I want an embedded view to be able to call a function from the parent view, so I'm trying to have the child reference its parent by injection. This seems to work fine as long as the embedded view is created onDock:
class TestView : View() {
override val root = vbox {
label("Parent Label")
}
init {
println("Parent is instantiating.")
}
override fun onDock() {
val child = find(TestView2::class)
root.add(child)
}
fun doThing() {
println("Parent is doing a thing.")
}
}
class TestView2 : View() {
val parentClass: TestView by inject()
override val root = hbox {
label("Sub-view label 1")
label("Sub-view label 2")
}
init {
println("Sub-view is instantiating.")
parentClass.doThing()
}
}
I'd like it to be cleaner though. I'd prefer it if I was able to use the find function while creating the parent root. That's a problem, as calling the child view within any part of the init process creates a circular instantiation loop. Any way to avoid this or will I just have to settle for onDock and deal with it?
EDIT:
Just to note, I tried the onDock method again in a real, more complicated application and I got a cycle detection error. So even that method is not guaranteed to work.
You can create cyclic dependencies, but you can't call functions in both component's init block, as that would be impossible to resolve. The main takeaway here is that you're probably doing something you shouldn't. Views should not communicate with each other directly. This creates a tight coupling and prevents reuse. Instead you should communicate with one of the following:
State from a ViewModel
Controller function calls
Events using the EventBus
Since your code example is made up, it's not known what exactly you're trying to achieve in your actual app, but you will find the correct approach in the list above.
I see the urge to call functions in views and setting data directly into ui components instead of using bindings a lot, and in absolutely every case there is a much better way to solve the problem :)
Related
I'm trying to write a Jasmine test for a function of class which instantiates and observes an object from another class. Since I want to keep this test contained to the first class and to simulate different scenarios of the second I want to mock the second. Some pseudo code might help
export class Foo {
startProcessing() {
const bar = new Bar();
const sub = bar.tickTock.subscribe(
state => {
// something went right
},
error => {
// something went wrong
}
);
}
}
I've tried declaring the mock class in my test file, and providing it through TestBed.configureTestingModule's providers attribute, but it always uses the original Bar.
How can I write a test that provides a mock class in place of Bar that I can control?
One way to get around this issue is to pass in object of type Bar through function parameter (dependency injection). That way you can have control over Bar object.
Since Xcode 10.1(maybe 10) when I create a Unit test file I don't have calls super.tearDown() and super.setUp() .
I've not seen such changes in release notes.
In documentation https://developer.apple.com/documentation/xctest/xctestcase/understanding_setup_and_teardown_for_test_methods are still here.
So my question should I still write super.tearDown() and super.setUp()?
class SomethingTests: XCTestCase {
override func setUp() {
// Put setup code here. This method is called before the invocation of each test method in the class.
}
override func tearDown() {
// Put teardown code here. This method is called after the invocation of each test method in the class.
}
func testExample() {
// This is an example of a functional test case.
// Use XCTAssert and related functions to verify your tests produce the correct results.
}
func testPerformanceExample() {
// This is an example of a performance test case.
self.measure {
// Put the code you want to measure the time of here.
}
}
}
For a direct subclass of XCTestCase, there never was any change of behavior for not calling super.setUp(). That's because setUp and tearDown are template methods with empty implementations at the top level.
Though there's no change in behavior, omitting the calls to super means that if you create a test hierarchy with more than one level, you'll have to add them back.
When would you ever have more than one level? There are two cases:
When you want to reuse the same tests for different scenarios.
When you subclass XCTestCase to make a customized helper.
These don't happen every day. But they do happen. Deciding "I need it here, but I don't need it there" is perilous. So I'd just call super all the time.
Here is my problem:
Aurelia app:
a few custom elements (already sharing a view via #UseView) doing almost the same thing (specific func shoud be defined by every element itself), how to manage shared code (inkl #bindable)?
How to refactor this:
https://gist.run/?id=897298ab1dad92fadca77f64653cf32c
The "shared" code you refer to in your question is lifecycle-related stuff in your custom elements, which isn't really suited for sharing. You would need to do inheritance, and with custom elements that's setting yourself up for a lot of headaches.
Rather than sharing code, why not focus on the things which are variable and try to make them configurable? By looking at your gist, that seems by far the most straightforward solution here.
Say you have a custom element that calls a function when a property changes. This function needs to be different for some instances of the element. You could accomplish that with a bindable function, and use the .call behavior, like so:
some-element.js
import { bindable } from 'aurelia-framework';
export class SomeElement {
#bindable value;
#bindable processValue;
valueChanged(newValue, oldValue) {
if (this.processValue) {
this.processValue({ val: newValue });
}
}
}
consumer.html
<some-element value.bind="myValue" process-value.call="myFunc(val)"></some-element>
<some-element value.bind="anotherValue" process-value.call="anotherFunc(val)"></some-element>
consumer.js
myFunc(val) {
console.log("val: " + val);
}
anotherFunc(val) {
console.log("val: " + val);
}
This seems to be a problem that comes up a lot. I've been coming up with the same solution nearly every time but was curious if people have a better method of accomplishing this.
I have one class that is a list of instances of another class. The state of the parent class is dependent upon state of ALL the children
As an example. Say I have the following classes
class Box
{
int _objectId= <insert_unique_id>;
int _itemCount = 0;
public void AddItem()
{
_itemCount = Max(_itemCount + 1, 5);
}
public int GetId()
{
return _objectId;
}
public bool IsFull()
{
return _itemCount == 5
}
}
class BiggerBox
{
Map<int, Box> _boxes;
public void AddToBox(int id)
{
_boxes[id].AddItem();
}
public bool IsFull()
{
foreach(var box in _boxes.Values)
if(!box.IsFull())
return false;
return true;
}
}
All additions to a "Box" are done via the BiggerBox.AddToBox call. What I would like to do is be able to determine box.IsFull() without iterating over every single item every time we add an element.
Typically i accomplish this by keeping a SET or a separate collection of what items are full.
Curious, has anyone come up to an ingenious solution to this or is the simple answer that there is no other way?
There are two things you need to do in order to accomplish what you want:
Be able to control every entrypoint to your collection
React to changes to the objects in the collection
For instance, if the objects in the collection are mutable (meaning, they can change after being added to your collection) you need your main object to react to that change.
As you say, you could create a separate set of the objects that are full, but if the objects can change afterwards, when they change you either need to take them out of that set, or add them to it.
This means that in order for you to optimize this, you need some way to observe the changes to the underlying objects, for instance if they implement INotifyPropertyChanged or similar.
If the objects cannot change after being added to your main object, or you don't really care if they do, you just need to control every entrypoint, meaning that you basically need to add the necessary checks to your AddItem method.
For your particular types I would implement an event on the Box class so that when it is full, it fires the event. Your BiggerBox class would then hook into this event in order to observe when an underlying box becomes full.
You can upkeep the number of complete (or non-complete) boxes in BiggerBox class, and update it in all the functions.
E.g., in AddToBox it could be:
bool wasFull = _boxes[id].IsFull;
_boxes[id].AddItem();
if (!wasFull && _boxes[id].IsFull) // After this update box has become full.
completeBoxes += 1;
It is also possible to implement this upkeep procedure in other hypothetical functions (like RemoveFromBox, AddBox, RemoveBox, etc.)
Is there a way to pass data to dependencies registered with either Execution Context Scope or Lifetime Scope in Simple Injector?
One of my dependencies requires a piece of data in order to be constructed in the dependency chain. During HTTP and WCF requests, this data is easy to get to. For HTTP requests, the data is always present in either the query string or as a Request.Form parameter (and thus is available from HttpContext.Current). For WCF requests, the data is always present in the OperationContext.Current.RequestContext.RequestMessage XML, and can be parsed out. I have many command handler implementations that depend on an interface implementation that needs this piece of data, and they work great during HTTP and WCF scoped lifestyles.
Now I would like to be able to execute one or more of these commands using the Task Parallel Library so that it will execute in a separate thread. It is not feasible to move the piece of data out into a configuration file, class, or any other static artifact. It must initially be passed to the application either via HTTP or WCF.
I know how to create a hybrid lifestyle using Simple Injector, and already have one set up as hybrid HTTP / WCF / Execution Context Scope (command interfaces are async, and return Task instead of void). I also know how to create a command handler decorator that will start a new Execution Context Scope when needed. The problem is, I don't know how or where (or if I can) "save" this piece of data so that is is available when the dependency chain needs it to construct one of the dependencies.
Is it possible? If so, how?
Update
Currently, I have an interface called IProvideHostWebUri with two implementations: HttpHostWebUriProvider and WcfHostWebUriProvider. The interface and registration look like this:
public interface IProvideHostWebUri
{
Uri HostWebUri { get; }
}
container.Register<IProvideHostWebUri>(() =>
{
if (HttpContext.Current != null)
return container.GetInstance<HttpHostWebUriProvider>();
if (OperationContext.Current != null)
return container.GetInstance<WcfHostWebUriProvider>();
throw new NotSupportedException(
"The IProvideHostWebUri service is currently only supported for HTTP and WCF requests.");
}, scopedLifestyle); // scopedLifestyle is the hybrid mentioned previously
So ultimately unless I gut this approach, my goal would be to create a third implementation of this interface which would then depend on some kind of context to obtain the Uri (which is just constructed from a string in the other 2 implementations).
#Steven's answer seems to be what I am looking for, but I am not sure how to make the ITenantContext implementation immutable and thread-safe. I don't think it will need to be made disposable, since it just contains a Uri value.
So what you are basically saying is that:
You have an initial request that contains some contextual information captured in the request 'header'.
During this request you want to kick off a background operation (on a different thread).
The contextual information from the initial request should stay available when running in the background thread.
The short answer is that Simple Injector does not contain anything that allows you to do so. The solution is in creating a piece of infrastructure that allows moving this contextual information along.
Say for instance you are processing command handlers (wild guess here ;-)), you can specify a decorator as follows:
public class BackgroundProcessingCommandHandlerDecorator<T> : ICommandHandler<T>
{
private readonly ITenantContext tenantContext;
private readonly Container container;
private readonly Func<ICommandHandler<T>> decorateeFactory;
public BackgroundProcessingCommandHandlerDecorator(ITenantContext tenantContext,
Container container, Func<ICommandHandler<T>> decorateeFactory) {
this.tenantContext = tenantContext;
this.container = container;
this.decorateeFactory = decorateeFactory;
}
public void Handle(T command) {
// Capture the contextual info in a local variable
// NOTE: This object must be immutable and thread-safe.
var tenant = this.tenantContext.CurrentTenant;
// Kick off a new background operation
Task.Factory.StartNew(() => {
using (container.BeginExecutionContextScope()) {
// Load a service that allows setting contextual information
var context = this.container.GetInstance<ITenantContextApplier>();
// Set the context for this thread, before resolving the handler
context.SetCurrentTenant(tenant);
// Resolve the handler
var decoratee = this.decorateeFactory.Invoke();
// And execute it.
decoratee.Handle(command);
}
});
}
}
Note that in the example I make use of an imaginary ITenantContext abstraction, assuming that you need to supply the commands with information about the current tenant, but any other sort of contextual information will obviously do as well.
The decorator is a small piece of infrastructure that allows you to process commands in the background and it is its responsibility to make sure all the required contextual information is moved to the background thread as well.
To be able to do this, the contextual information is captured and used as a closure in the background thread. I created an extra abstraction for this, namely ITenantContextApplier. Do note that the tenant context implementation can implement both the ITenantContext and the ITenantContextApplier interface. If however you define the ITenantContextApplier in your composition root, it will be impossible for the application to change the context, since it does not have a dependency on ITenantContextApplier.
Here's an example:
// Base library
public interface ITenantContext { }
// Business Layer
public class SomeCommandHandler : ICommandHandler<Some> {
public SomeCommandHandler(ITenantContext context) { ... }
}
// Composition Root
public static class CompositionRoot {
// Make the ITenantContextApplier private so nobody can see it.
// Do note that this is optional; there's no harm in making it public.
private interface ITenantContextApplier {
void SetCurrentTenant(Tenant tenant);
}
private class AspNetTenantContext : ITenantContextApplier, ITenantContext {
// Implement both interfaces
}
private class BackgroundProcessingCommandHandlerDecorator<T> { ... }
public static Container Bootstrap(Container container) {
container.RegisterPerWebRequest<ITenantContext, AspNetTenantContext>();
container.Register<ITenantContextApplier>(() =>
container.GetInstance<ITenantContext>() as ITenantContextApplier);
container.RegisterDecorator(typeof(ICommandHandler<>),
typeof(BackgroundProcessingCommandHandlerDecorator<>));
}
}
A different approach would be to just make the complete ITenantContext available to the background thread, but to be able to pull this off, you need to make sure that:
The implementation is immutable and thus thread-safe.
The implementation doesn't require disposing, because it will typically be disposed when the original request ends.