What does "DisplayClass" name mean when calling lambda? - c#

According to this answer when code uses local variables from inside lambda methods the compiler will generate extra classes that can have name such as c__DisplayClass1. For example the following (completely useless) code:
class Program
{
static void Main()
{
try {
implMain();
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
static void implMain()
{
for (int i = 0; i < 10; i++) {
invoke(() => {
Console.WriteLine(i);
throw new InvalidOperationException();
});
}
}
static void invoke(Action what)
{
what();
}
}
outputs the following call stack:
System.InvalidOperationException
at ConsoleApplication1.Program.<>c__DisplayClass2.<implMain>b__0()
at ConsoleApplication1.Program.invoke(Action what)
at ConsoleApplication1.Program.implMain()
at ConsoleApplication1.Program.Main()
Note that there's c__DisplayClass2 in there which is a name of a class generated by the compiler to hold the loop variable.
According to this answer c__DisplayClass "means"
c --> anonymous method closure class ("DisplayClass")
Okay, but what does "DisplayClass" mean here?
What does this generated class "display"? In other words why is it not "MagicClass" or "GeneratedClass" or any other name?

From an answer to a related question by Eric Lippert:
The reason that a closure class is called "DisplayClass" is a bit unfortunate: this is jargon used by the debugger team to describe a class that has special behaviours when displayed in the debugger. Obviously we do not want to display "x" as a field of an impossibly-named class when you are debugging your code; rather, you want it to look like any other local variable. There is special gear in the debugger to handle doing so for this kind of display class. It probably should have been called "ClosureClass" instead, to make it easier to read disassembly.

You can get some insight from the C# compiler source as available from the SSCLI20 distribution, csharp/sccomp subdirectory. Searching the code for "display" gives most hits in the fncbind.cpp source code file. You'll see it used in code symbols as well as comments.
The comments strongly suggest that this was a term used internally by the team, possibly as far back as the design meetings. This is .NET 2.0 vintage code, there was not a lot of code rewriting going on yet. Just iterators and anonymous methods, both implemented in very similar ways. The term "display class" is offset from "user class" in the comments, a clear hint that they used the term to denote auto-generated classes. No strong hint why "display" was favored, I suspect that it might have something to do with these classes being visible in the metadata of the assembly.

Based on Reflector, DisplayClass can be translated as CompilerGeneratedClass
[CompilerGenerated]
private sealed class <>c__DisplayClass16b
{
// Fields
public MainForm <>4__this;
public object sender;
// Methods
public void <cmdADSInit_Click>b__16a()
{
ADS.Initialize();
this.<>4__this._Sender = this.sender;
this.<>4__this.SelectedObject = ADS.Instance;
}
}

Related

Custom keyword coloring in Visual Studio 2010+

I'm trying to add custom coloring for only certain keywords in my Visual Studio editor for C# code. I want to be able to color any type that implements IDisposable as a different color. Ideally I'd like to create a simple list of classes/interfaces that derive from IDisposable in some sort of configuration that I can edit. (Although if you said there was a method/plugin that would automatically find all disposable types and color them independently that would be the Holy Grail).
I've done a ton of research and it looks like an "editor classifier" extension might do the trick. However I created one that merely tries to color the word "Stream" and although it does hit my code that attempts to highlight that word, it does not end up highlighted in the editor.
I have added my VS extension to Github here
This really seems like this should be fairly straightforward but I have gone down many alleys on this one only to find dead-ends. Is there a simpler way to do this, or is my extension broken?
Update
Very strange. I just ran my extension again and although it does not highlight the text in the editor it highlights all instances of "Stream" in the popup text when you hover over a type/variable! Is there any way to get it to apply to the editor?
Depending on wether you are using Jetbrains Resharper or not you may write a plugin for that. That way you are able not only to add visual notification of IDisposable on a variable but also provide quickfixes if, and only if, it is not beeing called, which is what i am assuming you want to catch. Mind you that i can imagine that there's already a R# plugin for that. I know i've considered this too, but i was too lazy to write a plugin for that.
Don't get me wrong btw - If you're not using r# yet you should consider trying it out.
Among others you'd be working with this: API-QuickFix
There are also ways to define custom keywords, as resharper does, given by a custom markup and apply quickfixes to that.
PS: No i don't work at jetbrains. it's just that good :)
UPDATE:
potential VS Extension fix?
check this one out: MSDN Link Highlighting Text
I tried opening your github project but couldn't so i thought i'll just check msdn instead. it seems you are deriving from the wrong class to fulfill your needs?
MSDN keyword "Editors - Extending the Editor - Walkthrough: Highlighting Text"
I know SO wants code on the site, but msdn links going down is rather unlikely and with the given information the content can be found easily enough :)
I'm a bit late to the party, but hey, why not throw my 2 cents in.
As you've explained in your question, your project has two basic parts:
Finding the classes that implement IDisposable
Highlighting them
The first is by far the hardest, though not impossible. A word-list based approach is probably the simplest, though it should be possible with Roslyn to figure out on the fly which classes inherit IDisposible.
You could also always resort to loading the project's compiled .exe/.dll in the background after a build and figuring out what the types are there, but you'd still have to write some magic glue code to figure out what short class names in the code referred to what actual full-name classes in the assembly.
The second part, highlighting, is quite easy once you know how to do it (it helps that I've spent the last several months working full-time on extending VS). Of course, with Visual Studio, nothing is as simple as it looks (despite the efforts of Microsoft to try to make it user-friendly). So, I've built a sample extension that highlights just classes named "Stream" within C# files to get you started.
The relevant code is below, and the full project source is on GitHub). It starts with a classification-tagger provider:
[Export(typeof(ITaggerProvider))]
[ContentType("CSharp")]
[TagType(typeof(ClassificationTag))]
[Name("HighlightDisposableTagger")]
public class HighlightDisposableTaggerProvider : ITaggerProvider
{
[Import]
private IClassificationTypeRegistryService _classificationRegistry = null;
[Import]
private IClassifierAggregatorService _classifierAggregator = null;
private bool _reentrant;
public ITagger<T> CreateTagger<T>(ITextBuffer buffer) where T : ITag
{
if (_reentrant)
return null;
try {
_reentrant = true;
var classifier = _classifierAggregator.GetClassifier(buffer);
return new HighlightDisposableTagger(buffer, _classificationRegistry, classifier) as ITagger<T>;
}
finally {
_reentrant = false;
}
}
}
Then the tagger itself:
public class HighlightDisposableTagger : ITagger<ClassificationTag>
{
private const string DisposableFormatName = "HighlightDisposableFormat";
[Export]
[Name(DisposableFormatName)]
public static ClassificationTypeDefinition DisposableFormatType = null;
[Export(typeof(EditorFormatDefinition))]
[Name(DisposableFormatName)]
[ClassificationType(ClassificationTypeNames = DisposableFormatName)]
[UserVisible(true)]
public class DisposableFormatDefinition : ClassificationFormatDefinition
{
public DisposableFormatDefinition()
{
DisplayName = "Disposable Format";
ForegroundColor = Color.FromRgb(0xFF, 0x00, 0x00);
}
}
public event EventHandler<SnapshotSpanEventArgs> TagsChanged = delegate { };
private ITextBuffer _subjectBuffer;
private ClassificationTag _tag;
private IClassifier _classifier;
private bool _reentrant;
public HighlightDisposableTagger(ITextBuffer subjectBuffer, IClassificationTypeRegistryService typeService, IClassifier classifier)
{
_subjectBuffer = subjectBuffer;
var classificationType = typeService.GetClassificationType(DisposableFormatName);
_tag = new ClassificationTag(classificationType);
_classifier = classifier;
}
public IEnumerable<ITagSpan<ClassificationTag>> GetTags(NormalizedSnapshotSpanCollection spans)
{
if (_reentrant) {
return Enumerable.Empty<ITagSpan<ClassificationTag>>();
}
var tags = new List<ITagSpan<ClassificationTag>>();
try {
_reentrant = true;
foreach (var span in spans) {
if (span.IsEmpty)
continue;
foreach (var token in _classifier.GetClassificationSpans(span)) {
if (token.ClassificationType.IsOfType(/*PredefinedClassificationTypeNames.Identifier*/ "User Types")) {
// TODO: Somehow figure out if this refers to a class which implements IDisposable
if (token.Span.GetText() == "Stream") {
tags.Add(new TagSpan<ClassificationTag>(token.Span, _tag));
}
}
}
}
return tags;
}
finally {
_reentrant = false;
}
}
}
I've only tested this on VS2010, but it should work for VS2013 too (the only thing that might be different is the class classification name, but that's easy to discover with a well-placed breakpoint). I've never written an extension for VS2012, so I can't comment on that, but I know it's quite close to VS2013 in most respects.
So, one possible solution(I believe this one works):
1) Create your own content type which inherits from csharp.
2) Create new TextViewCreationListener which will swap out all "csharp" content types with your own one, thus potentially "disarming" all the other classifiers.
3) Register your classifier to handle your own content type.
Here is some of the code:
[Export(typeof(IVsTextViewCreationListener))]
[ContentType("csharp")]
[TextViewRole(PredefinedTextViewRoles.Editable)]
class TextViewCreationListener : IVsTextViewCreationListener {
internal readonly IVsEditorAdaptersFactoryService _adaptersFactory;
[Import] internal IContentTypeRegistryService ContentTypeRegistryService = null;
[ImportingConstructor]
public TextViewCreationListener(IVsEditorAdaptersFactoryService adaptersFactory) {
_adaptersFactory = adaptersFactory;
}
#region IVsTextViewCreationListener Members
public void VsTextViewCreated(VisualStudio.TextManager.Interop.IVsTextView textViewAdapter) {
var textView = _adaptersFactory.GetWpfTextView(textViewAdapter);
var myContent = ContentTypeRegistryService.GetContentType(MyContentType);
if(myContent == null)
{
ContentTypeRegistryService.AddContentType(MyContentType, new[] {"csharp"});
myContent = ContentTypeRegistryService.GetContentType(MyContentType);
}
// some kind of check if the content type is not already MyContentType.
textView.TextBuffer.ChangeContentType(myContent, null);
}
#endregion
}
And now, just modify your IClassifierProvider to register with your own content type, as such: [ContentType(MyContentType)]
Iin your own IClassifier, you can basically do your own calculation and once you think you can't handle the stuff, you could pass the control to other classifiers.
If you use MEF and import IClassifierAggregatorService, you can get a "MASTER-classifier" which will run all the logic for you. I haven't implemented it yet, but I've suggestes something similiar in the past, and it seemed to work. Alternatively you could maybe use [ImportMany] with List<IClassifier> and filter out the csharp ones?!

Why are "DisplayClass" and calling method name ordered this way in the stack trace?

First of all, I've read this answer and no, it only says how it is implemented right now, but doesn't explain why.
Here's a sample program (same as here):
class Program
{
static void Main()
{
try {
implMain();
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
static void implMain()
{
for (int i = 0; i < 10; i++) {
invoke(() => {
Console.WriteLine(i);
throw new InvalidOperationException();
});
}
}
static void invoke(Action what)
{
what();
}
}
which outputs the following call stack:
System.InvalidOperationException
at ConsoleApplication1.Program.<>c__DisplayClass2.<implMain>b__0()
at ConsoleApplication1.Program.invoke(Action what)
at ConsoleApplication1.Program.implMain()
at ConsoleApplication1.Program.Main()
Note these two lines:
at ConsoleApplication1.Program.<>c__DisplayClass2.<implMain>b__0()
at ConsoleApplication1.Program.invoke(Action what)
The lower one (with invoke()) says that there's namespace ConsoleApplication1 with class Program in it that has member invoke(). Here left-to-right corresponds to outer-to-inner.
The upper one (with c__DisplayClass2) says again there's a namespace and a class...
and then there's c__DisplayClass2 which means "a magic name the compiler chosen for storing captured variables" and then there's <implMain> as if it is a parameter to c__DisplayClass2. So it reads as if c__DisplayClass2 somehow is part of Program and implMain is part of c__DisplayClass2.
Now as I see it it's logically the opposite - there's implMain() method and there's "magic class" c__DisplayClass2 crafted specifically for implMain() local variables. So to me it looks like the upper line should look like this:
at ConsoleApplication1.Program.implMain.c__DisplayClass2.b__0()
(maybe with some extra symbols to prevent possible conflicts) but I hope my idea is clear - this way it would look like c__DisplayClass2 is crafted specifically to facilitate implMain() functioning.
Is there any reason why the current implementation shows the method name (implMain) after the local variables capture class name (c__DisplayClass2) and not vice versa?
<implMain>b__0() is just the name of the method.
Inspection in a disassembler will show you this. The < and > does not imply generics.
The inclusion of implMain probably just hints where the delegate was created.

What is the Behavior of a Dynamic Attribute in a Static (Extension) Class in C# (MVC3)

I am new to developing in .NET and C#, but have been a long-time developer, working with C, C++, Java, PHP, etc.
I have an MVC3 extension class for my data models that refers to the database. It is set as "private static" in the class, but I think that it is not keeping up with database changes. In other words, when I change data in the controllers, those changes aren't "noticed" in the db because it is static. Currently, I am creating and disposing of the variable for each use, to compensate.
My questions are:
Am I correct that a static db variable could behave that way?
Is it necessary to dispose of the dynamic variable in the static class, or will garbage collection still take care of it automatically?
Here is a relevant snippet of the class:
namespace PBA.Models {
using System;
using System.Text.RegularExpressions;
using PBA.Models;
using PBA.Controllers;
public static class Extensions {
private static PbaDbEntities db = null;
public static PbaDbEntities GetDb() {
// TODO: find out about static memory/disposal, etc.
//
if (db != null) {
db.Dispose();
}
db = new PbaDbEntities();
return db;
}
public static string GetCheckpointState(this Activity activity, long memberProjectId) {
GetDb(); // TODO: Do I need to do this each time, or will a one-time setting work?
string state = CheckpointController.CHECKPOINT_STATUS_NOT_STARTED;
try {
var sub = db.ActivitySubmissions.
Where(s => s.activityId == activity.activityId).
Where(s => s.memberProjectId == memberProjectId).
OrderByDescending(s => s.submitted).
First();
if (sub != null) {
state = sub.checkpointStatusId;
}
}
catch (Exception e) {
// omitted for brevity
}
return state;
}
}
}
Your code will fail horribly in production.
DataContexts are not thread-safe; you must not share a context between requests.
Never put mutable objects in static fields in multi-threaded applications.
Ignoring exceptions that way is a terrible idea, if you don't want to handle exceptions just don't try/catch, or catch & rethrow. Think about it like this, after you've buried the exception, your program is in an invalid state, b/c something you have no control over error'd out. Now, b/c you've buried the exception, your program can continue to operate but it's in a bad state.
If your code makes it to production, 3.5 yrs from now some jr. programmer is going to get involved in some middle of the night firestorm because all of a sudden the website is broken, even though it used to work. It will be completely impossible to track down where the exception is happening so, this poor guy is going to spend 48 straight hours adding logging code all over the place to track down the problem. He will find that some DBA somewhere decided to rename the column MemberProjectId to MemberProjectIdentifier, which caused your linq to blow up.
Think of the children, handle exceptions, don't bury them.
btw - yes, i have been that guy that has to figure out these types of mistakes.
It seems like you need to read about mvc3 and entity framework before writing coding and asking in here for help on something that's coded full of bad practices.
Answering your questions:
1- no
2- makes no sense as the answer to 1
Do it right, here are some useful documentation: http://msdn.microsoft.com/en-us/library/ie/gg416514(v=vs.98).aspx
EDIT: Adding some explicit fix
You could access your dbcontext from an static class, something like this:
var context = DbProvider.CurrentDb;
The idea is to access your db from here always: from your extension methods and from your controller actions.
Then, the implementation of the DbProvider.CurrentDb will be something like this:
public static classDbProvider {
public static void Initialize(){
HttpContext.Current.ApplicationInstance.BeginRequest += CreateDb;
HttpConetxt.Current.ApplicationInstance.EndRequest += DisposeDb;
}
private static void CreateDb(object sender, EventArgs e) {
HttpContext.Items.Add("CurrentDb", new PbaDbEntities(););
}
private static void DisposeDb(object sender, EventArgs e)
{
Current.Dispose();
HttpContext.Items.Remove("CurrentDb");
}
public static PbaDbEntities CurrentDb{
get {
return (PbaDbEntities)HttpContext.Current.Items["CurrentDb"];
}
}
}
As you can see, it will create a new Db per each request and it will be available ONLY in that request. In that way, your db will be disposed at the end of each request. This pattern is called Open-Session-in-View.
Finally, you need to initialize the DbProvider calling the method
Initialize() in your Global.asax file, in the event Application_start.
Hope it helps.
I don't have any idea of the context here-- if db is simply a connection-like object or not, but it appears you are throwing away and recreating whatever it is unnecessarily.
Best to create a property (for whatever your doing) so to be consistent.
private static Thing _thing;
private static Thing thing{
get{
if(_thing==null){
_thing=new Thing();
}
return _thing;
}
}

StyleCop Custom Rules: Method Parameters and Variables

I am new to StyleCop, and I need to implement own coding standarts for the place I work. I am using VS2005 and cannot debug it. Upgrading to VS2008/2010 is not an option for us now.
I wonder many things:
1) How can I identify the methods parameters? I tried the below but do not know where to go, SDK documentation is not really helpful.
private bool VisitElement(CsElement element, CsElement parentElement, object context)
{
if (element.ElementType == ElementType.Method)
{
...
2) How can I find out that a declaration do not follow an assignment? Ex.given.
int i; // Wrong, give warning
int i = 0; // True usage
3) How can I find out that a document does not contain only 1 namespace or only 1 class inside it and how can I get their identifiers (names)?
True:
namespace Hello
{
class P{
}
}
-
Wrong:
namespace Hi {
class C {
}
class E {
}
}
namespace Ho {
class D {
}
}
4) How can I find out function calls and find out where to? (i.e. Blocking a call to specific function)
For #1, take a look at the Microsoft.StyleCop.CSharp.ReadabilityRules.CheckMethodParameters method implementation (either in Reflector or at http://stylecop.codeplex.com/SourceControl/changeset/view/64d44becb157#Project%2fSrc%2fAddIns%2fCSharp%2fAnalyzers%2fReadabilityRules.MethodParameters.cs).
For #2, something like the following should do the trick:
private bool VisitExpression(Expression expression, Expression parentExpression, Statement parentStatement, CsElement parentElement, object context)
{
if (expression.ExpressionType == ExpressionType.VariableDeclarator)
{
VariableDeclaratorExpression declaratorExpression = (VariableDeclaratorExpression)expression;
if (declaratorExpression.Initializer == null)
{
this.AddViolation(parentElement, expression.LineNumber, "YourRule", declaratorExpression.Identifier.Text);
}
}
return true;
}
The existing SA1402 (FileMayOnlyContainASingleClass) and SA1403 (FileMayOnlyContainASingleNamespace) rules should take care of #3. If they don't work for your scenario, please specify what you would like a custom rule to do differently.
#4 should be an FxCop rule, not a StyleCop rule since it has nothing to do with source code style.

Most Useful Attributes [closed]

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I know that attributes are extremely useful. There are some predefined ones such as [Browsable(false)] which allows you to hide properties in the properties tab. Here is a good question explaining attributes: What are attributes in .NET?
What are the predefined attributes (and their namespace) you actually use in your projects?
[DebuggerDisplay] can be really helpful to quickly see customized output of a Type when you mouse over the instance of the Type during debugging. example:
[DebuggerDisplay("FirstName={FirstName}, LastName={LastName}")]
class Customer
{
public string FirstName;
public string LastName;
}
This is how it should look in the debugger:
Also, it is worth mentioning that [WebMethod] attribute with CacheDuration property set can avoid unnecessary execution of the web service method.
System.Obsolete is one of the most useful attributes in the framework, in my opinion. The ability to raise a warning about code that should no longer be used is very useful. I love having a way to tell developers that something should no longer be used, as well as having a way to explain why and point to the better/new way of doing something.
The Conditional attribute is pretty handy too for debug usage. It allows you to add methods in your code for debug purposes that won't get compiled when you build your solution for release.
Then there are a lot of attributes specific to Web Controls that I find useful, but those are more specific and don't have any uses outside of the development of server controls from what I've found.
[Flags] is pretty handy. Syntactic sugar to be sure, but still rather nice.
[Flags]
enum SandwichStuff
{
Cheese = 1,
Pickles = 2,
Chips = 4,
Ham = 8,
Eggs = 16,
PeanutButter = 32,
Jam = 64
};
public Sandwich MakeSandwich(SandwichStuff stuff)
{
Console.WriteLine(stuff.ToString());
// ...
}
// ...
MakeSandwich(SandwichStuff.Cheese
| SandwichStuff.Ham
| SandwichStuff.PeanutButter);
// produces console output: "Cheese, Ham, PeanutButter"
Leppie points out something I hadn't realized, and which rather dampens my enthusiasm for this attribute: it does not instruct the compiler to allow bit combinations as valid values for enumeration variables, the compiler allows this for enumerations regardless. My C++ background showing through... sigh
I like [DebuggerStepThrough] from System.Diagnostics.
It's very handy for avoiding stepping into those one-line do-nothing methods or properties (if you're forced to work in an early .Net without automatic properties). Put the attribute on a short method or the getter or setter of a property, and you'll fly right by even when hitting "step into" in the debugger.
For what it's worth, here's a list of all .NET attributes. There are several hundred.
I don't know about anyone else but I have some serious RTFM to do!
My vote would be for Conditional
[Conditional("DEBUG")]
public void DebugOnlyFunction()
{
// your code here
}
You can use this to add a function with advanced debugging features; like Debug.Write, it is only called in debug builds, and so allows you to encapsulate complex debug logic outside the main flow of your program.
I always use the DisplayName, Description and DefaultValue attributes over public properties of my user controls, custom controls or any class I'll edit through a property grid. These tags are used by the .NET PropertyGrid to format the name, the description panel, and bolds values that are not set to the default values.
[DisplayName("Error color")]
[Description("The color used on nodes containing errors.")]
[DefaultValue(Color.Red)]
public Color ErrorColor
{
...
}
I just wish Visual Studio's IntelliSense would take the Description attribute into account if no XML comment are found. It would avoid having to repeat the same sentence twice.
[Serializable] is used all the time for serializing and deserializing objects to and from external data sources such as xml or from a remote server. More about it here.
In Hofstadtian spirit, the [Attribute] attribute is very useful, since it's how you create your own attributes. I've used attributes instead of interfaces to implement plugin systems, add descriptions to Enums, simulate multiple dispatch and other tricks.
Here is the post about interesting attribute InternalsVisibleTo. Basically what it does it mimics C++ friends access functionality. It comes very handy for unit testing.
I've found [DefaultValue] to be quite useful.
I'd suggest [TestFixture] and [Test] - from the nUnit library.
Unit tests in your code provide safety in refactoring and codified documentation.
[XmlIgnore]
as this allows you to ignore (in any xml serialisation) 'parent' objects that would otherwise cause exceptions when saving.
It's not well-named, not well-supported in the framework, and shouldn't require a parameter, but this attribute is a useful marker for immutable classes:
[ImmutableObject(true)]
I like using the [ThreadStatic] attribute in combination with thread and stack based programming. For example, if I want a value that I want to share with the rest of a call sequence, but I want to do it out of band (i.e. outside of the call parameters), I might employ something like this.
class MyContextInformation : IDisposable {
[ThreadStatic] private static MyContextInformation current;
public static MyContextInformation Current {
get { return current; }
}
private MyContextInformation previous;
public MyContextInformation(Object myData) {
this.myData = myData;
previous = current;
current = this;
}
public void Dispose() {
current = previous;
}
}
Later in my code, I can use this to provide contextual information out of band to people downstream from my code. Example:
using(new MyContextInformation(someInfoInContext)) {
...
}
The ThreadStatic attribute allows me to scope the call only to the thread in question avoiding the messy problem of data access across threads.
The DebuggerHiddenAttribute which allows to avoiding step into code which should not be debugged.
public static class CustomDebug
{
[DebuggerHidden]
public static void Assert(Boolean condition, Func<Exception> exceptionCreator) { ... }
}
...
// The following assert fails, and because of the attribute the exception is shown at this line
// Isn't affecting the stack trace
CustomDebug.Assert(false, () => new Exception());
Also it prevents from showing methods in stack trace, useful when having a method which just wraps another method:
[DebuggerHidden]
public Element GetElementAt(Vector2 position)
{
return GetElementAt(position.X, position.Y);
}
public Element GetElementAt(Single x, Single y) { ... }
If you now call GetElementAt(new Vector2(10, 10)) and a error occurs at the wrapped method, the call stack is not showing the method which is calling the method which throws the error.
DesignerSerializationVisibilityAttribute is very useful. When you put a runtime property on a control or component, and you don't want the designer to serialize it, you use it like this:
[DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
public Foo Bar {
get { return baz; }
set { baz = value; }
}
Only a few attributes get compiler support, but one very interesting use of attributes is in AOP: PostSharp uses your bespoke attributes to inject IL into methods, allowing all manner of abilities... log/trace being trivial examples - but some other good examples are things like automatic INotifyPropertyChanged implementation (here).
Some that occur and impact the compiler or runtime directly:
[Conditional("FOO")] - calls to this method (including argument evaluation) only occur if the "FOO" symbol is defined during build
[MethodImpl(...)] - used to indicate a few thing like synchronization, inlining
[PrincipalPermission(...)] - used to inject security checks into the code automatically
[TypeForwardedTo(...)] - used to move types between assemblies without rebuilding the callers
For things that are checked manually via reflection - I'm a big fan of the System.ComponentModel attributes; things like [TypeDescriptionProvider(...)], [TypeConverter(...)], and [Editor(...)] which can completely change the behavior of types in data-binding scenarios (i.e. dynamic properties etc).
If I were to do a code coverage crawl, I think these two would be top:
[Serializable]
[WebMethod]
I have been using the [DataObjectMethod] lately. It describes the method so you can use your class with the ObjectDataSource ( or other controls).
[DataObjectMethod(DataObjectMethodType.Select)]
[DataObjectMethod(DataObjectMethodType.Delete)]
[DataObjectMethod(DataObjectMethodType.Update)]
[DataObjectMethod(DataObjectMethodType.Insert)]
More info
In our current project, we use
[ComVisible(false)]
It controls accessibility of an individual managed type or member, or of all types within an assembly, to COM.
More Info
[TypeConverter(typeof(ExpandableObjectConverter))]
Tells the designer to expand the properties which are classes (of your control)
[Obfuscation]
Instructs obfuscation tools to take the specified actions for an assembly, type, or member. (Although typically you use an Assembly level [assembly:ObfuscateAssemblyAttribute(true)]
The attributes I use the most are the ones related to XML Serialization.
XmlRoot
XmlElement
XmlAttribute
etc...
Extremely useful when doing any quick and dirty XML parsing or serializing.
Being a middle tier developer I like
System.ComponentModel.EditorBrowsableAttribute Allows me to hide properties so that the UI developer is not overwhelmed with properties that they don't need to see.
System.ComponentModel.BindableAttribute Some things don't need to be databound. Again, lessens the work the UI developers need to do.
I also like the DefaultValue that Lawrence Johnston mentioned.
System.ComponentModel.BrowsableAttribute and the Flags are used regularly.
I use
System.STAThreadAttribute
System.ThreadStaticAttribute
when needed.
By the way. I these are just as valuable for all the .Net framework developers.
[EditorBrowsable(EditorBrowsableState.Never)] allows you to hide properties and methods from IntelliSense if the project is not in your solution. Very helpful for hiding invalid flows for fluent interfaces. How often do you want to GetHashCode() or Equals()?
For MVC [ActionName("Name")] allows you to have a Get action and Post action with the same method signature, or to use dashes in the action name, which otherwise would not be possible without creating a route for it.
I consider that is important to mention here that the following attributes are also very important:
STAThreadAttribute
Indicates that the COM threading model for an application is single-threaded apartment (STA).
For example this attribute is used in Windows Forms Applications:
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
}
And also ...
SuppressMessageAttribute
Suppresses reporting of a specific static analysis tool rule violation, allowing multiple suppressions on a single code artifact.
For example:
[SuppressMessage("Microsoft.Performance", "CA1801:ReviewUnusedParameters", MessageId = "isChecked")]
[SuppressMessage("Microsoft.Performance", "CA1804:RemoveUnusedLocals", MessageId = "fileIdentifier")]
static void FileNode(string name, bool isChecked)
{
string fileIdentifier = name;
string fileName = name;
string version = String.Empty;
}
Off the top of my head, here is a quick list, roughly sorted by frequency of use, of predefined attributes I actually use in a big project (~500k LoCs):
Flags, Serializable, WebMethod, COMVisible, TypeConverter, Conditional, ThreadStatic, Obsolete, InternalsVisibleTo, DebuggerStepThrough.
I generates data entity class via CodeSmith and I use attributes for some validation routine. Here is an example:
/// <summary>
/// Firm ID
/// </summary>
[ChineseDescription("送样单位编号")]
[ValidRequired()]
public string FirmGUID
{
get { return _firmGUID; }
set { _firmGUID = value; }
}
And I got an utility class to do the validation based on the attributes attached to the data entity class. Here is the code:
namespace Reform.Water.Business.Common
{
/// <summary>
/// Validation Utility
/// </summary>
public static class ValidationUtility
{
/// <summary>
/// Data entity validation
/// </summary>
/// <param name="data">Data entity object</param>
/// <returns>return true if the object is valid, otherwise return false</returns>
public static bool Validate(object data)
{
bool result = true;
PropertyInfo[] properties = data.GetType().GetProperties();
foreach (PropertyInfo p in properties)
{
//Length validatioin
Attribute attribute = Attribute.GetCustomAttribute(p,typeof(ValidLengthAttribute), false);
if (attribute != null)
{
ValidLengthAttribute validLengthAttribute = attribute as ValidLengthAttribute;
if (validLengthAttribute != null)
{
int maxLength = validLengthAttribute.MaxLength;
int minLength = validLengthAttribute.MinLength;
string stringValue = p.GetValue(data, null).ToString();
if (stringValue.Length < minLength || stringValue.Length > maxLength)
{
return false;
}
}
}
//Range validation
attribute = Attribute.GetCustomAttribute(p,typeof(ValidRangeAttribute), false);
if (attribute != null)
{
ValidRangeAttribute validRangeAttribute = attribute as ValidRangeAttribute;
if (validRangeAttribute != null)
{
decimal maxValue = decimal.MaxValue;
decimal minValue = decimal.MinValue;
decimal.TryParse(validRangeAttribute.MaxValueString, out maxValue);
decimal.TryParse(validRangeAttribute.MinValueString, out minValue);
decimal decimalValue = 0;
decimal.TryParse(p.GetValue(data, null).ToString(), out decimalValue);
if (decimalValue < minValue || decimalValue > maxValue)
{
return false;
}
}
}
//Regex validation
attribute = Attribute.GetCustomAttribute(p,typeof(ValidRegExAttribute), false);
if (attribute != null)
{
ValidRegExAttribute validRegExAttribute = attribute as ValidRegExAttribute;
if (validRegExAttribute != null)
{
string objectStringValue = p.GetValue(data, null).ToString();
string regExString = validRegExAttribute.RegExString;
Regex regEx = new Regex(regExString);
if (regEx.Match(objectStringValue) == null)
{
return false;
}
}
}
//Required field validation
attribute = Attribute.GetCustomAttribute(p,typeof(ValidRequiredAttribute), false);
if (attribute != null)
{
ValidRequiredAttribute validRequiredAttribute = attribute as ValidRequiredAttribute;
if (validRequiredAttribute != null)
{
object requiredPropertyValue = p.GetValue(data, null);
if (requiredPropertyValue == null || string.IsNullOrEmpty(requiredPropertyValue.ToString()))
{
return false;
}
}
}
}
return result;
}
}
}
[DeploymentItem("myFile1.txt")]
MSDN Doc on DeploymentItem
This is really useful if you are testing against a file or using the file as input to your test.
[System.Security.Permissions.PermissionSetAttribute] allows security actions for a PermissionSet to be applied to code using declarative security.
// usage:
public class FullConditionUITypeEditor : UITypeEditor
{
// The immediate caller is required to have been granted the FullTrust permission.
[PermissionSetAttribute(SecurityAction.LinkDemand, Name = "FullTrust")]
public FullConditionUITypeEditor() { }
}

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