Android源码学习(一) 数据集观察者
查看Android源码发现这个,决定记下下来。
1.在android.database这个包下面,存在这样一个抽象类DataSetObserver,里面包括onChanged()和onInvalidated()这个两个方法,用来监听数据的改变,在方法内要执行的操作。
/* * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.database; /** * Receives call backs when a data set has been changed, or made invalid. The typically data sets * that are observed are {@link Cursor}s or {@link android.widget.Adapter}s. * 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 nothing } }
2.同级目录中存在Observable这样一个类,如果将上面的DataSetObserver作为这个类的泛型参数。
/* * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.database; import java.util.ArrayList; /** * Provides methods for registering or unregistering arbitrary observers in an {@link ArrayList}. * * This abstract class is intended to be subclassed and specialized to maintain * a registry of observers of specific types and dispatch notifications to them. * * @param T The observer type. */ 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); ) { throw new IllegalStateException("Observer " + observer + " was not registered."); } mObservers.remove(index); } } /** * Remove all registered observers. */ public void unregisterAll() { synchronized(mObservers) { mObservers.clear(); } } }
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