NSData－> NSString    NSString *aString = [[NSString alloc] initWithData:adataencoding:NSUTF8StringEncoding];         NSString－>NSData    NSString *aString = @"1234abcd";    NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];         2.NSData 与 Byte    NSData－> Byte数组    NSString *testString = @"1234567890";    NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];    Byte *testByte = (Byte *)[testData bytes];    for(int i=0;i<[testData length];i++)    printf("testByte = %d\n",testByte[i]);         Byte数组－> NSData    Byte byte[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23};    NSData *adata = [[NSData alloc] initWithBytes:byte length:24];         Byte数组－>16进制数    Byte *bytes = (Byte *)[aData bytes];    NSString *hexStr=@"";    for(int i=0;i<[encryData length];i++)    {    NSString *newHexStr = [NSString stringWithFormat:@"%x",bytes[i]&0xff];///16进制数    if([newHexStr length]==1)    hexStr = [NSString stringWithFormat:@"%@0%@",hexStr,newHexStr];    else     hexStr = [NSString stringWithFormat:@"%@%@",hexStr,newHexStr];    }    NSLog(@"bytes 的16进制数为:%@",hexStr);         16进制数－>Byte数组    ///// 将16进制数据转化成Byte 数组    NSString *hexString = @"3e435fab9c34891f"; //16进制字符串    int j=0;    Byte bytes[128];  ///3ds key的Byte 数组， 128位    for(int i=0;i<[hexString length];i++)    {    int int_ch;  /// 两位16进制数转化后的10进制数         unichar hex_char1 = [hexString characterAtIndex:i]; ////两位16进制数中的第一位(高位*16)    int int_ch1;    if(hex_char1 >= '0' && hex_char1 <='9')    int_ch1 = (hex_char1-48)*16;   //// 0 的Ascll - 48    else if(hex_char1 >= 'A' && hex_char1 <='F')    int_ch1 = (hex_char1-55)*16; //// A 的Ascll - 65    else     int_ch1 = (hex_char1-87)*16; //// a 的Ascll - 97    i++;         unichar hex_char2 = [hexString characterAtIndex:i]; ///两位16进制数中的第二位(低位)    int int_ch2;    if(hex_char2 >= '0' && hex_char2 <='9')    int_ch2 = (hex_char2-48); //// 0 的Ascll - 48    else if(hex_char1 >= 'A' && hex_char1 <='F')    int_ch2 = hex_char2-55; //// A 的Ascll - 65    else     int_ch2 = hex_char2-87; //// a 的Ascll - 97         int_ch = int_ch1+int_ch2;    NSLog(@"int_ch=%d",int_ch);    bytes[j] = int_ch;  ///将转化后的数放入Byte数组里    j++;    }    NSData *newData = [[NSData alloc] initWithBytes:bytes length:128];    NSLog(@"newData=%@",newData);         3. NSData 与 UIImage    NSData－>UIImage    UIImage *aimage = [UIImage imageWithData: imageData];         //例：从本地文件沙盒中取图片并转换为NSData    NSString *path = [[NSBundle mainBundle] bundlePath];    NSString *name = [NSString stringWithFormat:@"ceshi.png"];    NSString *finalPath = [path stringByAppendingPathComponent:name];    NSData *imageData = [NSData dataWithContentsOfFile: finalPath];    UIImage *aimage = [UIImage imageWithData: imageData];         UIImage－> NSData    NSData *imageData = UIImagePNGRepresentation(aimae);