java Java观察者更新功能
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Java Observer Update function
提问by TheNotMe
I have a class that implements observer, and of course it needs to have the update function:
我有一个实现观察者的类，当然它需要具有更新功能：
public void update(Observable obs, Object obj);
Can someone please explain what do the two parameters stand for? Observable is my observable of course, but, how can I access my observable fields through this Observable obs object? And what is Object obj?
有人可以解释一下这两个参数代表什么吗？Observable 当然是我的 observable，但是，如何通过这个 Observable obs 对象访问我的 observable 字段？什么是Object obj？
回答by micha
obsis the object that extends Observableand has the notifyObserversmethod. You can cast obsto your object that extends Observableand then call the methods you need.
objis the optional parameter that can be passed to notifyObservers.
obs是扩展Observable并具有notifyObservers方法的对象。您可以转换obs为扩展的对象，Observable然后调用所需的方法。
obj是可以传递给 的可选参数notifyObservers。
回答by Patricia
In case anybody else is experiencing difficulty in figuring out how to send that second parameter, it is as Nick points out: In the notifyObserversmethod call.
如果其他人在弄清楚如何发送第二个参数时遇到困难，正如尼克指出的那样：在notifyObservers方法调用中。
In the Observable:
在 Observable 中：
private void setLicenseValid(boolean licenseValid) {
this.licenseValid = licenseValid;
setChanged(); // update will only get called if this method is called
notifyObservers(licenseValid); // add parameter for 2nd param, else leave blank
}
In the Observer:
在观察者中：
@Override
public void update(Observable obs, Object arg) {
if (obs instanceof QlmLicense) {
setValid((Boolean) arg);
}
}
Be sure to wire up your Observable correctly, else your update method will not get called.
确保正确连接您的 Observable，否则您的更新方法将不会被调用。
public class License implements Observer {
private static QlmLicense innerlicense;
private boolean valid;
private Observable observable;
private static QlmLicense getInnerlicense() {
if (innerlicense == null) {
innerlicense = new QlmLicense();
// This is where we call the method to wire up the Observable.
setObservable(innerlicense);
}
return innerlicense;
}
public boolean isValid() {
return valid;
}
private void setValid(Boolean valid) {
this.valid = valid;
}
// This is where we wire up the Observable.
private void setObservable(Observable observable) {
this.observable = observable;
this.observable.addObserver(this);
}
@Override
public void update(Observable obs, Object arg) {
if (obs instanceof InnerIDQlmLicense) {
setValid((Boolean) arg);
}
}
}
回答by Nick Robertson
The observer's update(Observable obs,Object obj) method receives through the notifyObservers the object(second parameter) who has changed(in the Observable).
观察者的update(Observable obs,Object obj) 方法通过notifyObservers 接收已经改变的对象（第二个参数）（在Observable 中）。
