在C#中，內存流（MemoryStream）默認是不可擴展的，即在寫入大量數據時可能會導致內存不足的問題。解決這個問題的一種方法是使用可擴展內存流（ExpandableMemoryStream），它是一個自定義的內存流類，可以根據需要動態擴展內存大小。

下面是一個簡單的可擴展內存流的示例代碼：

public class ExpandableMemoryStream : Stream
{
private byte[] buffer;
private int position;
private int length;
public ExpandableMemoryStream()
{
buffer = new byte[4096]; // 初始大小為4KB
position = 0;
length = 0;
}
public override bool CanRead => true;
public override bool CanSeek => true;
public override bool CanWrite => true;
public override long Length => length;
public override long Position
{
get => position;
set => position = (int)value;
}
public override void Flush()
{
// 無需實現
}
public override int Read(byte[] buffer, int offset, int count)
{
int bytesRead = Math.Min(count, length - position);
Array.Copy(this.buffer, position, buffer, offset, bytesRead);
position += bytesRead;
return bytesRead;
}
public override long Seek(long offset, SeekOrigin origin)
{
switch (origin)
{
case SeekOrigin.Begin:
position = (int)offset;
break;
case SeekOrigin.Current:
position += (int)offset;
break;
case SeekOrigin.End:
position = length - (int)offset;
break;
}
return position;
}
public override void SetLength(long value)
{
if (value <= length)
{
length = (int)value;
if (position > length)
position = length;
}
else
{
int newSize = (int)value;
byte[] newBuffer = new byte[newSize];
Array.Copy(buffer, newBuffer, length);
buffer = newBuffer;
length = newSize;
}
}
public override void Write(byte[] buffer, int offset, int count)
{
int newPosition = position + count;
if (newPosition > this.buffer.Length)
{
int newSize = Math.Max(newPosition, this.buffer.Length * 2);
byte[] newBuffer = new byte[newSize];
Array.Copy(this.buffer, newBuffer, position);
this.buffer = newBuffer;
}
Array.Copy(buffer, offset, this.buffer, position, count);
position = newPosition;
length = Math.Max(position, length);
}
}

使用可擴展內存流時，可以像使用內存流一樣進行讀寫操作，但不用擔心內存不足的問題。當寫入的數據量超過當前內存大小時，可擴展內存流會自動擴展內存大小，以適應更多的數據。

ExpandableMemoryStream stream = new ExpandableMemoryStream();
byte[] data = new byte[8192]; // 假設有8KB數據需要寫入
stream.Write(data, 0, data.Length);
// 讀取數據
byte[] buffer = new byte[4096];
int bytesRead = stream.Read(buffer, 0, buffer.Length);

這樣，就能夠解決C#內存流不可擴展的問題。