观察者模式
/** 抽象的主题*/
public abstract class Subject {
ArrayList<Observer> observers=new ArrayList<Observer>();
public abstract void Notify();
public abstract void addObserver(Observer ob);
public abstract void removeObserver(Observer ob);
}
/**
* 观察者抽象接口
* @author pdan
* @da2016年5月11日
*/
public abstract class Observer {
public abstract void Update();
}
/**
* 具体主题;
* @author pdan
* @da2016年5月11日
*/
public class ConcreateSubject extends Subject{
public String status="aaa";
@Override
public void Notify() {
for(Observer ob : observers){
ob.Update();
}
}
@Override
public void addObserver(Observer ob) {
observers.add(ob);
}
@Override
public void removeObserver(Observer ob) {
observers.remove(ob);
}
}
/**
* 具体的观察者
* @author pdan
* @da2016年5月12日
*/
public class ConcreateObserver extends Observer{
ConcreateSubject subject;
public ConcreateObserver(ConcreateSubject subject) {
this.subject=subject;
}
@Override
public void Update() {
System.out.println(subject.status);
}
}
Android中观察这模式的存在: 暂时还没理解...
package AndroidObserver;
/***
* 抽象的观察者。
* @author pdan
* @da2016年5月12日
*/
public abstract class BaseAdapter {
private final DataSetObservable mDataSetObservable = new DataSetObservable();
public void registerDataSetObserver(DataSetObserver observer) {
mDataSetObservable.registerObserver(observer);
}
public void unregisterDataSetObserver(DataSetObserver observer) {
mDataSetObservable.unregisterObserver(observer);
}
/**
* Notifies the attached observers that the underlying data has been changed
* and any View reflecting the data set should refresh itself.
*/
public void notifyDataSetChanged() {
mDataSetObservable.notifyChanged();
}
/**
* Notifies the attached observers that the underlying data is no longer valid
* or available. Once invoked this adapter is no longer valid and should
* not report further data set changes.
*/
public void notifyDataSetInvalidated() {
mDataSetObservable.notifyInvalidated();
}
public boolean areAllItemsEnabled() {
return true;
}
public boolean isEnabled(int position) {
return true;
}
public int getItemViewType(int position) {
return 0;
}
public int getViewTypeCount() {
return 1;
}
/**
* * @return Count of items.
*/
abstract int getCount();
abstract Object getItem(int position);
abstract ListView getView(int position, ListView convertView);
}
package AndroidObserver;
/**抽象的观察者。*/
public abstract class DataSetObserver {
/**
* This method is called when the entire data set has changed,
* most likely through a call to {@link Cursor#requery()} on a {@link Cursor}.
* 当主题发生改变的时候调用此方法
*/
public void onChanged() {
// Do nothing
}
/**
* This method is called when the entire data becomes invalid,
* most likely through a call to {@link Cursor#deactivate()} or {@link Cursor#close()} on a
* {@link Cursor}.
*/
public void onInvalidated() {
// Do nothing
}
}
package AndroidObserver;
import java.util.ArrayList;
/**抽象的观察者*/
public abstract class Observable<T> {
/**
* The list of observers. An observer can be in the list at most
* once and will never be null.
*/
protected final ArrayList<T> mObservers = new ArrayList<T>();
/**
* Adds an observer to the list. The observer cannot be null and it must not already
* be registered.
* @param observer the observer to register
* @throws IllegalArgumentException the observer is null
* @throws IllegalStateException the observer is already registered
*/
public void registerObserver(T observer) {
if (observer == null) {
throw new IllegalArgumentException("The observer is null.");
}
synchronized(mObservers) {
if (mObservers.contains(observer)) {
throw new IllegalStateException("Observer " + observer + " is already registered.");
}
mObservers.add(observer);
}
}
/**
* Removes a previously registered observer. The observer must not be null and it
* must already have been registered.
* @param observer the observer to unregister
* @throws IllegalArgumentException the observer is null
* @throws IllegalStateException the observer is not yet registered
*/
public void unregisterObserver(T observer) {
if (observer == null) {
throw new IllegalArgumentException("The observer is null.");
}
synchronized(mObservers) {
int index = mObservers.indexOf(observer);
if (index == -1) {
throw new IllegalStateException("Observer " + observer + " was not registered.");
}
mObservers.remove(index);
}
}
/**
* Remove all registered observer
*/
public void unregisterAll() {
synchronized(mObservers) {
mObservers.clear();
}
}
}
package AndroidObserver;
/**具体的观察者。*/
public class DataSetObservable extends Observable<DataSetObserver> {
/**
* Invokes onChanged on each observer. Called when the data set being observed has
* changed, and which when read contains the new state of the data.
*/
public void notifyChanged() {
synchronized(mObservers) {
// since onChanged() is implemented by the app, it could do anything, including
// removing itself from {@link mObservers} - and that could cause problems if
// an iterator is used on the ArrayList {@link mObservers}.
// to avoid such problems, just march thru the list in the reverse order.
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onChanged();
}
}
}
/**
* Invokes onInvalidated on each observer. Called when the data set being monitored
* has changed such that it is no longer valid.
*/
public void notifyInvalidated() {
synchronized (mObservers) {
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onInvalidated();
}
}
}
}
package AndroidObserver;
import java.util.ArrayList;
public class ListAdapter extends BaseAdapter{
private ArrayList<String> strs;
public ListAdapter(ArrayList<String> strs) {
this.strs=strs;
}
@Override
int getCount() {
// TODO Auto-generated method stub
return 0;
}
@Override
Object getItem(int position) {
// TODO Auto-generated method stub
return null;
}
@Override
ListView getView(int position, ListView convertView) {
// TODO Auto-generated method stub
return null;
}
}
package AndroidObserver;
public class ListView {
private ListAdapter mAdapter;
private DataSetObserver mDataSetObserver;
public void setAdapter(ListAdapter adapter) {
if (mAdapter != null && mDataSetObserver != null) {
mAdapter.unregisterDataSetObserver(mDataSetObserver);
}
mAdapter = adapter;
}
}
package AndroidObserver;
import java.util.ArrayList;
public class Test {
public static void main(String[] args) {
ArrayList<String> ars = new ArrayList<String>();
ars.add("1");
ars.add("2");
ars.add("3");
ListView listViwe = new ListView();
ListAdapter adapter = new ListAdapter(ars);
listViwe.setAdapter(adapter);
ars.remove(1);
adapter.notifyDataSetChanged();
}
}