Example:
I have an user control with 1 property (that one editable through Property Grid) called "Title".
There is a way to throw an compile-time exception if the property "Title" is empty? Or all design-time properties is optional?
There is no way at compile time to ensure a particular property is set. You can use the #error directive to cause a compile time error or #warning for a compile time warning if code is compiled but this is not what you want.
There are two ways of ensuring a particular property or method is set. The first is to require it in a constructor or check that it has been set in a subsequent method or property. This is a runtime check, not compile time and, as you say, you have certain restrictions in a UserControl.
The second way is to use a code analysis tool like FXCop. You could write a custom rule that identifies all instances of your UserControl and ensures the property has been set on all instances. It may also be possible with Roslyn or PostSharp but I am not familiar enough with those tools to say so.
The problem with code analysis tools like FXCop is there is a rather steep learning curve. Programming languages are complex and these tools need to expose the complexity. My recommendation is use a default value like "insert title here" or, in the unlikely even that there is no suitable default, throw an exception when the control is rendered with a descriptive message.
See Good way to ensure that a property on a UserControl gets set? for a similar case.
Related
For context, using C# inside the Unity3D Editor.
I have more and more often started using enums to loosely couple things to settings.
For example i am setting up an item, and i want to give it a visual from a pool of defined visuals. That visual is basically a class that contains a sprite, a color, and a model attached to an integer unique ID. From this Unique ID, i generate an Enum. And it takes some effort to verify that the UniqueID is actually Unique, and catch some edge cases regarding that.
The benefit of doing the above, is that the enum is all that has to be stored on the item, to link it to the visual. At runtime there is a dictionary created to lookup the enum, and then request the stored visual to be loaded/used. This loosely couples the visuals to the item, so loading the item list does not automatically load all of the visual assets associated with the item. The last part is unity default behavior and is really annoying, and it really slows down the game and consumes a massive amount of RAM in this default behavior.
As a result we have a lot of those enums for various purposes and a lot of lookup stuff happening. And currently we are having no big problems with it.
However, the enums and the editing/generation of those enums is error prone in the sense that when values are removed, the items (and any other interested parties) are non the wiser, which then has to be either tested before build, or runs into a safety catch/error at runtime.
My question is. Is this a blatant abuse of Enums? And if so, what would be a better way of approaching this problem of loose coupling?
If it is not, what would be a better way to set up and manage these enums in a safe way? So alarm bells will go off if anything using the enum now has an invalid value, or the values meaning would change? Which i imagine is hardly possible, and requires code all over the place to "self check" on recompile?
Or does this just all boil down to team discipline to manage the values well, and know what the enums mean and represent? In which case, it would never be able to make this designer friendly unless i write a custom editor for each and every one of these.
Thanks for any insights you might be able to provide.
If I understand you correctly, you're trying to associate each item with one of multiple static visuals? If this is the case you can simply write each visual as a static readonly object inside the visuals class. In your "item" objects you can then make a field called e.g. "visual" and set this to reference the right visual.
I don't know what makes the visuals load, but if the constructor does, then I believe they will load when the visual class is first used at runtime.
How can I track a variable's values as they change, at runtime, in C#? I'm interested in the same functionality that the debugger provides when I'm tracing a variable through execution steps, only that I need to call upon it from my code. Some sort of key-value observing, but for all kinds of variables(local, class, static, etc), not only properties. So, basically, receive a notification when a variable's value changes.
You are working from the assumption that the debugger can track variable changes. It can't.
It is possible with unmanaged code, the processor has dedicated debug registers that allow setting data breakpoints. Up to three are provided. It generates a hardware interrupt when it sees a particular memory location getting written. This otherwise very useful feature isn't available in managed code however. The garbage collector is completely incompatible with it, it moves objects around, giving them another address.
The managed debugger does support a "when hit" condition on a breakpoint, allowing you to dump info to the output window. That however requires a breakpoint, it cannot be triggered by a change in variable value. It also really slows down code execution since the debugger actually enters a break state before executing the condition.
The obvious place to put such a breakpoint is in a property setter. Which is what you'll need to implement this feature in code. You can do anything you want in that setter, using the Trace class for example.
To add to what Marc said, if you want to do this for lots of properties and methods you might want to check out aspect oriented programming techniques, and libraries such as PostSharp.
http://www.sharpcrafters.com/postsharp
The managed debugger uses the ICorDebug COM API for pretty much everything. The part that you're interested is ICorDebugValue and its descendants. Note that a LOT of the debugging API requires that the process be not running (ie, have encountered a breakpoint) in order for the various inspections to happen. A high level overview of ICorDebug is here. The documentation on it is kinda sparse, but some Googling may help. Good luck.
The only sensible way you could do that without the debugger would be: don't use a variable, but use a property, and (perhaps conditionally) add trace to the setter:
private int myValue;
public int MyValue {
get {return myValue;}
set {
SomeTraceMethod(myValue, value, ...);
myValue = value;
}
}
Obviously this cannot then be used for arbitrary fields/variables.
As others mentioned a mechanism like that makes only sense when using properties. In .NET you can then make use of the INotifyPropertyChanged interface.
For a sample how to implement it see
How to: Implement the INotifyPropertyChanged Interface
The referenced article talks explicitly about Windows Forms, but you are not bound to that (the interface is actually declared in the System.ComponentModel namespace in System.dll). In fact, this interface is widely used for data binding scenarios, e.g. in WPF.
From within a class library, I'd like to know if it is being accessed during design mode as opposed to normal runtime.
I tried using System.ComponentModel.LicenseManager.UsageMode but it seemed to have a value of Runtime even when I was editing a form.
UPDATE:
To clarify, I want to know if I am in design mode not from within a component, but rather from within a separate class that happens to be called by other items from within a form or control. I have a Utility class which is being called indirectly from a control and it is there that I need to know if I am in design mode or not.
I don't think Component.DesignMode will help in this case. What if the component or control is not loaded on the forms designer ? What you may try in this case is, create an enum that only sets the one value at normal startup which otherwise remains to another value by default. You can now check the value of the enum instance and decide if it's a design-time or runtime.
You can use Component.DesignMode to check this. However, be aware that this will always report false inside the constructor of the component, so it needs to be checked later. For details, see Debugging Design-Time Controls.
Edit in response to comments and edit:
Unfortunately, the LicenseMananger, as well as most other services which provide information about whether you're in Design Time (including Component.DesignMode and DesignerProperties.IsInDesignMode) as specifically geared at handling user interface elements. This makes sense, as they're intended to tell you when your item is being "designed" on a designer surface, which requires the component to be registered in the designer.
There is no single property that will cleanly tell you this from within an arbitrary class.
I could see two options, both of which are less than ideal:
Pass the required information into your class (ie: a Component or DependencyObject), so the methods above can be used to check for design-time access correctly. This is probably a more maintainable approach, and will likely work properly in more situations.
Resort to the "hack" of checking the current process name and looking for "devenv" - this is pretty awful, as it assumes Visual Studio only, relies on the executable name, etc... In general, I'll mention it because you'll find it with enough searching, but wouldn't recommend it, as it's very easy to circumvent and has many limitations and flaws.
Is it not possible to use Component.DesignMode property?
Here's some info on applying attributes in order to get design-time specific behavior: http://msdn.microsoft.com/en-us/library/37899azc.aspx
I have some classes, which have several methods which I don't really want to be there, but are there simply because the XML Serializer needs them. Is there anyway to generate compile-time errors/warnings if they get called from user-code?
I am aware that I can implement IXmlSerializable, and I am also aware that I can separate out the classes into purely data storage classes, however, I am not asking a question about how I should design such a system, I am simply asking if there is a way to generate compile-time errors/warnings if they are called by anything that is not the XML serializer...
You can add
[Obsolete]
to the method. The IsError property of ObsoleteAttribute controls whether an error or warning is generated, and you can provide an explanatory message too.
You could decorate the members in question with the ObsoleteAttribute. Its intention is a bit different, but it will generate compiler warnings (or errors) when called from user code.
You can hide the methods from users intellisense using the [EditorBrowsable] attribute, and from property designer using [Browsable], attribute.
I don't recommend using the [ObsoleteAttribute], because it conveys a different meaning to what method state actually is. Instead use a comment indicating that the method should not be used from user code.
Also keep in mind that there are lot's of users that compile their code with threat warnings as errors, which will make impossible for them to compile valid code, in this case.
I've recently found the need to check at compile-time whether either: a) a certain assembly reference exists and can be successfully resolved, or b) a certain class (whose fully qualified name is known) is defined. These two situations are equivalent for my purposes, so being able to check for one of them would be good enough. Is there any way to do this in .NET/C#? Preprocessor directives initially struck me as something that might help, but it seems it doesn't have the necessary capability.
Of course, checking for the existence of a type at runtime can be done easily enough, but unfortunately that won't resolve my particular problem in this situation. (I need to be able to ignore the fact that a certain reference is missing and thus fall-back to another approach in code.)
Is there a reason you can't add a reference and then use a typeof expression on a type from the assembly to verify it's available?
var x = typeof(SomeTypeInSomeAssembly);
If the assembly containing SomeTypeInSomeAssembly is not referenced and available this will not compile.
It sounds like you want the compiler to ignore one branch of code, which is really only doable by hiding it behind an #if block. Would defining a compiler constant and using #if work for your purposes?
#if MyConstant
.... code here that uses the type ....
#else
.... workaround code ....
#endif
Another option would be to not depend on the other class at compile-time at all, and use reflection or the .NET 4.0 dynamic keyword to use it. If it'll be called repeatedly in a perf-critical scenario in .NET 3.5 or earlier, you could use DynamicMethod to build your code on first use instead of using reflection every time.
I seem to have found a solution here, albeit not precisely for what I was initially hoping.
My Solution:
What I ended up doing is creating a new build configuration and then defining a precompiler constant, which I used in code to determine whether to use the reference, or to fall back to the alternative (guaranteed to work) approach. It's not fully automatic, but it's relatively simple and seems quite elegant - good enough for my purposes.
Alternative:
If you wanted to fully automate this, it could be done using a pre-build command that runs a Batch script/small program to check the availabilty of a given reference on the machine and then updates a file containing precompiler constants. This however I considered more effort than it was worth, though it may have been more useful if I had multiple independent references that I need to resolve (check availability).