1. NSData 与 NSString

1.1 NSData --> NSString

NSString *aString = [[NSString alloc] initWithData:adata encoding:NSUTF8StringEncoding];

1.2 NSString --> NSData

NSString *aString = @"1234";
NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];

2. NSData 与 Byte

2.1 NSData --> Byte

NSString *testString = @"1234567890";
NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];
　　Byte *testByte = (Byte *)[testData bytes];

2.2 Byte --> 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];

3. NSData 与 UIImage

3.1 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 *image = [UIImage imageWithData: imageData];

3.2 UIImage－> NSData

NSData *imageData = UIImagePNGRepresentation(image);

4. NSData 与char

4.1 char * －> NSData

byte *testData =malloc(sizeOf(byte)*16);  
NSData *content =[NSData dataWithBytes:tempData length:16]; 

4.2 NSData －> char *

char *test=(char*)[data bytes]; 

5. byte与NSData

5.1 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 "，testByte[i]）; 

5.2 Byte数组－> NSData

Byte byte[] = {0，1，2，3，4，5，6，7，8，9，10};  
NSData *adata = [[NSData alloc] initWithBytes:byte length:11];  

6. Byte数组与16进制数

6.1 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);  

6.2 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）;