.NET中的IDisposable接口和using语句是什么？如何正确释放非托管资源？

public interface IDisposable
{
    void Dispose();
}

<pre class="brush:php;toolbar:false;">using (var fileStream = new FileStream("data.txt", FileMode.Open))
{
    // 使用文件流读写数据
    var buffer = new byte[1024];
    fileStream.Read(buffer, 0, buffer.Length);
} // 在这里自动调用 fileStream.Dispose()

<pre class="brush:php;toolbar:false;">FileStream fileStream = null;
try
{
    fileSteam = new FileStream("data.txt", FileMode.Open);
    var buffer = new byte[1024];
    fileStream.Read(buffer, 0, buffer.Length);
}
finally
{
    fileStream?.Dispose();
}

<pre class="brush:php;toolbar:false;">public class MyClass : IDisposable
{
    private IntPtr _handle; // 非托管资源
    private bool _disposed = false;
<pre class="brush:php;toolbar:false;"><code>public MyClass()
{
    _handle = AllocateSomeUnmanagedResource(); // 假设这是一个非托管句柄
}

public void Dispose()
{
    Dispose(true);
    GC.SuppressFinalize(this); // 已手动清理，无需终结器
}

protected virtual void Dispose(bool disposing)
{
    if (_disposed) return;

    if (disposing)
    {
        // 释放托管资源（如果有）
    }

    // 释放非托管资源
    if (_handle != IntPtr.Zero)
    {
        FreeUnmanagedResource(_handle);
        _handle = IntPtr.Zero;
    }

    _disposed = true;
}

~MyClass()
{
    Dispose(false); // 终结器兜底
}

[DllImport("someunmanaged.dll")]
private static extern IntPtr AllocateSomeUnmanagedResource();

[DllImport("someunmanaged.dll")]
private static extern void FreeUnmanagedResource(IntPtr handle);

<pre class="brush:php;toolbar:false;">using var conn = new SqlConnection(connString);
using var cmd = new SqlCommand(sql, conn);
conn.Open();
cmd.ExecuteNonQuery();
// 自动按逆序释放