问题
The solution of this question no longer works with Swift 3.
There is no longer a property bytes
of Data
(formerly NSData
.
let data = dataToWrite.first!
self.outputStream.write(&data, maxLength: data.count)
With this code, I get the error:
Cannot convert value of type 'Data' to expected argument type 'UInt8'
How can you write Data
to an NSOutputStream
in Swift 3?
回答1:
NSData
had a bytes
property to access the bytes.
The new Data
value type in Swift 3 has a withUnsafeBytes()
method instead, which calls a closure with a pointer to the bytes.
So this is how you write Data
to an NSOutputStream
(without casting to NSData
):
let data = ... // a Data value
let bytesWritten = data.withUnsafeBytes { outputStream.write($0, maxLength: data.count) }
Remarks:
withUnsafeBytes()
is a generic method:
/// Access the bytes in the data.
///
/// - warning: The byte pointer argument should not be stored and used outside of the lifetime of the call to the closure.
public func withUnsafeBytes<ResultType, ContentType>(_ body: @noescape (UnsafePointer<ContentType>) throws -> ResultType) rethrows -> ResultType
In the above call,
both ContentType
and ResultType
are automatically inferred by
the compiler (as UInt8
and Int
), making additional
UnsafePointer()
conversions unnecessary.
outputStream.write()
returns the number of bytes actually written.
Generally, you should check that value. It can be -1
if
the write operation failed, or less than data.count
when writing
to sockets, pipes, or other objects with a flow control.
回答2:
Martin R, thank you for your answer. That was a foundation for a complete solution. Here it is:
extension OutputStream {
/// Write String to outputStream
///
/// - parameter string: The string to write.
/// - parameter encoding: The String.Encoding to use when writing the string. This will default to UTF8.
/// - parameter allowLossyConversion: Whether to permit lossy conversion when writing the string.
///
/// - returns: Return total number of bytes written upon success. Return -1 upon failure.
func write(_ string: String, encoding: String.Encoding = String.Encoding.utf8, allowLossyConversion: Bool = true) -> Int {
if let data = string.data(using: encoding, allowLossyConversion: allowLossyConversion) {
var bytesRemaining = data.count
var totalBytesWritten = 0
while bytesRemaining > 0 {
let bytesWritten = data.withUnsafeBytes {
self.write(
$0.advanced(by: totalBytesWritten),
maxLength: bytesRemaining
)
}
if bytesWritten < 0 {
// "Can not OutputStream.write(): \(self.streamError?.localizedDescription)"
return -1
} else if bytesWritten == 0 {
// "OutputStream.write() returned 0"
return totalBytesWritten
}
bytesRemaining -= bytesWritten
totalBytesWritten += bytesWritten
}
return totalBytesWritten
}
return -1
}
}
回答3:
Just use this extension:
Swift 5
extension OutputStream {
func write(data: Data) -> Int {
return data.withUnsafeBytes {
write($0.bindMemory(to: UInt8.self).baseAddress!, maxLength: data.count)
}
}
}
And for InputStream
extension InputStream {
func read(data: inout Data) -> Int {
return data.withUnsafeMutableBytes {
read($0.bindMemory(to: UInt8.self).baseAddress!, maxLength: data.count)
}
}
}
Swift 4
extension OutputStream {
func write(data: Data) -> Int {
return data.withUnsafeBytes { write($0, maxLength: data.count) }
}
}
extension InputStream {
func read(data: inout Data) -> Int {
return data.withUnsafeMutableBytes { read($0, maxLength: data.count) }
}
}
回答4:
Data
and NSData
are two separate classes in Swift 3, and Data
does not have the bytes
property.
The solution is to define data
as being of type NSData
let data: NSData = dataToWrite.first!
self.outputStream.write(UnsafePointer<UInt8>(data.bytes), maxLength: data.length)
According to Migrating to Swift 2.3 or Swift 3 from Swift 2.2:
The migrator will convert most uses of NSData to the new value type Data. However, there are certain methods on NSData that operate on UnsafeMutablePointer, while the corresponding methods on Data use UnsafeMutablePointer. (For example, NSData.getBytes(:length:) is more accepting than Data.copyBytes(:length:).) As a reminder, the in-memory layout of Swift types is not guaranteed.
来源:https://stackoverflow.com/questions/38090320/writing-data-to-an-nsoutputstream-in-swift-3