A common task for iOS apps is to save data and send it over the network. But before you can do that, you need to convert the data to a suitable format through a process called encoding or serialization. This reverse process is called decoding or deserialization. Download the starter playground using the Download Materials link at the top or bottom of the tutorial. Open Nested types. As you might guess, those two protocols declare that types can be encoded to and decoded from a different format.
The Gifts department gives employees their favorite toys as birthday gifts. Press the blue play button to run the Playground and see the results.
But all of the stored properties of Employee and Toy use camel case only! Fortunately, Foundation has you covered. Open Snake case vs camel case and add the following code just after the encoder and decoder are created, before they get used:. Here, you set keyEncodingStrategy to.
You also set keyDecodingStrategy to.
Run the playground and inspect snakeString. The encoded employee looks like this in this case pun intended :. This means that the field names in the JSON will no longer match up with the property names in your type.
You can define custom coding keys to supply coding names for your properties. You do this by adding a special enum to your type. Open Custom coding keys and add this code inside the Employee type:. CodingKeys is the special enum mentioned above. It conforms to CodingKey and has String raw values. To start, open Keyed containers.
This split is to keep the free member-wise initializer you get with Swift struct s. If you declare an init method in the main definition, you lose that. Add this code inside Employee :.
Run the playground and inspect the value of the encoded string — it will match the JSON at the top of this section. Being able to choose which properties to encode for which keys gives you a lot of flexibility. The decoding process is the opposite of the encoding process.Tag: arraysswifttype-conversionbytebit.
For example I have bits and I should have 35 UInt8 in bytes array. I can think of solution where I take 8bits and check if first is true, if second is true and so and sum the results and have value.
This I would do for every 8bits in my bits array. But I think this would be bad solution it would work but with unnecessary calculations. I think there could be faster solution with some shifting and so but I am really bad in this so I am looking for help. A possible solution is to enumerate all bits in the array and for all "One" bits set the corresponding bit in the UInt8 array:.
Alternatively, you can "inline" the calculation for each group of 8 bits. You'll have to check which solution performs better in your case.
Here, for simplicity, if the number of bits is not a multiple of 8, any excess bits are ignored. The same code can also be written a bit "Swiftier" as. Benchmarks: Here is now a quick-and-dirty benchmarking app code belowcomparing the various solutions. It measures the time to convert 10, bit arrays of length Roll back those changes, add a InfoPlist.
You can find a lot of example for both ways, here's a few: use a GIF for cool background video cover iOS In reply to your Here's what I would do. Its orientation issues. UIImagePickerController wont support landscape mode. You can use :contains selector.
Code Review Stack Exchange is a question and answer site for peer programmer code reviews.Why we get negative value in type casting of int to byte? - Hindi
It only takes a minute to sign up. For decoding binary data in my case, delivered by a Bluetooth deviceI've written this struct:. Given some data buffer, likely containing int s of varying widths packed together, it allows those fields to be read out:. Values in the early data may alter the structure of the later data e. Instead of implementing consume for each integer type separately, you can implement a single generic method:. Another option is to copy the bytes into a value of the desired type instead of bit shifting and adding:.
Instead of letting the compiler infer the return type from the context, one can alternatively pass it as a parameter:. I would probably call the method get or read instead of consume.
Defining a local enum Error type which conforms to the global Error protocol is possible, but might be confusing to the reader. I would use a different name for the concrete error type, for example:. Now let's have a look how an error would be reported. The caller does not know the actual error type, so a typical calling sequence is:. This can be improved by adopting the LocalizedError protocol see for example How to provide a localized description with an Error type in Swift?
Even if you decide not to use it, having a look at its documentation and interface might be instructive. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. A consumable byte array, in Swift Ask Question. Asked 1 year, 10 months ago. Active 1 year, 7 months ago. Viewed 1k times. Would you write the implementation any differently, or change the API?
Chris Chris 4 4 bronze badges. Active Oldest Votes. Int16 bitPattern: buffer. ReadError error 0. Martin R Martin R As you may have noticed, I'd only implemented for the types I'd encountered so far. I think I picked the enum Error: Swift. Error up from swiftbysundell. If there's a neat way of resolving this, it's not apparent to me.
I have updated the answer accordingly.Then: We compare the string returned against the string literal " Note: This String init does not return an optional. It always succeeds, as any Int can be represented in text. This is the opposite conversion. We take a String and try to convert it into an Int. This conversion does not always work. We invoke the Int init and test the result. If let: We use optional binding to extract the Int from the return value an optional.
Info: If no Int exists, the inner statement is not reached. So we can determine when an Int use fails because of an invalid format. This returns an Optional Int. Use optional binding "if let" to get the number.
Some strings cannot be represented as an Int. For example the string XYZ corresponds to no Int. We use Int as before, but handle errors in an else-clause.
Tip: The "if let" syntax offers advantages here.
Get the size of an array
We can access the value if it exists, but also can branch on a parse that fails. In Swift we often use optionals. Here we convert an optional String into a String.
And then we convert the String back into an optional one. Syntax: We use the exclamation mark to access the value in a non-nil optional. We use a question mark to specify an optional container. Handle invalid string data and optionals. No transformation is quite like the butterfly's. Its bright wings emerge from the cocoon. Meanwhile in Swift 4 we transform Strings and Ints. With conversion methods, we can change from Strings to Ints and back again. This is often useful.Convert the UInt8 array back into a String.
String, byte array. In Swift a byte is called a UInt8—an unsigned 8 bit integer. A byte array is a UInt8 array. We can convert his to a byte array. Then we can manipulate bytes. We can convert those bytes into a String. An example. Then it creates a byte array from the UTF8View with an array creation statement.
Next: It changes the first value in the byte array. It increments it, changing "p" to "q. This is a byte array of character data. The byte array is mutable. Create string, bytes. It is possible to create a String from a sequence of bytes. We can specify these directly in the program. This allows dynamic creation of strings.
Here: We create an empty byte array with the UInt8 type. We add 3 UInt8 values to the array. Result: Our resulting string has the value "abc" from the bytes added to the buffer. In Swift, Strings are hard to manipulate. Using a UInt8 array to create certain kinds of strings like those meant for machines is a good strategy to improve performance and gain clarity.
Some notes. In Swift 2 we have access to a utf8 property. This is key to converting Strings to byte arrays. We use the UInt8 type to indicate a byte in this language. Every person is special and unique.
Send bug reports to info dotnetperls.The Swift Sandbox is integrated, making the exercises interactive. Take for example a program where you compute the average of multiple grades in a class:. What if we wanted the program to also work when we have 3 grades? After doing this it will no longer work with 2 grades. What if we wanted our program to work with any number of grades between 1 grade and 10 grades.
We would like to have something like a list of grades.
This list would contain any number of grades. This is where arrays come in. An array is an ordered collection that stores multiple values of the same type.
That means that an array of Int can only store Int values. And you can only insert Int values in it. You can initialize an array with an array literal.
Chapter 6: Arrays
An array literal is a list of values, separated by commas, surrounded by a pair of square brackets:. To get all the values from an array you can use the for-in syntax.
This is called iterating through an array. You can access specific elements from an array using the subscript syntax. To do this pass the index of the value you want to retrieve within square brackets immediately after the name of the array.
Also you can get a subsequence from the array if you pass a range instead of an index. Element in an array are indexed from 0 to the number of elements minus one. So an array with 3 elements will have elements at index 0, 1 and 2. In the example above numbers had 6 elements and after the replacement of the subsequence This means that arrays are copied when they are assigned to a new constant or variable, or when they are passed to a function or method.
If you create an array and assign it to a variable, the collection that is created will be mutable. This means that you can change or mutate the collection after it is created.
Convert an integer array to a byte array
It only takes a minute to sign up. I need the byte representation of a given type, especially doublefloatint8etc. We can use the type inference and get rid of forType type: T.
Typewhich works fine for. What do you think about encapsulating the two function in a class, e. ByteBackPacker and convert them to class functions? What about giving byteOrder: ByteOrder a default value, e. Update: I created a ByteBackpacker project on github. Let me know what you think about it. Using a dedicated enumeration type ByteOrder is a good idea.
If you don't pass the type in the unpack function then the compiler has to infer it from the context and either of these would work:. I think it is a matter of taste which version you choose, I would prefer passing the type explicitly. Encapsulating the functions into a type is also a good idea.
But I would use a struct which is initialized with the byte order, and make that instance methods and not class methods. The reason is that you probably will do several calls with the same byte order and you don't have to pass it to every call:. Your code assumes that the host byte order is little-endian, which is the case for all current OS X and iOS platforms.
On the other hand, Swift is open source now and people already start to port it to different platforms. I have no idea if Swift will be ported to a big-endian platform at some time.
Note that the static property hostByteOrder is computed only once in the lifetime of the app, not each time that it is used. There is — as far as I know — no protocol which comprises all integer and floating point types. What you could do is to define a protocol. I'm working my way through Martin's very useful answer. I have discovered one small simplification. The ByteOrder enum is not required. NSHostByteOrder can be used:. Sign up to join this community.