The Async pipe not trigger even when getter of observable is called

Question

I have a question. Maybe one of you can help me. I have a situation when async pipe in component not trigger even then subscribition get of this observable is triggering (component not reviving changed value in ngOnChanges).

Code is like this:

html:

<app-component [values]="values$ | async"></app-component>

ts:

values$: Observable<ISomeValue[]> = this.service.getValue$();

service:

private valuesBSubject: BehaviorSubject<ISomeValue[]> = new BehaviorSubject<ISomeValue[]>(this.defaultValues);

getValues$(): Observable<ISomeValue[]> {
        return this.valuesBSubject.asObservable();
    }

setValues(values: ISomeValue[]): void {
        this.valuesBSubject.next(values);
    }

Answer 1

You can't do that using member functions. However, you can do that using a generic function (or an algorithm). As your members are private, you'll need to make the algorithm a friend, though:

#include <iostream>
#include <vector>

template <typename T> void print(T const&);
template <typename T> void addNum(T&, int);

class Base 
{
    template <typename T> friend void print(T const&);
    template <typename T> friend void addNum(T&, int);

private:
    std::vector<int> nums;
};

class Derived : public Base 
{
    template <typename T> friend void print(T const&);
    template <typename T> friend void addNum(T&, int);
private:
    std::vector<int> nums;
};


template <typename T>
void print(T const& obj) {
    for (auto x: obj.nums) {
        std::cout << x << " ";
    }
    std::cout << "\n";
}

template <typename T>
void addNum(T& obj, int num) {
     obj.nums.push_back(num);
}

int main()
{
    Base b;
    addNum(b, 1);
    addNum(b, 2);
    print(b);

    Derived d;
    addNum(d, 3);
    addNum(d, 4);
    addNum(static_cast<Base&>(d), 5);
    print(static_cast<Base&>(d));
    print(d);
}

I don't necessarily think that an approach like that is well-advised. However, it is certainly doable. A variation of a similar idea is to actually access the nums container through a virtual function, yielding the respective version of the corresponding derived class:

class Base 
{   
private:
    std::vector<int> d_nums;
    virtual std::vector<int> &nums() { return this->d_nums; }
public:
    void addNum(int num) { nums().push_back(num); }
};  

class Derived : public Base 
{   
private:
    std::vector<int> nums;
    std::vector<int> &nums() override { return this->d_nums; }
};