How to save UIImage as PNG

saveImageFile

- (void)saveImageFile
{
        NSData *data = UIImagePNGRepresentation(uiimage);
        NSString *filePath = [NSString stringWithFormat:@"%@/sample.png" ,[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"]];
        [data writeToFile:filePath atomically:YES];
}