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How can we implement observer pattern in .NET?


By : Joann
Date : October 17 2020, 11:12 PM
To fix this issue In .NET architecture,there are lot of design patterns.I want to know about what is meant with observer pattern and how it is implemented , The Observer pattern is pretty much reified in C# as events.
code :


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Observer: Implement with pattern (subject & observer) or inter-thread communication (wait & notify)


By : Ms_Terree
Date : March 29 2020, 07:55 AM
will help you You are comparing apples and oranges. The wait/notify mechanism is used for thread synchronization, and while your colleague may have used it within an Observer/Observable implementation, it is not, in itself the pattern implementation. It simply means it is a multithreaded implementation.
There are many implementations of this pattern, and they are typically tailored to the environment in which you are working. There are event mechanisms built into most UI frameworks/toolkits. JMS for distributed environments, ...

Can one class implement both subject and observer sections of the observer design pattern?


By : jw382
Date : March 29 2020, 07:55 AM
I hope this helps . I think one of these would be slightly more appropriate to use than observer pattern, depending on actually how you want to implement your framework:
Implicit Invocation Event-Driven Publish-Subscribe

Implement Observer Pattern in C++


By : Dima Stos
Date : March 29 2020, 07:55 AM
I wish this helpful for you I don't believe there is a way to implement the Observer pattern in C++ using just reflection. If you don't use any external tools, you have to implement everything manually. For instance, I'd implement it something like:
code :
#include <iostream>
#include <set>
using namespace std;

class Impl;

class ObserverBase {
public:
    virtual void propertyChanged(Impl *impl, int value) = 0;
};

class Impl {
public:
    void setProperty(int value) {
        if (m_property != value) {
            m_property = value;
            for(auto observer:m_observers) {
                observer->propertyChanged(this, value);
            }
        }
    }
    int getProperty() {
        return m_property;
    }

    void addObserver(ObserverBase *observer) {
        m_observers.insert(observer);
    }
private:
    int m_property;
    set<ObserverBase *> m_observers;
};

class Observer : public ObserverBase {
public:
    virtual void propertyChanged(Impl *impl, int value) {
        cout << "Saw new value of " << value << "!" << endl;
    }
};

int main() {
    Impl impl;
    impl.addObserver(new Observer());
    impl.setProperty(5);
}

How to implement the Observer pattern in JNI


By : Dharampal Rana
Date : March 29 2020, 07:55 AM
wish helps you It took me forever to implement this solution. I had to pull information from all over the internet. Here it is:
code :
//Optional, this is just so that I can retrieve the C++ MyLibrary instance
//easily from the Java.
JNIEXPORT void JNICALL Java_MyLibrary_initCpp(JNIEnv* env, jobject javaMyLibrary) {
    //Save the C++ version of MyLibrary as a field inside the Java MyLibrary.
    MyLibrary * lib = new MyLibrary();
    env->SetLongField(javaMyLibrary, CPP_MYLIBRARY_POINTER_FIELD, ptr_to_jlong(lib));
}

JNIEXPORT void JNICALL Java_MyLibrary_setObserver(JNIEnv* env, 
        jobject javaMyLibrary, jobject javaObserver) {
    //Retrieve the CPP version of MyLibrary. For me, I stored it inside the java
    //object as a field, but you can implement it any way you want.
    MyLibrary* cppMyLibrary = (MyLibrary*)jlong_to_ptr(
        env->GetLongField(javaMyLibrary, CPP_MYLIBRARY_POINTER_FIELD));
    if (cppMyLibrary == NULL) {
        //Handle the problem
        return;
    }
    jthrowable exc = NULL;

    //Keep the jvm object around; the env is not available in another thread
    //but can be obtained from the jvm.
    JavaVM* jvm;
    env->GetJavaVM(&jvm);

    //The observer has to be made global; it's not available in another thread.
    jobject observer = env->NewGlobalRef(javaObserver);
    //TODO: retrieve the previous observer and clean it up with DeleteGlobalRef()
    //TODO: clean up this observer when destroying MyLibrary with DeleteGlobalRef()

    try {
        //At this point, both "jvm" and "observer" are accessible from the other thread.
        cppMyLibrary->setLogFunction([jvm, observer] (std::string& p0, std::string& p1) {
            JNIEnv* env;
            jvm->AttachCurrentThread(&env, NULL); //Obtain the env
            jclass clazz = env->GetObjectClass(observer);
            jmethodID meth = env->GetMethodID(clazz, "log",
                    "(Ljava/lang/String;Ljava/lang/String;)V");
            jstring s0 = env->NewStringUTF(p0.c_str());
            jstring s1 = env->NewStringUTF(p1.c_str());
            env->CallVoidMethod(observer, meth, s0, s1);

            //TODO: make sure this is called even if there's an exception!
            jvm->DetachCurrentThread();
        });
    } catch (...) {
        exc = //handle your exceptions here
    }

    if (exc != NULL) {
        env->Throw(exc);
    }
}

How do I implement the Observer pattern in this MVC pattern program


By : Jason
Date : March 29 2020, 07:55 AM
should help you out Usually the model is the subject (Observable). The idea is: you can change the model from different places (controllers) and all other ones (that subscribed for changes) will be notified. So the controllers are Observers. In this particular example you can implement the Observer pattern to remove the
code :
controller.updateView();
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