[英]How do I notify a class component of an event?
I have class named A and its component class called B. 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;
}
}
If I have an instance of B in my class A and if that instance of B gets updated somehow, how can I notify my instance of class A and call bWasUpdated()
? 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()
?
I tried interfaces but ended up really confused. 我试过接口但最终真的很困惑。 I guess I don't quite understand how to pass data yet between an object and its component.
我想我不太明白如何在对象及其组件之间传递数据。
EDIT 编辑
public class B {
ArrayList<String> connections;
....
public void listen(){
...
if(foundNewConnection){
this.connections.add(theNewConnection);
//Notify class A about this new connection;
}
}
}
You should use a Listener , which is a form of the pattern called the Observer pattern . 您应该使用一个Listener ,它是一种称为Observer模式的模式 。
First, add this interface to your B class: 首先,将此接口添加到B类:
public interface ChangeListener {
public void onChangeHappened();
}
Second, add a listener variable to B with a setter: 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;
}
Third, make A implement the ChangeListener interface and register itself as a listener: 第三,使A实现ChangeListener接口并将自己注册为监听器:
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.
}
And last but not least, call your listener inside B when something changes: 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();
}
}
如果B - A的内部类,则可以在B setter(或其他状态修饰符)中调用A.this.bWasUpdated();
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