使用默认构造函数时，未初始化的串行端口属性是否被赋予了默认值？

Question

如果使用默认构造函数或无参数构造函数创建串行端口，则端口将被赋予默认值。 From the documentation:

// Create a new SerialPort object with default settings.
_serialPort = new SerialPort();

当未指定任何属性值时，此构造函数使用默认属性值。例如，DataBits 属性默认为 8，Parity 属性默认为 None 枚举值，StopBits 属性默认为 1，默认端口名称为 COM1。

有several constructors

使用带参数的构造函数时：
在使用带参数的构造函数和使用默认构造函数时，不在串口的构造函数参数内的属性是否被赋予相同的默认值？

this question中的问题，有趣的答案，cmets和随后的聊天讨论让我问这个。

Answer 1

您可以查看它的source code 并查看构造函数和归档定义。

您将看到所有重要的属性，包括 PortName、BaudRate、DataBits、Parity 和 StopBits，都有一个默认值，如果它们不存在于构造函数参数中，则默认值将用于他们。

还有一些其他重要的属性，它们也有默认值，虽然它们不存在于构造函数中，但是在某些情况下，它们的默认值可能不是很好。

例如对于HandShake，默认值为Handshake.None;，而您可能希望将其设置为Handshake.XOnXOff、Handshake.RequestToSend 或Handshake.RequestToSendXOnXOff。对于这个特定的属性，您可能需要参考 Hans 的comments。

看看构造函数：

public SerialPort(System.ComponentModel.IContainer container)
{
    container.Add(this);
}
public SerialPort()
{
}
// Non-design SerialPort constructors here chain, 
//using default values for members left unspecified by parameters
public SerialPort(string portName) 
    : this (portName, defaultBaudRate, defaultParity, defaultDataBits, defaultStopBits)
{
}
public SerialPort(string portName, int baudRate) 
    : this (portName, baudRate, defaultParity, defaultDataBits, defaultStopBits)
{
}
public SerialPort(string portName, int baudRate, Parity parity)
    : this (portName, baudRate, parity, defaultDataBits, defaultStopBits)
{
}
public SerialPort(string portName, int baudRate, Parity parity, int dataBits)
    : this (portName, baudRate, parity, dataBits, defaultStopBits)
{
}
public SerialPort(string portName, int baudRate, Parity parity, 
     int dataBits, StopBits stopBits)
{
    this.PortName = portName;
    this.BaudRate = baudRate;
    this.Parity = parity;
    this.DataBits = dataBits;
    this.StopBits = stopBits;
}

以下是这些字段和默认值定义：

// ---------- default values -------------*

private const int defaultDataBits = 8;
private const Parity defaultParity = Parity.None;
private const StopBits defaultStopBits = StopBits.One;
private const Handshake defaultHandshake = Handshake.None;
private const int defaultBufferSize = 1024;
private const string defaultPortName = "COM1";
private const int defaultBaudRate = 9600;
private const bool defaultDtrEnable = false;
private const bool defaultRtsEnable = false;
private const bool defaultDiscardNull = false;
private const byte defaultParityReplace = (byte) '?';
private const int defaultReceivedBytesThreshold = 1;
private const int defaultReadTimeout = SerialPort.InfiniteTimeout;
private const int defaultWriteTimeout = SerialPort.InfiniteTimeout;
private const int defaultReadBufferSize = 4096;
private const int defaultWriteBufferSize = 2048;
private const int maxDataBits = 8;
private const int minDataBits = 5;
private const string defaultNewLine = "\n";

private const string SERIAL_NAME = @"\Device\Serial";

// --------- members supporting exposed properties ------------*
private int baudRate = defaultBaudRate;
private int dataBits = defaultDataBits;
private Parity parity = defaultParity;
private StopBits stopBits = defaultStopBits;
private string portName = defaultPortName;
// ASCII is default encoding for modem communication, etc.
private Encoding encoding = System.Text.Encoding.ASCII; 
private Decoder decoder = System.Text.Encoding.ASCII.GetDecoder();
private int maxByteCountForSingleChar = System.Text.Encoding.ASCII.GetMaxByteCount(1);
private Handshake handshake = defaultHandshake;
private int readTimeout = defaultReadTimeout;
private int writeTimeout = defaultWriteTimeout;
private int receivedBytesThreshold = defaultReceivedBytesThreshold;
private bool discardNull = defaultDiscardNull;
private bool dtrEnable = defaultDtrEnable;
private bool rtsEnable = defaultRtsEnable;
private byte parityReplace = defaultParityReplace;
private string newLine = defaultNewLine;
private int readBufferSize = defaultReadBufferSize;
private int writeBufferSize = defaultWriteBufferSize;