Documentation for Ice 3.5. The latest release is Ice 3.7. Refer to the space directory for other releases.

Inserting a User Exception in C#

As in the case of Ice objects, a Dynamic Ice application may represent user exceptions in a native format that is not directly compatible with the Ice API. If the application needs to raise such a user exception to the Ice run time, the exception must be wrapped in a subclass of Ice.UserException. The Dynamic Ice API provides a class to simplify this process:

C#
namespace Ice
{
    public abstract class UserExceptionWriter : UserException
    {
        public UserExceptionWriter(Communicator communicator);

        public abstract void write(OutputStream os);

        // ...
    }
}

A subclass of UserExceptionWriter is responsible for supplying a communicator to the constructor, and for implementing the following methods:

Extracting a User Exception in C#

An application extracts a user exception by calling one of two versions of the throwException method defined in the InputStream class:

C#
namespace Ice {
    public interface InputStream {
        void throwException();
        void throwException(UserExceptionReaderFactory factory);

        // ...
    }
}

The version without any arguments attempts to locate and throw a C# implementation of the encoded exception using classes generated by the Slice-to-C# compiler.

If your goal is to create an exception in another type system, such as a native PHP exception object, you must call the second version of throwException and pass an implementation of UserExceptionReaderFactory:

C#
namespace Ice {
    public interface UserExceptionReaderFactory {   
        void createAndThrow(string typeId);
    }
}

As the stream iterates over slices of an exception from most-derived to least-derived, it invokes createAndThrow passing the type ID of each slice, giving the application an opportunity to raise an instance of UserExceptionReader:

C#
namespace Ice {
    public abstract class UserExceptionReader : UserException {
        protected UserExceptionReader(Communicator communicator);

        public abstract void read(InputStream is);

        public abstract string ice_name();

        protected Communicator _communicator;
    }
}

Subclasses of UserExceptionReader must implement the abstract functions. In particular, the implementation of read must call InputStream.startException, unmarshal the remaining slices, and then call InputStream.endException.

See Also

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