如何通知事件的类组件？

Question

我有一个名为A的类,它的组件类叫做B.

public class A {
    B myB;

    ...
    public void bWasUpdated(){
       ...
        List<String> list = myB.connections;
    }
}

如果我的A类中有B的实例,并且如果B的实例以某种方式更新,那么如何通知我的A类实例并调用bWasUpdated()？

我试过接口但最终真的很困惑.我想我不太明白如何在对象及其组件之间传递数据.

编辑

public class B {
    ArrayList<String> connections;

    ....

    public void listen(){

        ...
        if(foundNewConnection){
            this.connections.add(theNewConnection);
            //Notify class A about this new connection;
        }
    }
}

Answer 1

您应该使用一个Listener,它是一种称为Observer模式的模式.

首先,将此接口添加到B类:

public interface ChangeListener {
    public void onChangeHappened();
}

其次,使用setter将侦听器变量添加到B:

private ChangeListener listener;

public void setChangeListener(ChangeListener listener) {
    this.listener = listener;
}

第三,使A实现ChangeListener接口并将其自身注册为侦听器:

public class A implements ChangeListener {

public A() {
    myB = new B();
    myB.setChangeListener(this);
}

...

public void onChangeHappened() {
    // do something with B now that you know it has changed.
}

最后但并非最不重要的是,当事情发生变化时,请在B内部召唤听众:

public void someMethodInB() {
    // change happened
    if (listener != null) {
        listener.onChangeHappened();
    }
}