NSData各种转换
http://blog.csdn.net/bailu66/article/details/7665357
1，NSData 与 NSString
NSData --> NSString
NSString *aString = [[NSString alloc] initWithData:adata encoding:NSUTF8StringEncoding];
NSString --> NSData
NSString *aString = @"1234";
NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];
2，NSData 与 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 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);
4，NSData 与 NSMutableData
NSData --> MSMutableData
NSData *data=[[NSData alloc]init];
NSMutableData *mdata=[[NSMutableData alloc]init];
mdata=[NSData dataWithData:data];
