iOS 数据转换

//int 转data
int i = 1; 
NSData *data = [NSData dataWithBytes: &i length: sizeof(i)]; 
//data 转int
int i; 
[data getBytes: &i length: sizeof(i)]; 

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


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];


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);