台有自己独立的图片处理编码机制，因此颇为头疼，

现在已测试成功，与大家分享。

android将图片转换为string代码：

Drawable drawable = res.getDrawable(R.drawable.photo);Bitmap bitmap = ((BitmapDrawable)drawable).getBitmap();ByteArrayOutputStream stream = new ByteArrayOutputStream();bitmap.compress(Bitmap.CompressFormat.JPEG, 100, stream); //---这里是JPEG格式压缩byte[] bitMapData = stream.toByteArray();  String encodedImage = Base64.encodeToString(bitMapData, Base64.DEFAULT);

IOS转换代码，稍微有些复杂，需要为NSData创建category去扩展base64编解码方法。然后调用一下方法。

 UIImage* photo=UIImage imageNamed:@"photo.png"; //--这里是png NSData* photoData=UIImagePNGRepresentation(photo) ; String encodedImage = [photoData base64EncodedString];

有一点我还是不太理解，就是android采用的图片是jpeg，而ios采用的是png，但两者在相互转换编码时候并没有影响，持续研究中........

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附上NSData的base64编解码category

NSData+Base64.h

////  NSData+Base64.h//  base64////  Created by Matt Gallagher on 2009/06/03.//  Copyright 2009 Matt Gallagher. All rights reserved.////  This software is provided 'as-is', without any express or implied//  warranty. In no event will the authors be held liable for any damages//  arising from the use of this software. Permission is granted to anyone to//  use this software for any purpose, including commercial applications, and to//  alter it and redistribute it freely, subject to the following restrictions:////  1. The origin of this software must not be misrepresented; you must not//     claim that you wrote the original software. If you use this software//     in a product, an acknowledgment in the product documentation would be//     appreciated but is not required.//  2. Altered source versions must be plainly marked as such, and must not be//     misrepresented as being the original software.//  3. This notice may not be removed or altered from any source//     distribution.//#import <Foundation/Foundation.h>void *NewBase64Decode(    const char *inputBuffer,    size_t length,    size_t *outputLength);char *NewBase64Encode(    const void *inputBuffer,    size_t length,    bool separateLines,    size_t *outputLength);@interface NSData (Base64)+ (NSData *)dataFromBase64String:(NSString *)aString;- (NSString *)base64EncodedString;@end

NSData+Base64.m：

////  NSData+Base64.m//  base64////  Created by Matt Gallagher on 2009/06/03.//  Copyright 2009 Matt Gallagher. All rights reserved.////  This software is provided 'as-is', without any express or implied//  warranty. In no event will the authors be held liable for any damages//  arising from the use of this software. Permission is granted to anyone to//  use this software for any purpose, including commercial applications, and to//  alter it and redistribute it freely, subject to the following restrictions:////  1. The origin of this software must not be misrepresented; you must not//     claim that you wrote the original software. If you use this software//     in a product, an acknowledgment in the product documentation would be//     appreciated but is not required.//  2. Altered source versions must be plainly marked as such, and must not be//     misrepresented as being the original software.//  3. This notice may not be removed or altered from any source//     distribution.////  Comments converted to be ARC compatible#import "NSData+Base64.h"//// Mapping from 6 bit pattern to ASCII character.//static unsigned char base64EncodeLookup[65] =    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";//// Definition for "masked-out" areas of the base64DecodeLookup mapping//#define xx 65//// Mapping from ASCII character to 6 bit pattern.//static unsigned char base64DecodeLookup[256] ={    xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, 62, xx, xx, xx, 63,     52, 53, 54, 55, 56, 57, 58, 59, 60, 61, xx, xx, xx, xx, xx, xx,     xx,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,     15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, xx, xx, xx, xx, xx,     xx, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,     41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx,     xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, };//// Fundamental sizes of the binary and base64 encode/decode units in bytes//#define BINARY_UNIT_SIZE 3#define BASE64_UNIT_SIZE 4//// NewBase64Decode//// Decodes the base64 ASCII string in the inputBuffer to a newly malloced// output buffer.////  inputBuffer - the source ASCII string for the decode//  length - the length of the string or -1 (to specify strlen should be used)//  outputLength - if not-NULL, on output will contain the decoded length//// returns the decoded buffer. Must be free'd by caller. Length is given by//  outputLength.//void *NewBase64Decode(    const char *inputBuffer,    size_t length,    size_t *outputLength){    if (length == -1)    {        length = strlen(inputBuffer);    }        size_t outputBufferSize =        ((length+BASE64_UNIT_SIZE-1) / BASE64_UNIT_SIZE) * BINARY_UNIT_SIZE;    unsigned char *outputBuffer = (unsigned char *)malloc(outputBufferSize);        size_t i = 0;    size_t j = 0;    while (i < length)    {        //        // Accumulate 4 valid characters (ignore everything else)        //        unsigned char accumulated[BASE64_UNIT_SIZE];        size_t accumulateIndex = 0;        while (i < length)        {            unsigned char decode = base64DecodeLookup[inputBuffer[i++]];            if (decode != xx)            {                accumulated[accumulateIndex] = decode;                accumulateIndex++;                                if (accumulateIndex == BASE64_UNIT_SIZE)                {                    break;                }            }        }                //        // Store the 6 bits from each of the 4 characters as 3 bytes        //        // (Uses improved bounds checking suggested by Alexandre Colucci)        //        if(accumulateIndex >= 2)              outputBuffer[j] = (accumulated[0] << 2) | (accumulated[1] >> 4);          if(accumulateIndex >= 3)              outputBuffer[j + 1] = (accumulated[1] << 4) | (accumulated[2] >> 2);          if(accumulateIndex >= 4)              outputBuffer[j + 2] = (accumulated[2] << 6) | accumulated[3];        j += accumulateIndex - 1;    }        if (outputLength)    {        *outputLength = j;    }    return outputBuffer;}//// NewBase64Encode//// Encodes the arbitrary data in the inputBuffer as base64 into a newly malloced// output buffer.////  inputBuffer - the source data for the encode//  length - the length of the input in bytes//  separateLines - if zero, no CR/LF characters will be added. Otherwise//      a CR/LF pair will be added every 64 encoded chars.//  outputLength - if not-NULL, on output will contain the encoded length//      (not including terminating 0 char)//// returns the encoded buffer. Must be free'd by caller. Length is given by//  outputLength.//char *NewBase64Encode(    const void *buffer,    size_t length,    bool separateLines,    size_t *outputLength){    const unsigned char *inputBuffer = (const unsigned char *)buffer;        #define MAX_NUM_PADDING_CHARS 2    #define OUTPUT_LINE_LENGTH 64    #define INPUT_LINE_LENGTH ((OUTPUT_LINE_LENGTH / BASE64_UNIT_SIZE) * BINARY_UNIT_SIZE)    #define CR_LF_SIZE 2        //    // Byte accurate calculation of final buffer size    //    size_t outputBufferSize =            ((length / BINARY_UNIT_SIZE)                + ((length % BINARY_UNIT_SIZE) ? 1 : 0))                    * BASE64_UNIT_SIZE;    if (separateLines)    {        outputBufferSize +=            (outputBufferSize / OUTPUT_LINE_LENGTH) * CR_LF_SIZE;    }        //    // Include space for a terminating zero    //    outputBufferSize += 1;    //    // Allocate the output buffer    //    char *outputBuffer = (char *)malloc(outputBufferSize);    if (!outputBuffer)    {        return NULL;    }    size_t i = 0;    size_t j = 0;    const size_t lineLength = separateLines ? INPUT_LINE_LENGTH : length;    size_t lineEnd = lineLength;        while (true)    {        if (lineEnd > length)        {            lineEnd = length;        }        for (; i + BINARY_UNIT_SIZE - 1 < lineEnd; i += BINARY_UNIT_SIZE)        {            //            // Inner loop: turn 48 bytes into 64 base64 characters            //            outputBuffer[j++] = base64EncodeLookup[(inputBuffer[i] & 0xFC) >> 2];            outputBuffer[j++] = base64EncodeLookup[((inputBuffer[i] & 0x03) << 4)                | ((inputBuffer[i + 1] & 0xF0) >> 4)];            outputBuffer[j++] = base64EncodeLookup[((inputBuffer[i + 1] & 0x0F) << 2)                | ((inputBuffer[i + 2] & 0xC0) >> 6)];            outputBuffer[j++] = base64EncodeLookup[inputBuffer[i + 2] & 0x3F];        }                if (lineEnd == length)        {            break;        }                //        // Add the newline        //        outputBuffer[j++] = '\r';        outputBuffer[j++] = '\n';        lineEnd += lineLength;    }        if (i + 1 < length)    {        //        // Handle the single '=' case        //        outputBuffer[j++] = base64EncodeLookup[(inputBuffer[i] & 0xFC) >> 2];        outputBuffer[j++] = base64EncodeLookup[((inputBuffer[i] & 0x03) << 4)            | ((inputBuffer[i + 1] & 0xF0) >> 4)];        outputBuffer[j++] = base64EncodeLookup[(inputBuffer[i + 1] & 0x0F) << 2];        outputBuffer[j++] = '=';    }    else if (i < length)    {        //        // Handle the double '=' case        //        outputBuffer[j++] = base64EncodeLookup[(inputBuffer[i] & 0xFC) >> 2];        outputBuffer[j++] = base64EncodeLookup[(inputBuffer[i] & 0x03) << 4];        outputBuffer[j++] = '=';        outputBuffer[j++] = '=';    }    outputBuffer[j] = 0;        //    // Set the output length and return the buffer    //    if (outputLength)    {        *outputLength = j;    }    return outputBuffer;}@implementation NSData (Base64)//// dataFromBase64String://// Creates an NSData object containing the base64 decoded representation of// the base64 string 'aString'//// Parameters://    aString - the base64 string to decode//// returns the NSData representation of the base64 string//+ (NSData *)dataFromBase64String:(NSString *)aString{    NSData *data = [aString dataUsingEncoding:NSASCIIStringEncoding];    size_t outputLength;    void *outputBuffer = NewBase64Decode([data bytes], [data length], &outputLength);    NSData *result = [NSData dataWithBytes:outputBuffer length:outputLength];    free(outputBuffer);    return result;}//// base64EncodedString//// Creates an NSString object that contains the base 64 encoding of the// receiver's data. Lines are broken at 64 characters long.//// returns an NSString being the base 64 representation of the//  receiver.//- (NSString *)base64EncodedString{    size_t outputLength;    char *outputBuffer =        NewBase64Encode([self bytes], [self length], true, &outputLength);        NSString *result =        [[NSString alloc] initWithBytes:outputBuffer length:outputLength encoding:NSASCIIStringEncoding];    free(outputBuffer);    return result;}@end

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