1 files changed, 78 insertions, 0 deletions
diff --git a/core/java/android/database/Observable.java b/core/java/android/database/Observable.java
new file mode 100644
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+++ b/core/java/android/database/Observable.java
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+/*
+ * 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<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();
+        }        
+    }
+}