How To Make Your Websites Faster On Mobile Devices

With the release of iOS 7, Apple added support for encoding and decoding data using Base64. In this post we will walk through two examples using Base64 to encode and decode both NSData and NSString objects.

First, we will create an NSString object that is generated by Base64 encoding an NSData object. This will be followed by decoding the Base64 NSString back into an NSData object. We will display the NSString data, both encoded and decoded to make sure all is well.

The second example will encode and decode NSData to/from Base64. This example is relevant if you have an NSData object that needs to be Base64 encoded, or you need to decode a Base64 NSData object (for whatever reason).

Create a Base64 Encoded NSString Object

Let’s begin by encoding an NSData object into Base64 and returning an NSString object:

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// Create NSData objectNSData *nsdata = [@"iOS Developer Tips encoded in Base64"  dataUsingEncoding:NSUTF8StringEncoding]; // Get NSString from NSData object in Base64NSString *base64Encoded = [nsdata base64EncodedStringWithOptions:0]; // Print the Base64 encoded stringNSLog(@"Encoded: %@", base64Encoded); // Let's go the other way... // NSData from the Base64 encoded strNSData *nsdataFromBase64String = [[NSData alloc]  initWithBase64EncodedString:base64Encoded options:0]; // Decoded NSString from the NSDataNSString *base64Decoded = [[NSString alloc]   initWithData:nsdataFromBase64String encoding:NSUTF8StringEncoding];NSLog(@"Decoded: %@", base64Decoded);

On line 2 we create the NSData to encode. Line 6 encodes the data and returns an NSString object.

To go back the other way, from a Base64 encoded NSString object to an NSData object is as easy as calling the methodinitWithBase64EncodedString, passing in the Base64 encoded NSString (lines 14-15).

Lines 18-20 go from the Base64 NSData object back to an NSString (which is how we started this example, from a string).

The output looks as follows:

Encoded: aU9TIERldmVsb3BlciBUaXBzIGVuY29kZWQgaW4gQmFzZTY0Decoded: iOS Developer Tips encoded in Base64

Base64 Encode an NSData Object

There’s a good chance the NSString conversions (above) may be more about debugging than a day-to-day need to Base64 encoded strings. With that in mind, let’s look at how to directly encode an NSData object to Base64 as well as how to decode an NSData object from Base64.

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// Create NSData objectNSData *dataTake2 =   [@"iOS Developer Tips" dataUsingEncoding:NSUTF8StringEncoding]; // Convert to Base64 dataNSData *base64Data = [dataTake2 base64EncodedDataWithOptions:0];NSLog(@"%@", [NSString stringWithUTF8String:[base64Data bytes]]); // Do something with the data// ... // Now convert back from Base64NSData *nsdataDecoded = [base64Data initWithBase64EncodedData:base64Data options:0];NSString *str = [[NSString alloc] initWithData:nsdataDecoded encoding:NSUTF8StringEncoding];NSLog(@"%@", str);

On line 2 we create our NSData test subject. Line 6 we call the base64EncodedDataWithOptions method of the NSData class to Base64 encode the data. I’ve included an NSString conversion of the data solely to verify what goes in is the same as what comes back out.

Decoding the Base64 NSData object is nothing more than calling the method initWithBase64EncodedData with the encoded NSData object (line 13). Once again, I’ve included an NSString conversion for testing.

Additional Reading

• The NSData class reference includes the information on how to encode and decode NSData using Base64.
• The NSString class reference explains the nuances of encoding and decoding when working with NSString objects.
• I’ve found that encoding and decoding data from the terminal can be helpful when debugging. This Mac OS X doc describes thebase64 OS X terminal utility.