The following Swift code (writing bytes to a stream) is rewritten from Objective-C:
var outputStream : NSOutputStream = NSOutputStream()
var pData : NSMutableData = NSMutableData()
var pType : Int = 1
let pMessage : String = "Device_Description\0\0\x01" // 16BitChar with escapeSequence
var pLength : Int = 8+pMessage.lengthOfBytesUsingEncoding(NSUTF16LittleEndianStringEncoding)
pData.appendBytes(&pLength, length: 4)
pData.appendBytes(&pType, length: 4)
pData.appendData((pMessage as NSString).dataUsingEncoding(NSUTF16LittleEndianStringEncoding))
outputStream.write(pData.bytes, maxLength: pData.length)
pData.bytes is of type COpaquePointer, but CConstPointer<Uint8>is needed by the write operation. Any hints for the correct conversion? Thanks in advance.
As Jack wu has outlined, but somewhat incompletely, the following code works just the same as using the UnsafePointer option:
var byteData = [UInt8]()
pData.getBytes(&byteData)
self.outputStream!.write(byteData, maxLength: pData.length)
From the Swift & Objc interop book section here : https://developer.apple.com/library/prerelease/ios/documentation/swift/conceptual/buildingcocoaapps/InteractingWithCAPIs.html
C Constant Pointers
When a function is declared as taking a CConstPointer argument,
it can accept any of the following:
nil, which is passed as a null pointer
A CMutablePointer, CMutableVoidPointer, CConstPointer, CConstVoidPointer, or AutoreleasingUnsafePointer value, which
is converted to CConstPointer if necessary
An in-out expression whose operand is an lvalue of type Type, which is passed as the address of the lvalue
A Type[] value, which is passed as a pointer to the start of the array, and lifetime-extended for the duration of the call
I believe then it can work like this:
var p: [Uint8] = []
pData.getBytes(&p)
outputStream.write(p, maxLength: pData.length)
I found a simple solution right now, by use of UnsafePointer<T>():
var outputStream : NSOutputStream = NSOutputStream()
var pData : NSMutableData = NSMutableData()
var pType : Int = 1
let pMessage : String = "Device_Description\0\0\x01" // 16BitChar with escapeSequence
var pLength : Int = 8+pMessage.lengthOfBytesUsingEncoding(NSUTF16LittleEndianStringEncoding)
pData.appendBytes(&pLength, length: 4)
pData.appendBytes(&pType, length: 4)
pData.appendData(ptpMessage.dataUsingEncoding(NSUTF16LittleEndianStringEncoding))
outputStream.write(UnsafePointer<UInt8>(pData.bytes), maxLength: pData.length)
#holex: Thanks for your input. I know this solution is not quite Swifty, but it´s working for now.
Related
I have explained my query in the code snippet below. I am looking for this type of syntax for Obj-C interoperability. Specifically I see a difference in behaviour of aCoder.encode(count, forKey: "count") API when count is Int (non-optional) vs Int? (optional)
import Foundation
let num = 5
// Swift's type system will infer this as Int (non-optional)
print(type(of: num))
// Prints: Int
let optNum: Int? = 5
// This is explicitly typed as an optional Int
print(type(of: optNum))
// Prints Optional<Int>
Is it possible to use a literal to implicitly type a var/let to optional?
// let imlicitOptional = 5?
// print(type(of: imlicitOptional))
// The above line should print: Optional<Int>
// or
// let imlicitOptional = num?
// print(type(of: imlicitOptional))
// The above line should print: Optional<Int>
Optional is a plain enum not any specific magic type. So, you can create a value using Optional:
let implicitOptional = Optional(5)
print(type(of: implicitOptional)) // Optional<Int>
I don't know why you need this but you can do like this
let opt = 5 as Int?
// or
let opt = Optional(5)
// or
let opt = 5 as Optional // thanks to vacawama for this
Actually you can even create an operator that returns an optional but I think it's kinda useless.
postfix operator >?
postfix func >?<T>(value: T) -> T? {
return Optional(value) // or return value as T?
}
let a = 5>?
I don't undertand how to specify the default value for `ByteArray.getOrElse() function.
I tried:
myInt = dat.getOrElse(0, 0).toInt()
but compiler complains with the following error:
The integer literal does not conform to the expected type (Int) -> Byte
How to specify the default value?
The expected type of the second argument (defaultValue) is (Int) -> Byte which is a lambda that takes an Int and returns a Byte.
myInt = dat.getOrElse(index = 100, defaultValue = {
i ->
// use i to calcuate your Byte that should be returned...
// or return a fixed value
i * 1 // for example
})
Signature of getOrElse:
fun ByteArray.getOrElse(
index: Int,
defaultValue: (Int) -> Byte
): Byte
The second argument is a function literal
myInt = dat.getOrElse(100, { /** what is there is no element 100*/ 0 })
I have the following code written in Objective-C:
int port1 = SERVER_DEVICE_PORT;
int port2 = SERVER_DEVICE_PORT>>8;
Byte port1Byte[1] = {port1};
Byte port2Byte[1] = {port2};
NSData *port1Data = [[NSData alloc]initWithBytes: port1Byte length: sizeof(port1Byte)];
NSData *port2Data = [[NSData alloc]initWithBytes: port2Byte length: sizeof(port2Byte)];
I have converted it to Swift 3 like so:
let port1: Int = Int(SERVER_DEVICE_PORT)
let port2: Int = Int(SERVER_DEVICE_PORT) >> 8
let port1Bytes: [UInt8] = [UInt8(port1)]
let port2Bytes: [UInt8] = [UInt8(port2)]
let port1Data = NSData(bytes: port1Bytes, length: port1)
let port2Data = NSData(bytes: port2Bytes, length: port2)
However, with this code I am receiving the following error:
How can this be fixed?
The easiest way in Swift 3 to get the two lowest bytes from a 32 bit value is
var SERVER_DEVICE_PORT : Int32 = 55056
let data = Data(buffer: UnsafeBufferPointer(start: &SERVER_DEVICE_PORT, count: 1))
// or let data = Data(bytes: &SERVER_DEVICE_PORT, count: 2)
let port1Data = data[0]
let port2Data = data[1]
print(port1Data, port2Data)
This results UInt8 values, to get Data use
let port1Data = Data([data[0]])
let port2Data = Data([data[1]])
If – for some reason – the 32bit value is big endian (most significant byte in the smallest address) then port1Data = data[3] and port2Data = data[2].
I am getting the error Type 'CUnsignedChar?' has no subscript members which produces a lot of results in stackoverflow however I can't seem to utilise any of the other available answers for my example. Its clearly a casting issue but I don't not see how to overcome it
I am doing a obj-c to swift conversion and I have a variable being set up as follows
var bBuff1 = [CUnsignedChar](repeating: 0, count: Int(256*512))
var backGreyBuffer : CUnsignedChar = bBuff1[0]
//..
//..
var backGreyBufferOffset : Int = localTexOffset * 512
var grey_val = 0
self.backGreyBuffer[Int(backGreyBufferOffset)]! = grey_val; //Subscript error here
This is the obj-c code that uses in-outs.
unsigned char bBuff1[256*512];
unsigned char *backGreyBuffer = &bBuff1[0];
//..
grey_val = 0;
backGreyBuffer[backGreyBufferOffset] = grey_val;
Any suggestions about the right direction would be great.
I noticed that only a small change is needed in your code. You should make backGreyBuffer a pointer:
var bBuff1 = [CUnsignedChar](repeating: 0, count: Int(256*512))
var backGreyBuffer = UnsafeMutablePointer(mutating: bBuff1)
// ....
var backGreyBufferOffset = localTexOffset * 512
backGreyBuffer[backGreyBufferOffset] = grey_val
I was pointed to this objc snippet from WWDC 14, but I work on a Swift project.
CMIOObjectPropertyAddress prop = {
kCMIOHardwarePropertyAllowScreenCaptureDevices,
kCMIOObjectPropertyScopeGlobal,
kCMIOObjectPropertyElementMaster
};
UInt32 allow = 1;
CMIOObjectSetPropertyData(kCMIOObjectSystemObject, &prop, 0, NULL, sizeof(allow), &allow);
I then tried rewriting to Swift:
var prop : CMIOObjectPropertyAddress {
kCMIOHardwarePropertyAllowScreenCaptureDevices
kCMIOObjectPropertyScopeGlobal
kCMIOObjectPropertyElementMaster
}
var allow:UInt32 = 1
CMIOObjectSetPropertyData(kCMIOObjectSystemObject, &prop, 0, nil, sizeof(UInt32), &allow)
But it doesn't even validate. I don't know how to translate the CMIOObjectPropertyAddress struct. Xcode says
/Users/mortenjust/Dropbox/hack/learning/screenrec/screenrec/deleteme.swift:32:61:
Cannot assign to a get-only property 'prop'
A C struct translates as a Swift struct. Use the implicit memberwise initializer:
var prop = CMIOObjectPropertyAddress(
mSelector: UInt32(kCMIOHardwarePropertyAllowScreenCaptureDevices),
mScope: UInt32(kCMIOObjectPropertyScopeGlobal),
mElement: UInt32(kCMIOObjectPropertyElementMaster))
The cool part is when you type CMIOObjectPropertyAddress(, code completion gives you the rest.
You're right, just got it running right this second. Turns out I also had to correct for some of the types. Here's the complete translation:
var prop = CMIOObjectPropertyAddress(
mSelector: CMIOObjectPropertySelector(kCMIOHardwarePropertyAllowScreenCaptureDevices),
mScope: CMIOObjectPropertyScope(kCMIOObjectPropertyScopeGlobal),
mElement: CMIOObjectPropertyElement(kCMIOObjectPropertyElementMaster))
var allow : UInt32 = 1
var dataSize : UInt32 = 4
var zero : UInt32 = 0
CMIOObjectSetPropertyData(CMIOObjectID(kCMIOObjectSystemObject), &prop, zero, nil, dataSize, &allow)
var session = AVCaptureSession()
session.sessionPreset = AVCaptureSessionPresetHigh
var devices = AVCaptureDevice.devices()
for device in AVCaptureDevice.devices() {
println(device)
}