Please correct me if I am wrong or barking up the wrong tree.
There are different Mutex classes, one in mscorlib.Extensions and one in mscorlib. Both come under the System.Threading namespace. According this MSDN page. I can use the Mutex class in mscorlib.(Although, the phone symbol does not appear in the column before Name) I basically want to access the OpenExisting method from a Windows Phone 7.1 application. The default System.Threading.Mutex being used is in mscorlib.Extensions which does not have the OpenExisting method.
So, the question is, how do I make sure that the Mutex class that I access is from the mscorlib dll?
Should I un-reference mscorlib.extensions, what are the repercussions of doing so?
EDIT 1: Just figured that my application refers mscorlib[2.0.5.0] which does not have the Mutex class. I was looking at mscorlib[4.0.0.0] which has the Mutex class. In any case, is there a way for me to access the OpenExisting method?
EDIT 2: This question answers my question about referencing mscorlib [4.0.0.0]. So, I cannot use the OpenExisting method at all? Is the link to the Mutex class here, a reference to a wrong class?
As you can see on The MSDN Page for Mutex (Silverlight) the OpenExising method is not available for Silverlight.
So in short: You can't use it.
Related
I have a service IService that several components depend on. The components come and go depending on user actions.
It so happens that the implementation of IService is expensive, and I want 1 instance shared across all components. So far so good, I can use:
builder.RegisterType<ExpensiveStuff>().As<IService>().SingleInstance();
However, I don't want to ExpensiveStuff to live forever once built; I only want it to exist when one or more components holds a reference to it.
Is there a built in means of achieving this in Autofac?
I think you'll have to make sure that your usage of those dependencies happen within an instance scope.
The Orchard project could be a source of inspiration here. They use a set of scopes for Unit of Work; see the ShellContainerFactory.cs source file.
I am playing around with Entity Framework to see how it can be used in a new project I am working on. I put my edmx file in a class library so the Entities (and database access) can be used in multiple places. Currently I have a web project and a console project both referencing the class library.
One of my Entities has a Partial class defined with a static method. The purpose of the method is to accept some parameters and create one or more instances of the specific class. My first version of the method created an ObjectContext instance, created the Entity class (or classes), and returned the Entities to the calling method. The calling method then updated some properties and tried to save the Entities using a new ObjectContext instance. Obviously this did not work because the Entities were bound (correct term ??) to the Context created within the static method.
After some research, I modified the static method to also accept an ObjectContext reference to ensure that all the Entities where created and then later on manipulated and saved using the same Context. This works fine but the design just feels wrong.
Assuming that my one static method may grow into many more, or that my app (especially the web app) would probably benefit from additional layers (DAL or even a Service Layer), does it make sense for all these classes to require an ObjectContext parameter?
I have read on many postings that creating an ObjectContext via a Singleton pattern is a bad idea because "many clients would use the same object". My problem with that is I do not see how that is possible. In a local console app there is only a single user running the app. In a web app there would only be a single user on each request. Where is the user sharing problem? Not a single article/posting mentioned it...but where they referring to a Singleton pattern storing the object instance in the Application context?
I have also seen postings focused on web usage and storing the object instance in the users Session object via the HttpContext object. This makes sense but does not seem to address non-web usage.
I think that whatever solution is appropriate (static methodm, Factory object, etc.) would most likely be implemented in my class library so obviously it needs to support both web and non-web solutions. Maybe check for HttpContext to determine what environment it is running in.
I was hoping http://www.west-wind.com/weblog/posts/2008/Feb/05/Linq-to-SQL-DataContext-Lifetime-Management would be informative but I am having a hard time wrapping my head around the post and the example code seems like overkill for instantiating and sharing a simple object. (Although I am sure I am just not getting it...)
Any thoughts are appreciated.
Thanks.
The issue is not that “many clients would use the same object.” The issue is that the ObjectContext is intended to be a single unit of work. If you use it for many different units of work, you will find that there are a number of problems.
Memory usage will grow and grow.
Your application will become slower as object fixup has to do increasing amounts of work.
Multithreading won't work
The solution is to use the ObjectContext in the manner it is intended, namely, as a single unit of work.
I have been playing with the Facebook iOS API the past days and I got some questions. If I have two distinct view controllers that both need to use the Facebook object how should I share the object? And is it necessary to share it at all? I have been thinking of making a singleton. What I thought of doing was making a class "SocialMedia" that has a class method named "sharedFacebook".
Then I have another class named PREFIXFacebook where I conform to the session protocol and make an object. This class has an attribute named facebook. Then I instantiate this class in the SocialMedia class and send the method "facebook" to it and assign the returned object to the static Facebook variable in SocialMedia. Is that bad design? I have not been doing much singletons before, and I don't even know if it is necessary, but I don't want to duplicate the code.
Another approach would be to do this in the app delegate, but I read a post here on stack overflow and heard in one of the stanford iOS videos that it is bad to do such things with the global. Any thoughts?
As with most things, global variables are not bad in moderation. If you abuse them, you will be running short on Memory, but I think it is justified in this case. A singleton is essentially a global variable and I believe your plan here is a good one. Not only will it help you with Facebook, but it will help with other single-login sites such as Twitter and Google+.
To keep things with a small footprint, you don't want to store a million things in the Singleton class. Try to only store the bare minimum needed to avoid re-authenticating. This probably means only the Facebook object itself, and not an additional wrapper class for it.
I recently read about Dynamic Creation as one of the design pattern in Cocoa. However, I don't really understand how it works. So I need clarification from you who have implemented in your design.
What is it? Why and when would you use this design pattern?
I have read that you use NSClassFromString() to access the class. I assume that I use this when I want to use class that doesn't exist within the project I'm working on. Usually when I want to use certain class, I imported them in header. Does using this approach skip the #import process?
Class JavaArrayList = NSClassFromString(#"java.util.ArrayList");
I quote the code above as example. If do according to the code above, that means I can create a new JavaArrayList class and use the methods in it right?
JavaArrayList *foo = [[JavaArrayList alloc] init];
[foo useMethodBelongJava:doWhateverTask];
What are the benefits of using this design pattern? Especially in iPhone Development.
Your example appears to be using that pattern to instantiate a Java class. In the old days (up to about MacOS 10.4 I think), Apple had some technology called the Cocoa-Java Bridge, which let you use Java classes within Objective-C code. You had to instantiate them in the manner specified, because they didn't have Objective-C header files to import.
However, as of Snow Leopard, the Java Bridge no longer exists, so the code in your question won't work any more.
The recommended solution for calling a Java class from Objective-C is now JNI. Take a look at this question if that is what you're trying to do.
What is it? Why and when would you use this design pattern?
Coming back to NSClassFromString, it has other uses besides instantiating Java classes (which, as I mentioned, it doesn't do any more!). For an example, recently I wrote a library for parsing the response from a web service. In order to make it work with different web services, I had it read in a configuration file that described the data format it was expecting. For each field in the web service, my configuration file specified which Cocoa class to instantiate. Thus, in my code, I had a Cocoa class name as a string. To instantiate the object I wanted, I used NSClassFromString to turn it into a Class object.
Usually when I want to use certain class, I imported them in header. Does using this approach skip the #import process?
It can do. NSClassFromString will instantiate any class that is present at run time, so you don't need the header to be able to use it. If you don't have the header, you'll get a bunch of warnings of "may not respond to selector" whenever you try and use your newly instantiated class, as the compiler doesn't have enough information to be helpful. However, in many circumstances where NSClassFromString is useful, the header files aren't available.
See this link:
need advise about NSClassFromString
The only real benefit for iPhone was being able to reference classes from newer APIs and still target the old APIs. Since 4.0 you can do this anyway by setting the deployment target of your project. I can't really see any reason you would use it for iPhone programming any more.
This would only work for objective-C classes. You can't import java objects into your iphone app.
I'm currently developping my first iPhone application and I would like to know what is the best way to share an object which is gonna be used in every controller.
I was thinking of referencing the controller containing the needed data in other controllers and access this data thanks to properties, is that a good idea or is there a better way to do it?
Or can we declare any global variable (not const) accessible anywhere in the application?
Thank you
It's not clear from your question what kind of data you are dealing with, but one approach I have used in iphone applications is a singleton object that contains application state and state management functions.
There is a good discussion of the use of singletons versus app delegates for this type of data found at Cocoa With Love and I agree with what he has to say here.
For instance the application in this case had a user account tied to a web application so on load the application would initialize the singleton object and when the user signed in it would keep a reference to the user object in the singleton so that user info could be referenced for api calls.
This approach has worked fairly well for my purposes you can see how to create a singleton class in Objective-C here, and also in the apple docs here there are several ways to do it which provide the same functional result.
Once you have defined your singleton class you can initialize it in applicationDidFinishLaunching or in the viewDidLoad of your main controller and init the globally accessible data you are needing to manage. I highly recommend you read the Cocoa With Love article I linked above for some consideration of managing this whole process.
Hope that helps.
If you're stuck I can post some example code, but the singleton class examples available are pretty straightforward to work with.
If you really need it to be global, you can put it in the AppDelegate or create a data management object. But I think it's frowned upon to do it like that.