The CORRECT Way to Code a Custom Exception Class

BY: Doug Seelinger

There is a lot of advice out there on how to go about building your own custom exception classes.  A lot of these sources are at least partially correct. Some are totally wrong.  Some even advocate abandoning the base System.Exception class altogether, but that’s throwing the baby out with the bathwater, in my opinion.  None that I’ve seen show how to serialize/deserialize your custom exception class should it have additional data in it’s subclass. It’s enough to make one despair of ever finding the “right” way to build an exception class. 

A lot of the confusion around exceptions comes about if you’ve ever actually tried to serialize an exception using an Xml-based serializer.  You are testing the code you write, correct? When attempting to serialize your nice new exception class with something like XmlSerializer, the serializer will simply choke, stating that it can’t serialize any class that has an IDictionary member.  And System.Exception has an IDictionary in it.  Yet every piece of literature coming out of Microsoft says that we should build custom exceptions (sub-typed from Exception, and not ApplicationException) and mark them as [Serializable].  What gives?  Well, there are more serializers in the world than just the XML-based serializers, and that’s when it’s important to serialize exceptions.  The System.Runtime.Serialization.Formatters.Binary.BinaryFormatter, for example, serializes exceptions just fine.

So, how do you derive from Exception correctly, particularly if you’ve got additional information in your custom exception class?  I thought you’d never ask.

    [Serializable]
    public class AuthorizationRequiredException : Exception
    {
        public string ResourceReferenceProperty { get; set; }
 
        public AuthorizationRequiredException()
        {
        }
 
        public AuthorizationRequiredException(string message)
            : base(message)
        {
        }
 
        public AuthorizationRequiredException(string message, Exception inner)
            : base(message, inner)
        {
        }
 
        protected AuthorizationRequiredException(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
            ResourceReferenceProperty = info.GetString("ResourceReferenceProperty");
        }
 
        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public override void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            if (info == null)
                throw new ArgumentNullException("info");
            info.AddValue("ResourceReferenceProperty", ResourceReferenceProperty);
            base.GetObjectData(info, context);
        }
 
    }

  And here are the tests that drive it to completion (updated to show better testing methods):

    [TestClass]
    public class AuthorizationRequiredExceptionTests
    {
        [TestMethod]
        public void AuthorizationRequiredException_default_ctor()
        {
            // Arrange
            const string expectedMessage = "Exception of type 'MyApp.Exceptions.AuthorizationRequiredException' was thrown.";
 
            // Act
            var sut = new AuthorizationRequiredException();
 
            // Assert
            Assert.IsNull(sut.ResourceReferenceProperty);
            Assert.IsNull(sut.InnerException);
            Assert.AreEqual(expectedMessage, sut.Message);
        }
 
        [TestMethod]
        public void AuthorizationRequiredException_ctor_string()
        {
            // Arrange
            const string expectedMessage = "message";
 
            // Act
            var sut = new AuthorizationRequiredException(expectedMessage);
 
            // Assert
            Assert.IsNull(sut.ResourceReferenceProperty);
            Assert.IsNull(sut.InnerException);
            Assert.AreEqual(expectedMessage, sut.Message);
        }
 
        [TestMethod]
        public void AuthorizationRequiredException_ctor_string_ex()
        {
            // Arrange
            const string expectedMessage = "message";
            var innerEx = new Exception("foo");
 
            // Act
            var sut = new AuthorizationRequiredException(expectedMessage, innerEx);
 
            // Assert
            Assert.IsNull(sut.ResourceReferenceProperty);
            Assert.AreEqual(innerEx, sut.InnerException);
            Assert.AreEqual(expectedMessage, sut.Message);
        }
 
        [TestMethod]
        public void AuthorizationRequiredException_serialization_deserialization_test()
        {
            // Arrange
            var innerEx = new Exception("foo");
            var originalException = new AuthorizationRequiredException("message", innerEx) { ResourceReferenceProperty = "MyReferenceProperty" };
            var buffer = new byte[4096];
            var ms = new MemoryStream(buffer);
            var ms2 = new MemoryStream(buffer);
            var formatter = new BinaryFormatter();
 
            // Act
            formatter.Serialize(ms, originalException);
            var deserializedException = (AuthorizationRequiredException)formatter.Deserialize(ms2);
 
            // Assert
            Assert.AreEqual(originalException.ResourceReferenceProperty, deserializedException.ResourceReferenceProperty);
            Assert.AreEqual(originalException.InnerException.Message, deserializedException.InnerException.Message);
            Assert.AreEqual(originalException.Message, deserializedException.Message);
        }
 
        [TestMethod]
        [ExpectedException(typeof(ArgumentNullException))]
        public void AuthorizationRequiredException_GetObjectData_throws_exception_when_info_null()
        {
            // Arrange
            var sut = new AuthorizationRequiredException("message") { ResourceReferenceProperty = "MyReferenceProperty" };
 
            // Act
            // ReSharper disable AssignNullToNotNullAttribute
            sut.GetObjectData(null, new StreamingContext());
            // ReSharper restore AssignNullToNotNullAttribute
 
            // Assert
            // [ExpectedException(typeof(ArgumentNullException))]
        }
    }

If you use this code as a template for creating your custom exceptions, you won’t go too far wrong, I think.

As far as XML-based serializers goes, I hope that the Base Class Library team will take some time and just fix the “chokes on IDictionary” issue.  Frankly, it’s quite embarrassing.

 

Reference Site : See Here

 

Keep Coding:)

Thanks 🙂

iDev: Enable or Disable ARC

iDev: Enable or Disable ARC

Enable ARC on OLD files : 

I want to bring a single Objective-C class written using ARC into an old project.

Add -fobjc-arc flag to any files for which you’d like to enable ARC, as described in the ARC documentation

If you want to enable ARC for many files, you have to:

1. Open “Build phases” –> “Compile sources”
2. Select files with “left_mouse” + “cmd” (for separated files) or “shift” (for grouped files – select first and last)
3. Press “enter”
4. Paste -fobjc-arc
5. Press “Enter/Done”.

Disable ARC on MULTIPLE files:

Add -fno-objc-arc flag to any files for which you’d like to disable ARC, as described in the ARC documentation

If you want to disable ARC for many files, you have to:

1. Open “Build phases” –> “Compile sources”
2. Select files with “left_mouse” + “cmd” (for separated files) or “shift” (for grouped files – select first and last)
3. Press “enter”
4. Paste -fno-objc-arc
5. Press “Enter/Done”.

Keep Coding 🙂

Thanks…….

iDev: Test Flight: Beta Deployments for iOS Apps

Hello Friends : 

A new post for you…….

One of the more challenging things in creating iOS applications is the whole provisioning and deployment process.  This becomes especially true during beta testing of your application using Ad-Hoc distribution.

The process is something like this:

1. Gather all the UDIDs from your test subjects
2. Enter these into the iOS Provisioning Portal
3. Create a distribution certificate (if you haven’t already)
4. Create an Ad-Hoc provisioning profile
5. Download the profile and certificate
6. Configure and build your app signing with these credentials

Then, your testers need to get the application and install it.  Generally like this:

1. Email the testers the provisioning profile and app bundle
2. The tester need to drag both to iTunes (or Organizer) and then tether and sync

This makes it a little cumbersome for most testers and difficult for non-tech savvy users.  One could post the app bundle to a website with a manifest and then create a launch page (like an internal app store) and then notify the users.  This is where Test Flight (www.testflightapp.com) comes in … managing the web-delivery of your application in a really easy-to-use process.

Remembering the above, now I do this:

1. (optional) Ask your test users to register their devices
2. (optional) Create a team out of these testers and download their device IDs
3. (optional) Upload all of these device IDs at one time to the Provisioning Portal
4. Follow the same process as above to create a provisioning profile and build
5. Now upload the IPA bundle to Test Flight and I am done

At this point, the testers can receive a notification of the new build (and subsequent builds) and simply visit Test Flight on their device.  They will be able to install your beta app straight from the browser.  Further, I can report on who has installed the app and who has not.

All this and the website has a nice easy to use design on top of that!

Thanks ;

Keep Coding 🙂