NSData各種轉(zhuǎn)換
http://blog.csdn.net/bailu66/article/details/7665357

1，NSData 與 NSString
　　
NSData --> NSString
　　
NSString *aString = [[NSString alloc] initWithData:adata encoding:NSUTF8StringEncoding];
NSString --> NSData
　　
NSString *aString = @"1234";
NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];

2，NSData 與 Byte
　　
NSData --> Byte
　　
NSString *testString = @"1234567890";
NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];
Byte *testByte = (Byte *)[testData bytes];
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 與 UIImage
　　NSData --> UIImage
　　UIImage *aimage = [UIImage imageWithData: imageData];
　　//例：從本地文件沙盒中取圖片并轉(zhuǎn)換為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);

4，NSData 與 NSMutableData
　　NSData --> MSMutableData
　　NSData *data=[[NSData alloc]init];
　　NSMutableData *mdata=[[NSMutableData alloc]init];
　　mdata=[NSData dataWithData:data];