_context.ChangeTracker 'threw an exception of type 'System.ObjectDisposedException'

_context.ChangeTracker 'threw an exception of type 'System.ObjectDisposedException'

A System.ObjectDisposedException is a runtime error that occurs when an object has been disposed of and is no longer available for use. This error can occur in any type of application, including web applications, console applications, and mobile applications.

In the context of a .NET application, this exception typically occurs when an object that was created using the `using` statement or the `IDisposable` interface has been disposed of before it is properly released. This can happen if the object is no longer needed by the application, or if there is a bug in the code that causes the object to be disposed of prematurely.

When this exception occurs, it can cause the application to crash or behave unexpectedly. It is important for developers to understand what causes this error and how to prevent it from occurring in their applications.

One common cause of a System.ObjectDisposedException is using the `using` statement incorrectly. The `using` statement is used to create an object and automatically dispose of it when it is no longer needed. However, if the object is not properly released before it is disposed of, this can cause the exception to occur.

For example, consider the following code

csharp
using (var fileStream = new FileStream("example.txt", FileMode.Open))
{
    using (var reader = new StreamReader(fileStream))
    {
        // Read from the stream
    }
}

In this code, a `FileStream` object is created and used to open a file for reading. The `StreamReader` object is then created and used to read from the file. However, because both objects are created using the `using` statement, they will be automatically disposed of when the block of code is exited.

This means that if there is any code inside the block of code that causes an exception to occur, it will be caught by the `using` statement and the application will crash with a System.ObjectDisposedException. To prevent this from happening, it is important to make sure that all objects created using the `using` statement are properly released before they are disposed of.

Another common cause of a System.ObjectDisposedException is using the `IDisposable` interface incorrectly. The `IDisposable` interface is used to allow objects to be manually disposed of by the garbage collector. However, if an object that implements this interface is not properly released before it is disposed of, this can cause the exception to occur.

For example, consider the following code

csharp
class MyClass 
 IDisposable
{
    private Stream stream;
    public MyClass(Stream stream)
    {
        this.stream = stream;
    }
    public void Dispose()
    {
        // Release the stream
        stream.Close();
    }
}

In this code, a `MyClass` object is created and used to read from a file. The `IDisposable` interface is implemented by the class, allowing it to be manually disposed of by the garbage collector. However, if there is any code inside the block of code that causes an exception to occur, it will be caught by the `Dispose` method and the application will crash with a System.ObjectDisposedException.

To prevent this from happening, it is important to make sure that all objects that implement the `IDisposable` interface are properly released before they are disposed of. This can be done using the `using` statement or by manually calling the `Dispose` method on the object.

In addition to using the `using` statement and the `IDisposable` interface correctly, it is also important to make sure that all objects created using the `new` keyword are properly released before they are disposed of. This can be done by manually calling the `Dispose` method on the object or by using a `finally` block to ensure that the object is always released, even if an exception occurs.

For example, consider the following code

csharp
class MyClass
{
    private Stream stream;
    public MyClass(Stream stream)
    {
        this.stream = stream;
    }
    public void Dispose()
    {
        // Release the stream
        stream.Close();
    }
}