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Android example source code file (Observable.java)

This example Android source code file (Observable.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

arraylist, illegalargumentexception, illegalstateexception, observable, observer, the, util

The Observable.java Android example source code

/*
 * 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 (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();

    /**
     * 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();
        }        
    }
}

Other Android examples (source code examples)

Here is a short list of links related to this Android Observable.java source code file:

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