相信大家会有这样的需求，一个javabean内有多个变量，每次改变都需要获取到他们的状态，一般我们想到的可能是用接口回调的方法去监听变量的改变，一个javabean还好处理，那如果有很多呢，会使代码显得很臃肿且不好扩展，所以这里有个很好方法来处理以上需求。
在JavaBean的设计中，按照属性的不同作用又细分为四类：单值属性、索引属性、关联属性、限制属性。关联属性，也称之为绑定属性。绑定属性会在属性值发生变化时，通知所有相关的监听器。
先介绍几个api吧
类PropertyChangeSupport
-
addPropertyChangeListener(PropertyChangeListener listener)
顾名思义，添加对bean的监听。 -
removePropertyChangeListener(PropertyChangeListener listener)
移除监听。 -
firePropertyChange(String propertyName, int oldValue, int newValue)
添加对bean内某个变量的监听，第一个参数最好是变量名，第二个是变量改变前的值，第二个是变量改变后的值
类PropertyChangeEvent
https://docs.oracle.com/javase/7/docs/api/java/beans/PropertyChangeEvent.html
- getPropertyName()
获取发生改变的变量名。 - getSource()
获取改变的bean对象 - getOldValue()
获取发生改变的变量的旧值。 - getNewValue()
获取发生改变的变量的新值。
ok，不多说，上代码
javabean类
public class DeviceInfo {
private static DeviceInfo deviceInfo;
public static DeviceInfo getInstance() {
if (deviceInfo == null) {
deviceInfo = new DeviceInfo();
}
return deviceInfo;
}
private PropertyChangeSupport changeSupport = new PropertyChangeSupport(this);
public String getDeviceName() {
return mDeviceName;
}
public void setDeviceName(String deviceName) {
String oldValue = mDeviceName;
this.mDeviceName = deviceName;
changeSupport.firePropertyChange("deviceName", oldValue, deviceName);
}
public String getDeviceStatus() {
return mDeviceStatus;
}
public void setDeviceStatus(String deviceStatus) {
String oldValue = mDeviceStatus;
this.mDeviceStatus = deviceStatus;
changeSupport.firePropertyChange("deviceStatus", oldValue, deviceStatus);
}
private String mDeviceName;
private String mDeviceStatus;
public void addPropertyChangeListener(PropertyChangeListener listener) {
changeSupport.addPropertyChangeListener(listener);
}
public void removePropertyChangeListener(PropertyChangeListener listener) {
changeSupport.removePropertyChangeListener(listener);
}
}
监听类
public class MainActivity extends AppCompatActivity implements PropertyChangeListener{
private static final String TAG = "MainActivity";
private EditText deviceName;
private EditText deviceStatus;
private Button change;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
deviceName = (EditText) findViewById(R.id.et_deviceName);
deviceStatus = (EditText) findViewById(R.id.et_deviceStatus);
change = (Button) findViewById(R.id.bt_change);
change.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String device_name = deviceName.getText().toString().trim();
String device_status = deviceStatus.getText().toString().trim();
DeviceInfo.getInstance().setDeviceName(device_name);
DeviceInfo.getInstance().setDeviceStatus(device_status);
}
});
DeviceInfo.getInstance().addPropertyChangeListener(this);
}
@Override
public void propertyChange(PropertyChangeEvent propertyChangeEvent) {
Log.d(TAG,"Source:"+propertyChangeEvent.getSource());
Log.d(TAG,"PropertyName:"+propertyChangeEvent.getPropertyName());
Log.d(TAG,"OldValue:"+propertyChangeEvent.getOldValue());
Log.d(TAG,"NewValue:"+propertyChangeEvent.getNewValue().toString());
Log.d(TAG,"---------------------------------------------------");
}
}
好的，操作后的打印值：
初次赋值时oldvalue是null，记得判空。
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恩，好啦，特别是当bean很多的时候特别好用，用propertyChangeEvent.getSource()就能区分是哪个bean了。
