Encoding/decoding arbitrary binary data to string in swift/objective-c

Question

I need to encode/decode an arbitrary NSData object into a String/NSString. Here's what I have for encoding:

    var avatar64 = self.avatar.base64EncodedStringWithOptions(NSDataBase64EncodingOptions.fromRaw(0)!);
    let avatarData = NSData(base64EncodedString: avatar64, options: NSDataBase64DecodingOptions.fromRaw(0)!);
    let avatar = NSString(data: avatarData, encoding: NSUTF8StringEncoding);

But avatar is nil. What am I doing wrong?

Martin R · Accepted Answer · 2014-07-10 14:21:31Z

3

Your first step already creates a Base64-encoded string of the data in self.avatar:

var avatar64 = self.avatar.base64EncodedStringWithOptions(NSDataBase64EncodingOptions.fromRaw(0)!);

Your second step decodes the Base64 string again, so that avatarData contains the same binary data as your original self.avatar:

let avatarData = NSData(base64EncodedString: avatar64, options: NSDataBase64DecodingOptions.fromRaw(0)!);

Finally, your third step tries to create a string from the original (binary) data:

let avatar = NSString(data: avatarData, encoding: NSUTF8StringEncoding);

This fails because the data is not a valid UTF-8 sequence.

In short: Just remove the third and second line.

answered Jul 10, 2014 at 14:21

Martin R

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6 Comments

André Fratelli Over a year ago

That's what I had to begin with... I ended up adding to it because it was failing somewhere else. I guess I was wrong to do it. I'll file another question. Thank you.

Programming Learner Over a year ago

Hi, I have stucked in same kind of situation. I make creating a UIImage like , var image: UIImage = UIImage(named:"one12.png"). Then I am converting the image to NSData like,var data1:NSData = UIImagePNGRepresentation(image), Now I am converting the NSData back to String like, let base64String = data1.base64EncodedStringWithOptions(NSDataBase64EncodingOptions.fromRaw(0)!) as String. Now I am paasing the image as parameter to the server like, var params = ["username":"json", "password":"iosi","profile_img":base64String]as NSDictionary . What I am doing wrong? Please explain me.

Ankita Shah Over a year ago

@Annu How did you solve this. I'm also stuck with the similar issue. Sometime image is passed properly and sometime it does not.

Programming Learner Over a year ago

@Ankita Sorry, but I still haven't implemented this. Actually I was trying to implement this one in a demo project. I'll post the answer when I'll implement.

Ankita Shah Over a year ago

@Annu, Thanks for your reply. My issue is solved now. Before request was as URLRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type"), then I added URLRequest.setValue("application/json", forHTTPHeaderField: "Content-Type") URLRequest.setValue("application/json", forHTTPHeaderField: "Accept"). As we are passing json data so we can directly set content type like this rather then using form encoding

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