Quick Answer

Prevent use of disposed objects.

Understanding the Issue

Thrown when using disposed resources like streams or database connections. Ensure proper disposal patterns.

The Problem

This code demonstrates the issue:

Csharp Error 
var stream = new MemoryStream();
stream.Dispose();
stream.ReadByte(); // Throws

The Solution

Here's the corrected code:

Csharp Fixed 
// Solution 1: using statement
using (var stream = new MemoryStream())
{
    stream.ReadByte();
} // Auto-disposed

// Solution 2: Null check after disposal
private Stream _stream;
public void Process()
{
    if (_stream == null)
        throw new ObjectDisposedException(nameof(_stream));
    // Use stream
}

Key Takeaways

Always follow IDisposable patterns.