Maybe I'm not understanding the situation correctly, but we're told it's important to have only one instance of the RxBleClient.
Couldn't this be easily accomplished by making it a static member of the Application class?
class MyApp extends Application {
static RxBleClient rxBleClient;
...
}
Also, I'm having a hard time understanding this code (from your Application class):
public static RxBleClient getRxBleClient(Context context) {
RxBleApp application = (RxBleApp) context.getApplicationContext();
return application.rxBleClient;
}
Could you help me understand what it's doing, and why? Why couldn't it simply
return rxBleClient;
It can be accomplished with taking the static member of the class. Tough it is more elegant to pass it through the instance of RxBleApp which make it more testable (if there were any tests for the sample part).
The RxBleClient is referenced in the RxBleApp which is the android Application. The application context can be retrieved from the Context.
Related
I'm trying to get an understanding of which concrete types are providing the implementations of interfaces in an IOC (dependency injection) container. My implementation works fine when there are no delegates involved. However, I'm having trouble when a delegate method is passed as the type factory, as I can't get Mono.Cecil to give me the concrete type or a method reference to the factory back. I'm specifically in this case trying to build a component that can work with the IServiceCollection container for .Net ASP.Net REST APIs. I've created a 'minimised' set of code below to make it easy to explain the problem.
Consider the following C# code:
interface IServiceProvider {}
interface IServiceCollection {}
class ServicesCollection : IServiceCollection {}
interface IMongoDBContext {}
class MongoDBContext : IMongoDBContext
{
public MongoDBContext(string configName) {}
}
static class Extensions
{
public static IServiceCollection AddSingleton<TService>(this IServiceCollection services, Func<IServiceProvider, TService> implementationFactory) where TService : class
{
return null;
}
}
class Foo
{
void Bar()
{
IServiceCollection services = new ServicesCollection();
services.AddSingleton<IMongoDBContext>(s => new MongoDBContext("mongodbConfig"));
}
}
When successfully locating the 'services.AddSingleton' as a MethodReference, I'm unable to see any reference to the MongoDBContext class, or its constructor. When printing all the instructions .ToString() I also cannot seem to see anything in the IL - I do see the numbered parameter as !!0, but that doesn't help if I can't resolve it to a type or to the factory method.
Does anyone have any ideas on how to solve this?
Most likely your code is looking in the wrong place.
C# compiler will try to cache the conversion of lambda expression -> delegate.
if you look in sharplab.io you'll see that the compiler is emitting an inner class '<>c' inside your Foo class and in that class it emits the method '<Bar>b__0_0' that will be passed as the delegate (see opcode ldftn).
I don't think there's an easy, non fragile way to find that method.
That said, one option would be to:
Find the AddSingleton() method call
From there start going back to the previous instructions trying to identify which one is pushing the value consumed in 1 (the safest way to do that would be to consider how each instruction you are visiting changes the stack). In the code I've linked, it would be IL_0021 (a dup) of Bar() method.
From there, do something similar to 2, but now looking for the instruction that pushes the method reference (a ldftn) used by the ctor of Func<T, R>; in the code linked, it would be IL_0016.
Now you can inspect the body (in the code linked, Foo/'<>c'::'<Bar>b__0_0')
Note that this implementation has some holes though; for instance, if you call AddSingleton() with a variable/parameter/field as I've done (services.AddSingleton(_func);) you'll need to chase the initialization of that to find the referenced method.
Interestingly, at some point Cecil project did support flow analysis (https://github.com/mono/cecil-old/tree/master/flowanalysis).
If you have access to the source code, I think it would be easier to use Roslyn to analyze it (instead of analyzing the assembly).
Recently i tried to create a MVC application using ASP.NET Core 2.0 and i had some values defined in appsettings.json,
"MySettings": {
"WebApiBaseUrl": "http://localhost:6846/api/"
}
In order to read these values i have added
services.Configure<MySettingsModel>(Configuration.GetSection("MySettings"));
above line in ConfigureServices method in Startup.cs
and in my home controller i have added
private readonly IOptions<MySettingsModel> appSettings;
public HomeController(IOptions<MySettingsModel> app)
{
appSettings = app;
}
MySettingsModel class is just a model with property same as key define in appsettings.json.
by this method i'm able to read the value of this key.
Now my issue is that i want to use this key in many controllers so i don't want to repeat this code in every controller so what i did was i created a BaseConntroller, added its constructor and i got my values there. But when i inherit other controllers with my BaseController , it throws me an error and tells me to generate it's constructor, so basically it tells me to add constructor in every controller which is what i wanted to avoid.
How can i achieve this?
You can see the image for the error
And these are the potential fixes that it shows me.
This is just basic C# inheritance. Derived classes must re-implement constructors on base classes (at least the ones you want or need). The only exception is the empty constructor, which is implicit. In other words, you simply need:
public class HomeController : BaseController
{
public HomeController(IOptions<MySettingsModel> app)
: base(app)
{
}
And, of course, you need to change the accessibility of the base class field to protected instead of private. Otherwise, derived classes will not be able to access it.
Of course, this doesn't really save you that much. However, there's no free lunch here. Like I said, this is a limitation of C#, itself, so you have no choice. Although, it's worth mentioning, that while this can sometimes be annoying, it's actually a kind of useful feature of C#. You can look at any class and see exactly what constructors it has available, without having to trace down all its ancestors.
Actually, there is a good solution here:
https://stackoverflow.com/a/48886242/2060975
I am mostly using this method.
[Authorize]
[ApiController]
public abstract class ApiControllerBase : ControllerBase
{
private IOptions<AppSettings> _appSettings;
protected IOptions<AppSettings> appSettings => _appSettings ?? (_appSettings = (IOptions<AppSettings>)this.HttpContext.RequestServices.GetService(typeof(IOptions<AppSettings>)));
...
}
I hope it helps someone:)
I am trying to use the Unity event aggregator to do messaging between various parts of an application. Currently, this is the only feature of the Prism framework that I would like to use. I am having some trouble understand basic concepts I think.
My goal is in some places to be able to broadcast a certain event, and then pick that event up in other places. The code that I have found to do that requires access to the Unity Container, which from what I can tell requires configuration in a bootstrapper and the bootstrapper needs to instantiate the window. This seems like a lot of extra hoops to jump through in my situation of just wanting to use the event aggregator.
Can somebody point me in the right direction for the bare minimum code to use the event aggregator and nothing else from Prism?
It turns out all that needs to be done is instantiate an instance of the EventAggregator class that prism provides. No container needed. I did it in a singleton. Here's the code I used:
public class MyEventAggregator
{
private static MyEventAggregator instance = new MyEventAggregator();
public static MyEventAggregator GetInstance()
{
return instance;
}
private EventAggregator _Aggregator;
public EventAggregator Aggregator
{
get
{
return _Aggregator;
}
}
private MyEventAggregator()
{
_Aggregator = new EventAggregator();
}
}
You do not need to initialize your Unity Container in your bootstrapper and the bootstrapper is not required to instantiate the window. You can initialize your Unity container in any class you want. The only problem is to spread the Unity instance over your application to have an accessible reference where it is needed.
Let's consider this page's code-behind:
public partial class Products : Page
{
private static SomeClass SharedField;
public Product()
{
// ... Some logic
}
}
Do all Products pages instances share the same SharedField, I know this is a basic concept of static fields. But in this case, really? all users can have access (and can't have their own instance of) to the same static field on the website-level?
If so, in what aspects this would used by the web developer? or is this non-recommended practice?
Yes, there will be a single instance of that static field for all users, but only within a single worker process. If you have web farms/web gardens, they will each have their own static instance. If the worker process restarts, you'll get a new static instance.
You'll have to use locking around that shared field to ensure thread safety.
As for why to use that, I'm not sure, I never do it. The best example I can give you is the built-in static HttpContext.Current, which gives you access to the Request, Response, etc.
SharedField will be available in one instance for the entire life-cycle of the web site.
To read a bit more about it, see this answer.
A better practice would be to store your object in the Application state.
Application["MyObject"] = new SomeClass();
I'm setting up a functional test suite for an application that loads an external configuration file. Right now, I'm using flexunit's addAsync function to load it and then again to test if the contents point to services that exist and can be accessed.
The trouble with this is that having this kind of two (or more) stage method means that I'm running all of my tests in the context of one test with dozens of asserts, which seems like a kind of degenerate way to use the framework, and makes bugs harder to find. Is there a way to have something like an asynchronous setup? Is there another testing framework that handles this better?
It is pretty easy, but took me 2 days to figure it out.
The solution:
First you need to create a static var somewhere.
public static var stage:Stage
There is a FlexUnitApplication.as created by the flexunit framework, and at the onCreationComplete() function, you can set the stage to the static reference created previously:
private function onCreationComplete():void
{
var testRunner:FlexUnitTestRunnerUIAS=new FlexUnitTestRunnerUIAS();
testRunner.portNumber=8765;
this.addChild(testRunner);
testStageRef.stage=stage //***this is what I've added
testRunner.runWithFlexUnit4Runner(currentRunTestSuite(), "testsuitename");
}
and when you would access the stage in the program, you should replace it to:
if(stage==null) stage=testStageRef.stage
Assuming you're using FlexUnit 4, addAsync can be called from a [BeforeClass] method:
public class TestFixture
{
[BeforeClass]
public static function fixtureSetup() : void
{
// This static method will be called once for all the tests
// You can also use addAsync in here if your setup is asynchronous
// Any shared state should be stored in static members
}
[Test]
public function particular_value_is_configured() : void
{
// Shared state can be accessed from any test
Assert.assertEquals(staticMember.particularValue, "value");
}
}
Having said that, testing code that accesses a file is really an integration test. I'm also hardly in a position to argue against using ASMock :)
Sounds like you need to remove the dependency of loading that external file. Pretty much all Aysnchronous tests can be removed through the use of a mocking frameworks. ASMock is an awesome choice for Flex. It will allow you to fake the URLoader object and return faked configurations to run your tests against. Mocking will help with you write much better unit tests as you can mock all dependencies synchronous or asynchronous.