i've a problem related to view models.
I need to access the method of this viewModel:
class TheacerViewModel{
Teacher _teacherX;
TeacherViewModel(Teacher teacherX): _teacherX = teacherX;
String get name{
return _teacherX.name;
}
String get surname{
return _teacherX.surname;
}
int get age{
return _teacherX.age;
}
}
into this viewModel:
class CourseViewModel{
Course _courseX;
CourseViewModel(Course courseX): _courseX = courseX;
String get subject{
return _courseX.subject;
}
/*
my solution (not working)
Teacher get teacher{
return _courseX.theacer;
}
*/
}
My solution not working.
It is possible to do this thing ?
I've already create Teacher and Course model.
Thanks.
for #towhid comment
now i have to update this part of code(maybe only the last line)and add "teacher: teacher" to CourseViewModel(...), but how ?
because courses.map does not allow me to add 2 parameters.
List<CourseViewModel> coursesL = List<CourseViewModel>();
void courses() async {
List<Course> courses = await WebService().fetchCourses();
notifyListeners();
this.coursesL = courses.map((courseX) => CourseViewModel(courseX: courseX)).toList();
An ideal approach would be creating the independent ViewModel first and then pass that instance to the dependent ViewModels constructor to use its method and properties. This way, you can avoid of creating any unnecessary instances.
class CourseViewModel{
Course _courseX;
Teacher _teacher;
CourseViewModel(Course courseX, Teacher teacher): _courseX = courseX, _teacher = teacher;
String get subject{
return _courseX.subject;
}
Teacher get teacher => _teacher;
}
Related
class ExampleClass {
//default constructor
ExampleClass() {
//do stuff
}
//named constructor
ExampleClass.namedConstructor() {
//do stuff
}
}
void main() {
//is there a way to create a variable with datatype to store an object that is constructed only with a specific constructor?
//I have tried something like this, but it returns an error
ExampleClass.namedConstructor variable_1;
}
Is there any way to do this or an alternative? because I need to be able to differentiate between an object that is constructed with the default constructor or with a named constructor.
You can add some identification to classes builded with different constructors and compare entities by unique parameters.
If instances of your classes creating once (Singleton design pattern), you can create entities as constants and compare it by reference:
const administrator = User.administrator();
class User {
final int id;
User(this.id);
factory User.administrator() {
return User(0);
}
factory User.administrator(int id) {
return User(id);
}
}
I need to recollect some data calling to a method is connecting to a webservice.
problem: Imagine I need to update the content text of a label control according to this remote gathered information. Until all this data is recollected I'm not going to be able to show the label.
desired: I'd like to first show the label with a default text, and as I'm receiving this information I want to update the label content (please, don't take this description as a sucked code, I'm trying to brief my real situation).
I'd like to create an observable sequence of these methods. Nevertheless, these method have not the same signature. For example:
int GetInt() {
return service.GetInt();
}
string GetString() {
return service.GetString();
}
string GetString2 {
return service.GetString2();
}
These methods are not async.
Is it possible to create an observable sequence of these methods?
How could I create it?
Nevertheless, which's the best alternative to achieve my goal?
Creating custom observable sequences can be achieved with the Observable.Create. An example using your requirements is shown below:
private int GetInt()
{
Thread.Sleep(1000);
return 1;
}
private string GetString()
{
Thread.Sleep(1000);
return "Hello";
}
private string GetString2()
{
Thread.Sleep(2000);
return "World!";
}
private IObservable<string> RetrieveContent()
{
return Observable.Create<string>(
observer =>
{
observer.OnNext("Default Text");
int value = GetInt();
observer.OnNext($"Got value {value}. Getting string...");
string string1 = GetString();
observer.OnNext($"Got string {string1}. Getting second string...");
string string2 = GetString2();
observer.OnNext(string2);
observer.OnCompleted();
return Disposable.Empty;
}
);
}
Note how I have emulated network delay by introducing a Thread.Sleep call into each of the GetXXX methods. In order to ensure your UI doesn't hang when subscribing to this observable, you should subscribe as follows:
IDisposable subscription = RetrieveContent()
.SubscribeOn(TaskPoolScheduler.Default)
.ObserveOn(DispatcherScheduler.Current)
.Subscribe(text => Label = text);
This code uses the .SubscribeOn(TaskPoolScheduler.Default) extension method to use a TaskPool thread to start the observable sequence and will be blocked by the calls the Thread.Sleep but, as this is not the UI thread, your UI will remain responsive. Then, to ensure we update the UI on the UI thread, we use the ".ObserveOn(DispatcherScheduler.Current)" to invoke the updates onto the UI thread before setting the (data bound) Label property.
Hope this is what you were looking for, but leave a comment if not and I'll try to help further.
I would look at creating a wrapper class for your service to expose the values as separate observables.
So, start with a service interface:
public interface IService
{
int GetInt();
string GetString();
string GetString2();
}
...and then you write ServiceWrapper:
public class ServiceWrapper : IService
{
private IService service;
private Subject<int> subjectGetInt = new Subject<int>();
private Subject<string> subjectGetString = new Subject<string>();
private Subject<string> subjectGetString2 = new Subject<string>();
public ServiceWrapper(IService service)
{
this.service = service;
}
public int GetInt()
{
var value = service.GetInt();
this.subjectGetInt.OnNext(value);
return value;
}
public IObservable<int> GetInts()
{
return this.subjectGetInt.AsObservable();
}
public string GetString()
{
var value = service.GetString();
this.subjectGetString.OnNext(value);
return value;
}
public IObservable<string> GetStrings()
{
return this.subjectGetString.AsObservable();
}
public string GetString2()
{
var value = service.GetString2();
this.subjectGetString2.OnNext(value);
return value;
}
public IObservable<string> GetString2s()
{
return this.subjectGetString2.AsObservable();
}
}
Now, assuming that you current service is called Service, you would write this code to set things up:
IService service = new Service();
ServiceWrapper wrapped = new ServiceWrapper(service); // Still an `IService`
var subscription =
Observable
.Merge(
wrapped.GetInts().Select(x => x.ToString()),
wrapped.GetStrings(),
wrapped.GetString2s())
.Subscribe(x => label.Text = x);
IService wrappedService = wrapped;
Now pass wrappedService instead of service to your code. It's still calling the underlying service code so no need for a re-write, yet you still are getting the observables that you want.
This is effectively a gang of four decorator pattern.
I want to fetch the categories with products and images. I have following relation:
Product Model
class Product extends Model
{
public function productCategory() {
return $this->belongsToMany('ProductCategory');
}
public function addtionalImages() {
return $this->hasMany('ProductImage');
}
}
Product Category Model
class ProductCategory extends Model
{
public function product() {
return $this->hasMany('Bazar\Models\Product', 'product_catid')
->orderBy('id', 'DESC')->limit(10);
}
}
This is how i am using eager loading:
$categories = ProductCategory::select('product_categories.*')
->with(['product'])->Paginate(20);
This returns the category and products not the additionalImage, images are related to products not with the categories, I tried ->with(['product', 'addtionalImages']) but no success, can anyone let me know what i missed? or how do i achieve?
SOLVED
I solved it, and posting the answer so it helps to others.
$categories = ProductCategory::select('product_categories.*')
->with(['product', 'product.addtionalImages'])->Paginate(20);
With use of product.addtionalImages i can access the methods of related relation.
Portfolio Model:
public function getCats(){
return $this->hasMany(RelPortfolioCategory::class,'portfolioID','id');
}
controller:
public function portfolioDetail($slug){
$db = Portfolio::where('slug' , $slug)->with('getCats')->firstOrFail();
$dbRelated = RelPortfolioCategory::whereIn('categoryID' , $db->getCats->pluck('categoryID'))->whereNot('portfolioID' , $db->id)
->with('getPortfolioDetail')->get();
return view('portfolioDetail' , compact('db' , 'dbRelated'));
}
Given an arbitrary field on a Java object, I want to create an Observable that will watch that field and push a new result to an Observer every time the value of the field changes. ReactiveCocoa has a macro called RACObserve, which appears to do exactly this.
I want to know how to implement similar functionality using RxJava.
For example, say I had the following simple class:
public class Foo {
enum State {
Idle,
Ready,
Error
}
private State currentState = State.Idle;
//methods that can change currentState
}
I want to create an Observable<State> that will push the new state to an Observer every time something changes the value of currentState.
In ReactiveCocoa, it looks like I would write something sort of like the following (please excuse my pseudo Objective-C):
[RACObserve(self, currentState) subscribeNext:^(NSString *newState) {
NSLog(#"%#", newState);
}];
How would I achieve similar functionality in RxJava? I'm thinking that I may need to wrap all changes to currentState in a setter, but it's not clear to me where I should then call Observable.create and how to feed the changes of currentState to an Observer.
ReactiveCocoa is actually more similar to ReactiveUI (http://www.reactiveui.net) than just plain Rx. And in ReactiveUI, you can use this.WhenAnyValue(x => x.PropName) to do exactly what you want.
I stumbled across this same problem recently, I ended up using PropertyChangeListener, which will emit an object when a property is changed, see the following:
Update Listener:
public class GameUpdateListener {
public static Observable<Object> changed(Game game) {
final BehaviorSubject<Object> subject = BehaviorSubject.create((Object)game);
game.addPropertyChangeListener(new PropertyChangeListener() {
#Override
public void propertyChange(PropertyChangeEvent propertyChangeEvent) {
subject.onNext( (Object)propertyChangeEvent.getNewValue());
}
});
return subject;
}
}
Some custom object:
public class Game {
private PropertyChangeSupport pcs = new PropertyChangeSupport(this);
...
public setSomeField(String field){
this.field = field;
pcs.firePropertyChange("field", this.field, field);
}
public void addPropertyChangeListener(PropertyChangeListener propertyChangeListener) {
pcs.addPropertyChangeListener(propertyChangeListener);
}
...
}
Observe:
Game game = new Game();
GameUpdateListener listener = new GameUpdateListener();
final Observable<Object> gameObserver = listener.changed(game);
gameObserver.subscribe(new Action1<Object>() {
#Override
public void call(Object o) {
Log.e(TAG, "Object Changed");
}
});
game.setSomeField("New value");
This will work fine as long as you don't need to instantiate your object again. Perhaps a solution to this is to create a local setter method and emit a change there.
Since your question title contains "or Rx.NET", here is my suggestion (I dunno bout RxJava, you may find something similar).
You probably will have to leverage some sort of mechanism in the setter. The standard way in .NET is by using the INotifyPropertyChanged interface.
Then by firing the events, you can create an IObservable<T> from this stream by using
Observable.FromEvent<TEvent, TArgs>()
You can find a really good example of what you want to do (.NET) here.
(credits to Rob Foncesa-Ensor)
I think what you are after is a Subject<T>. It implements IObserver<T>, so you can call OnNext(T) to fire a new value, as well as IObservable<T>, which you can expose it as publicly so it can be subscribed to.
If you need it to fire the latest value to new subscribers, you can use a ReplaySubject<T> with a buffer size of 1.
Here's a basic implementation:
public class SomeService
{
private Subject<int> values = new Subject<int>();
public IObservable<T> Values
{
get
{
// AsObservable prevents it from being cast back to Subject
return values.AsObservable();
}
}
// Private; called by some internal mechanism
private void SetValue(int newValue)
{
newValue.OnNext(newValue);
}
}
I want to store globally the object User (that is the table USER in my db) in my HomeController, in that way i don't have to instantiate it in every single action.
I found the following solution that works pretty fine
public class HomeController : Controller
{
private DatabaseContext db = new DatabaseContext();
private User currentUser;
private User CurrentUser
{
get
{
if (User.Identity.IsAuthenticated)
//This function returns the object "User" (table USER in db) based on the PK of the table
currentUser = CustomDbFunctions.GetUserEntityFromUsername(User.Identity.Name, db);
return currentUser;
}
}
public ActionResult Index()
{
if (User.Identity.IsAuthenticated)
return View(CurrentUser);
else
return Redirect("login");
}
}
I'd like to know if there's a better (or more elegant) way to achieve the same goal.
Please note that i'm not using the MembershipProvider.
In your example the user object is instantiated in every single action (in contrast to what you said). This is because actions are usually invoked per http request and controller instances are disposed after each use.
Your code shares the instance structurally (you don't have to repeat the code) which is ok but what about sharing the code between different controllers? I'd suggest to refactor your GetUserEntityFromUsername a little bit so that you retrieve the object only once per request, using the Items container to get the request scope:
public class CustomDbFunctions
{
const string itemsUserKey = "_itemsUserKey";
public static User GetUserEntityFromUsername( IPrincipal principal, DatabaseContext db )
{
if ( principal == null || principal.Identity == null ||
!principal.Identity.IsAuthenticated
)
return null;
if ( HttpContext.Current.Items[itemsUserKey] == null )
{
// retrieve the data from the Db
var user = db.Users.FirstOrDefault( u => u.Name == User.Identity.Name );
HttpContext.Current.Items[itemsUserKey] = user;
}
return (User)HttpContext.Current.Items[itemsUserKey];
}
This way your wrapper takes care of retrieving the instance from the database once per request.
Note that this requires sharing your database context as entities should not be reused on different contexts. Fortunately, this can be done in a similar way:
public class CustomDbFunctions
{
const string dbUserKey = "dbUserKey";
public static DatabaseContext CurrentDatabaseContext
{
get
{
if ( HttpContext.Current.Items[dbUserKey] == null )
{
DatabaseContext ctx = new DatabaseContext(); // or any other way to create instance
HttpContext.Current.Items[dbUserKey] = ctx;
}
return (DatabaseContext)HttpContext.Current.Items[dbUserKey];
}
}
This way, the context instance, shared per request, is always available as
CustomDbFunctions.CurrentDatabaseContext