用于检测变量更改的 Java 事件侦听器
我似乎无法在任何地方找到我问题的答案。是否有任何事件侦听器可以检测布尔值或其他变量的变化,然后对其进行操作。或者是否可以创建自定义事件侦听器来检测此问题?
请问我似乎在任何地方都找不到解决这个问题的方法,我发现这个网站解释了如何创建自定义事件
我似乎无法在任何地方找到我问题的答案。是否有任何事件侦听器可以检测布尔值或其他变量的变化,然后对其进行操作。或者是否可以创建自定义事件侦听器来检测此问题?
请问我似乎在任何地方都找不到解决这个问题的方法,我发现这个网站解释了如何创建自定义事件
就像您需要创建事件侦听器一样,您还需要创建事件触发器 - 因为没有自动操作可以为您执行此操作。我提供了示例代码,向您展示了如何实现这样的 firer。
此测试实现并不完美。它仅包括一种添加侦听器的方法。您可能希望包含一种方法来删除不再对接收事件感兴趣的侦听器。另请注意,此类不是线程安全的。
import java.util.List;
import java.util.ArrayList;
import java.util.EventListener;
import java.util.EventObject;
import java.awt.EventQueue;
/**
* This class uses the EventQueue to process its events, but you should only
* really do this if the changes you make have an impact on part of a GUI
* eg. adding a button to a JFrame.
*
* Otherwise, you should create your own event dispatch thread that can handle
* change events
*/
public class BooleanChangeTest implements BooleanChangeDispatcher {
public static void main(String[] args) {
BooleanChangeListener listener = new BooleanChangeListener() {
@Override
public void stateChanged(BooleanChangeEvent event) {
System.out.println("Detected change to: "
+ event.getDispatcher().getFlag()
+ " -- event: " + event);
}
};
BooleanChangeTest test = new BooleanChangeTest(false);
test.addBooleanChangeListener(listener);
test.setFlag(false); // no change, no event dispatch
test.setFlag(true); // changed to true -- event dispatched
}
private boolean flag;
private List<BooleanChangeListener> listeners;
public BooleanChangeTest(boolean initialFlagState) {
flag = initialFlagState;
listeners = new ArrayList<BooleanChangeListener>();
}
@Override
public void addBooleanChangeListener(BooleanChangeListener listener) {
listeners.add(listener);
}
@Override
public void setFlag(boolean flag) {
if (this.flag != flag) {
this.flag = flag;
dispatchEvent();
}
}
@Override
public boolean getFlag() {
return flag;
}
private void dispatchEvent() {
final BooleanChangeEvent event = new BooleanChangeEvent(this);
for (BooleanChangeListener l : listeners) {
dispatchRunnableOnEventQueue(l, event);
}
}
private void dispatchRunnableOnEventQueue(
final BooleanChangeListener listener,
final BooleanChangeEvent event) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
listener.stateChanged(event);
}
});
}
}
interface BooleanChangeDispatcher {
public void addBooleanChangeListener(BooleanChangeListener listener);
public boolean getFlag();
public void setFlag(boolean flag);
}
/**
* Listener interface for classes interested in knowing about a boolean
* flag change.
*/
interface BooleanChangeListener extends EventListener {
public void stateChanged(BooleanChangeEvent event);
}
/**
* This class lets the listener know when the change occured and what
* object was changed.
*/
class BooleanChangeEvent extends EventObject {
private final BooleanChangeDispatcher dispatcher;
public BooleanChangeEvent(BooleanChangeDispatcher dispatcher) {
super(dispatcher);
this.dispatcher = dispatcher;
}
// type safe way to get source (as opposed to getSource of EventObject
public BooleanChangeDispatcher getDispatcher() {
return dispatcher;
}
}
使用属性更改支持。您不必实现那么多,而且它是线程安全的。
public class MyClassWithText {
protected PropertyChangeSupport propertyChangeSupport;
private String text;
public MyClassWithText () {
propertyChangeSupport = new PropertyChangeSupport(this);
}
public void setText(String text) {
String oldText = this.text;
this.text = text;
propertyChangeSupport.firePropertyChange("MyTextProperty",oldText, text);
}
public void addPropertyChangeListener(PropertyChangeListener listener) {
propertyChangeSupport.addPropertyChangeListener(listener);
}
}
public class MyTextListener implements PropertyChangeListener {
@Override
public void propertyChange(PropertyChangeEvent event) {
if (event.getPropertyName().equals("MyTextProperty")) {
System.out.println(event.getNewValue().toString());
}
}
}
public class MyTextTest {
public static void main(String[] args) {
MyClassWithText interestingText = new MyClassWithText();
MyTextListener listener = new MyTextListener();
interestingText.addPropertyChangeListener(listener);
interestingText.setText("FRIST!");
interestingText.setText("it's more like when you take a car, and you...");
}
}