Swift中的免费桥接和指针访问

Question

我正在将一个应用程序从Objective移植到Swift，我需要使用以下方法：

CFStreamCreatePairWithSocketToHost(alloc: CFAllocator!, host: CFString!, port: UInt32, \
readStream: CMutablePointer<Unmanaged<CFReadStream>?>, \
writeStream: CMutablePointer<Unmanaged<CFWriteStream>?>)

旧的逻辑看起来是这样的(几个网站似乎都同意这个逻辑)：

CFReadStreamRef readStream = NULL;
CFWriteStreamRef writeStream = NULL;
CFStreamCreatePairWithSocketToHost(NULL, (__bridge CFStringRef)(host), port, \
                                   &readStream, &writeStream);

NSInputStream inputStream = (__bridge_transfer NSInputStream *)readStream;
NSOutputStream outputStream = (__bridge_transfer NSOutputStream *)writeStream;

这很好，多亏了免费桥接。然而，ARC并不存在于“Swift空间”中，而且这种类型的系统已经发生了变化。

如何将我的流转换为

CMutablePointer<Unmanaged<CFReadStream>?>, and
CMutablePointer<Unmanaged<CFWriteStream>?>

然后在调用NSStream之后将它们转换回CFStreamCreatePairWithSocketToHost子类？

Answer 1

我已经开始工作了，下面是我的代码:确保在某个地方保存一个连接类的引用:-)

class Connection : NSObject, NSStreamDelegate {
    let serverAddress: CFString = "127.0.0.1"
    let serverPort: UInt32 = 8443

    private var inputStream: NSInputStream!
    private var outputStream: NSOutputStream!

    func connect() {
        println("connecting...")

        var readStream:  Unmanaged<CFReadStream>?
        var writeStream: Unmanaged<CFWriteStream>?

        CFStreamCreatePairWithSocketToHost(nil, self.serverAddress, self.serverPort, &readStream, &writeStream)

        // Documentation suggests readStream and writeStream can be assumed to
        // be non-nil. If you believe otherwise, you can test if either is nil
        // and implement whatever error-handling you wish.

        self.inputStream = readStream!.takeRetainedValue()
        self.outputStream = writeStream!.takeRetainedValue()

        self.inputStream.delegate = self
        self.outputStream.delegate = self

        self.inputStream.scheduleInRunLoop(NSRunLoop.currentRunLoop(), forMode: NSDefaultRunLoopMode)
        self.outputStream.scheduleInRunLoop(NSRunLoop.currentRunLoop(), forMode: NSDefaultRunLoopMode)

        self.inputStream.open()
        self.outputStream.open()
    }

    func stream(stream: NSStream, handleEvent eventCode: NSStreamEvent) {
        println("stream event")
    }
}

Answer 2

我无法让其他人在这个线程中提供的例子起作用。当然，他们编译了，但是一旦连接打开，他们就崩溃了。

但是，我在2014年的讨论(和iOS 8发布说明)中注意到，有一种新的方法来初始化NSStream，用于创建绑定的输入/输出流对。

见下文：

var inputStream: NSInputStream?
var outputStream: NSOutputStream?

NSStream.getStreamsToHostWithName("localhost", port: 1234, inputStream: &inputStream, outputStream: &outputStream)

这消除了对尴尬的CFStreamCreatePairWithSocketToHost调用的需求，也消除了对非托管资源的需求。

Answer 3

我想出了怎么做。几个重要的注意事项：

1. 如果使用&运算符，CMutablePointers将自动创建。
2. 您可以在带有T和getRetainedValue()的Unmanaged<T>中获得.getUnretainedValue() (似乎.getUnretainedValue()类似于__bridge_transfer)
3. 选项自动初始化为nil。
4. 如果可选的是nil，它将转换为false条件。

到目前为止，我(未经测试)：

var readStream: Unmanaged<CFReadStream>?
var writeStream: Unmanaged<CFWriteStream>?

CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, host, port, \
&readStream, &writeStream)

if (readStream && writeStream) {
    inputStream = readStream!.takeUnretainedValue();
    outputStream = writeStream!.takeUnretainedValue();
}