NSData與NSString、NSData與UIImage的數據類型轉換

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 UIImage
NSData --> UIImage
　　UIImage *aimage = [UIImage imageWithData: imageData];
　　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);