使用Swift中的write函数将NSData字节写入NSOutputStream时出错(“(()"与"UInt8""不同) [英] Error ("'()' is not identical to 'UInt8'") writing NSData bytes to NSOutputStream using the write function in Swift

问题描述

我正在尝试基于关于使用NSOutputStream代替NSData的答案是有意义的. /p>

但是，我无法正常工作.当我尝试将NSData字节(在我的NSURLConnection didReceiveData函数中)添加到NSOutputStream写入函数:'()' is not identical to 'UInt8'的这一行:bytesWritten = self.downloadStream.write(data.bytes, maxLength: bytesLeftToWrite)上时，出现此错误.

data.bytes的类型为ConstUnsafePointer<()>，并且.write()函数期望该类型为ConstUnsafePointer<UInt8>，因此从这种意义上说，错误是完全合理的.但是，由于我是iOS的新手，当然也不是Swift编程的新手，所以我无法集中精力解决此问题.

因此，如何将data.bytes: ConstUnsafePointer<()>转换为ConstUnsafePointer<UInt8> alt.通过其他方式进行这项工作?

我的didReceiveData功能:

func connection(connection: NSURLConnection!, didReceiveData data: NSData!) {

    var bytesLeftToWrite: NSInteger = data.length
    var bytesWritten: NSInteger = 0

    while bytesLeftToWrite > 0 {

        bytesWritten = self.downloadStream.write(data.bytes, maxLength: bytesLeftToWrite)

        if bytesWritten == -1 {

            break

        }

        bytesLeftToWrite -= bytesWritten

        let responseExpectedlenght: NSNumber = NSNumber(longLong: self.downloadResponse!.expectedContentLength)
        let dataLength: NSNumber = NSNumber(long: data.length)

        self.downloadProgressPercentage = ((dataLength / responseExpectedlenght) * 100)

        println("Downloaded: \(self.downloadProgressPercentage)%")

    }

}

解决方案

您可以使用UnsafePointer()投射指针:

bytesWritten = self.downloadStream.write(UnsafePointer(data.bytes), maxLength: bytesLeftToWrite)

在写循环中也有一个问题，因为您总是写 数据对象的 initial 字节到输出流.

它可能看起来像这样(未经测试):

var bytes = UnsafePointer<UInt8>(data.bytes)
var bytesLeftToWrite: NSInteger = data.length

while bytesLeftToWrite > 0 {
    let bytesWritten = self.downloadStream.write(bytes, maxLength: bytesLeftToWrite)
    if bytesWritten == -1 {
        break // Some error occurred ...
    }

    bytesLeftToWrite -= bytesWritten
    bytes += bytesWritten // advance pointer

    // ...
}

I'm trying to build an asynchronous file download in Swift based on the Erica Sadun's method. But I need it to handle bigger files, so I found this answer about using a NSOutputStream instead of NSData, makes sense.

However, I can't get it to work. I get this error when I try adding the NSData bytes (in my NSURLConnection didReceiveData function) to the NSOutputStream write function: '()' is not identical to 'UInt8' on this row: bytesWritten = self.downloadStream.write(data.bytes, maxLength: bytesLeftToWrite).

data.bytes is of the type ConstUnsafePointer<()> and the .write() function expects the type to be ConstUnsafePointer<UInt8>, so in that sense, the error make perfect sense. But since I'm new to iOS and of course Swift programming, I can't get my head around how to fix this.

So, how do I convert the data.bytes: ConstUnsafePointer<()> to ConstUnsafePointer<UInt8> alt. make this work some other way?

My didReceiveData function:

func connection(connection: NSURLConnection!, didReceiveData data: NSData!) {

    var bytesLeftToWrite: NSInteger = data.length
    var bytesWritten: NSInteger = 0

    while bytesLeftToWrite > 0 {

        bytesWritten = self.downloadStream.write(data.bytes, maxLength: bytesLeftToWrite)

        if bytesWritten == -1 {

            break

        }

        bytesLeftToWrite -= bytesWritten

        let responseExpectedlenght: NSNumber = NSNumber(longLong: self.downloadResponse!.expectedContentLength)
        let dataLength: NSNumber = NSNumber(long: data.length)

        self.downloadProgressPercentage = ((dataLength / responseExpectedlenght) * 100)

        println("Downloaded: \(self.downloadProgressPercentage)%")

    }

}

解决方案

You can cast the pointer with UnsafePointer():

bytesWritten = self.downloadStream.write(UnsafePointer(data.bytes), maxLength: bytesLeftToWrite)

There is also a problem in your write loop, because you always write the initial bytes of the data object to the output stream.

It should probably look similar to this (untested):

var bytes = UnsafePointer<UInt8>(data.bytes)
var bytesLeftToWrite: NSInteger = data.length

while bytesLeftToWrite > 0 {
    let bytesWritten = self.downloadStream.write(bytes, maxLength: bytesLeftToWrite)
    if bytesWritten == -1 {
        break // Some error occurred ...
    }

    bytesLeftToWrite -= bytesWritten
    bytes += bytesWritten // advance pointer

    // ...
}

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