79 lines
2.6 KiB
Java
79 lines
2.6 KiB
Java
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/*
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* Copyright (C) 2007 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.database;
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import java.util.ArrayList;
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/**
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* Provides methods for (un)registering arbitrary observers in an ArrayList.
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*/
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public abstract class Observable<T> {
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/**
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* The list of observers. An observer can be in the list at most
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* once and will never be null.
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*/
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protected final ArrayList<T> mObservers = new ArrayList<T>();
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/**
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* Adds an observer to the list. The observer cannot be null and it must not already
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* be registered.
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* @param observer the observer to register
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* @throws IllegalArgumentException the observer is null
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* @throws IllegalStateException the observer is already registered
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*/
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public void registerObserver(T observer) {
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if (observer == null) {
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throw new IllegalArgumentException("The observer is null.");
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}
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synchronized(mObservers) {
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if (mObservers.contains(observer)) {
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throw new IllegalStateException("Observer " + observer + " is already registered.");
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}
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mObservers.add(observer);
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}
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}
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/**
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* Removes a previously registered observer. The observer must not be null and it
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* must already have been registered.
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* @param observer the observer to unregister
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* @throws IllegalArgumentException the observer is null
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* @throws IllegalStateException the observer is not yet registered
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*/
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public void unregisterObserver(T observer) {
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if (observer == null) {
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throw new IllegalArgumentException("The observer is null.");
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}
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synchronized(mObservers) {
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int index = mObservers.indexOf(observer);
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if (index == -1) {
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throw new IllegalStateException("Observer " + observer + " was not registered.");
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}
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mObservers.remove(index);
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}
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}
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/**
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* Remove all registered observer
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*/
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public void unregisterAll() {
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synchronized(mObservers) {
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mObservers.clear();
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}
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}
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}
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