在C#中，内存流（MemoryStream）默认是不可扩展的，即在写入大量数据时可能会导致内存不足的问题。解决这个问题的一种方法是使用可扩展内存流（ExpandableMemoryStream），它是一个自定义的内存流类，可以根据需要动态扩展内存大小。
下面是一个简单的可扩展内存流的示例代码：
```csharp
public class ExpandableMemoryStream : Stream
{
private byte[] buffer;
private int position;
private int length;
public ExpandableMemoryStream()
{
buffer = new byte[4096]; // 初始大小为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()
{
// 无需实现
}
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);
}
}
```
使用可扩展内存流时，可以像使用内存流一样进行读写操作，但不用担心内存不足的问题。当写入的数据量超过当前内存大小时，可扩展内存流会自动扩展内存大小，以适应更多的数据。
```csharp
ExpandableMemoryStream stream = new ExpandableMemoryStream();
byte[] data = new byte[8192]; // 假设有8KB数据需要写入
stream.Write(data, 0, data.Length);
// 读取数据
byte[] buffer = new byte[4096];
int bytesRead = stream.Read(buffer, 0, buffer.Length);
```
这样，就能够解决C#内存流不可扩展的问题。
