Java Observer Update功能 [英] Java Observer Update function

问题描述

我有一个实现观察者的类，当然它需要具有更新功能：

I have a class that implements observer, and of course it needs to have the update function:

public void update(Observable obs, Object obj);

有人可以解释这两个参数代表什么？
Observable当然是我的可观察对象，但是，如何通过这个Observable obs对象访问我的可观察字段？
什么是对象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?

推荐答案

如果其他人在确定如何发送第二个时遇到困难参数，就像尼克指出的那样：在 notifyObservers 方法调用中。

In case anybody else is experiencing difficulty in figuring out how to send that second parameter, it is as Nick points out: In the notifyObservers method call.

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
}

在观察者：

@Override
public void update(Observable obs, Object arg) {
    if (obs instanceof QlmLicense) {
        setValid((Boolean) arg);
    }
}

确保正确连接Observable ，否则你的更新方法不会被调用。

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);
        }
    }
}

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