Android设计模式之观察者模式.doc

/* * (Subject)(Observer)* * MVCObserverObserver* SubjectObserver* * * * Observer* * 1. * * 2. * 3. * * 1. Subject* * * 2. Observer* * 3. ConcreteSubject* ConcreteObserver* * 4. ConcreteObserver* ConcreteObserver* * Observer* */UMLAndroid.DataSetObserverObservable<T>DataSetObserverableObserver()DataSetObserver2framework/base/core/java/android/database/DataSetObserver.javapackage android.database;/* Receives call backs when a data set has been changed, or made invalid. The typically data sets* that are observed are link Cursors or link android.widget.Adapters.* DataSetObserver must be implemented by objects which are added to a DataSetObservable.*/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.*/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 nothingSubject()Observable<T>observerframework/base/core/java/android/database/Observable.javapackage android.database;import java.util.ArrayList;/* Provides methods for (un)registering arbitrary observers in an ArrayList.*/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();ConcreateSubject()OberverArrayList<Observer>Oberveractionframework/base/core/java/android/database/DataSetObservable.javapackage android.database;/* A specialization of Observable for DataSetObserver that provides methods for* invoking the various callback methods of DataSetObserver.*/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();ConcreateObserver(),actionandroidframework/base/core/java/android/widget/AbsListView.javaclass AdapterDataSetObserver extends AdapterView<ListAdapter>.AdapterDataSetObserver Overridepublic void onChanged() super.onChanged();if (mFastScroller != null) mFastScroller.onSectionsChanged();Overridepublic void onInvalidated() super.onInvalidated();if (mFastScroller != null) mFastScroller.onSectionsChanged();framework/base/core/java/android/widget/AdapterView.javaclass AdapterDataSetObse()rver extends DataSetObserver private Parcelable mInstanceState = null;Overridepublic void onChanged() mDataChanged = true;mOldItemCount = mItemCount;mItemCount = getAdapter().getCount();if (DBG) Xlog.d(TAG, "AdapterView onChanged: mOldItemCount = " + mOldItemCount+ ",mItemCount = " + mItemCount + ",getAdapter() = " + getAdapter()+ ",AdapterView = " + AdapterView.this, new Throwable("onChanged");/ Detect the case where a cursor that was previously invalidated has/ been repopulated with new data.if (AdapterView.this.getAdapter().hasStableIds() && mInstanceState != null&& mOldItemCount = 0 && mItemCount > 0) AdapterView.this.onRestoreInstanceState(mInstanceState);mInstanceState = null; else rememberSyncState();checkFocus();requestLayout();Overridepublic void onInvalidated() mDataChanged = true;if (DBG) Xlog.d(TAG, "AdapterView onInvalidated: mOldItemCount = " + mOldItemCount+ ",mItemCount = " + mItemCount + ",getAdapter() = " + getAdapter()+ ",AdapterView = " + AdapterView.this, new Throwable("onInvalidated");if (AdapterView.this.getAdapter().hasStableIds() / Remember the current state for the case where our hosting activity is being/ stopped and later restartedmInstanceState = AdapterView.this.onSaveInstanceState();/ Data is invalid so we should reset our statemOldItemCount = mItemCount;mItemCount = 0;mSelectedPosition = INVALID_POSITION;mSelectedRowId = INVALID_ROW_ID;mNextSelectedPosition = INVALID_POSITION;mNextSelectedRowId = INVALID_ROW_ID;mNeedSync = false;checkFocus();requestLayout();public void clearSavedState() mInstanceState = null;BaseAdapterBaseAdapterDataSetObservableregisterDataSetObserverunregisterDataSetObserverObservernotifyDataSetChangedObserveronChange()ListViewBaseAdapterBaseAdapteritemnotifyDataSetChanged()ListviewBaseAdapterregisterDataSetObserver(DataSetObserver observer)ObserverListviewListView/* Sets the data behind this ListView.* The adapter passed to this method may be wrapped by a link WrapperListAdapter,* depending on the ListView features currently in use. For instance, adding* headers and/or footers will cause the adapter to be wrapped.* param adapter The ListAdapter which is responsible for maintaining the* data backing this list and for producing a view to represent an* item in that data set.* see #getAdapter()*/Overridepublic void setAdapter(ListAdapter adapter) if (mAdapter != null && mDataSetObserver != null) mAdapter.unregisterDataSetObserver(mDataSetObserver);resetList();mRecycler.clear();if (mHeaderViewInfos.size() > 0| mFooterViewInfos.size() > 0) mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter); else mAdapter = adapter;mOldSelectedPosition = INVALID_POSITION;mOldSelectedRowId = INVALID_ROW_ID;/ AbsListView#setAdapter will update choice mode states.super.setAdapter(adapter);if (mAdapter != null) mAreAllItemsSelectable = mAdapter.areAllItemsEnabled();mOldItemCount = mItemCount;mItemCount = mAdap