Base64把图片、文件转码成字符串（互转）

文件Base64以后会翻倍的涨，例如一张52kb的图片 base64以后string文件大小为185kb，在通过string转回图片为135kb

图片转文字：

UIImage *_originImage = [UIImage imageNamed:@"0.jpg"];

NSData *_data = UIImageJPEGRepresentation(_originImage, 1.0f);

NSString *_encodedImageStr = [_data base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
[_encodedImageStr writeToFile:@"/Users/Singer/Documents/0.txt" atomically:YES encoding:NSUTF8StringEncoding error:nil];

NSLog(@"===Encoded image:\n%@", _encodedImageStr);

文字转图片：

NSString *imageStr = [NSString stringWithContentsOfFile:@"/Users/Singer/Documents/0.txt" encoding:NSUTF8StringEncoding error:nil];
NSData *d = [[NSData alloc]initWithBase64EncodedString:imageStr options:NSDataBase64DecodingIgnoreUnknownCharacters];
UIImage *image = [UIImage imageWithData:d];

UIImageView *imageView = [[UIImageView alloc]initWithFrame:CGRectMake(50, 50, 200, 200)];
imageView.image = image;
[self.view addSubview:imageView];
[d writeToFile:@"/Users/Singer/Documents/1111.jpg" atomically:YES];