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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License
     15  */
     16 
     17 package android.location;
     18 
     19 import android.annotation.NonNull;
     20 import android.content.Context;
     21 import android.os.Handler;
     22 import android.os.RemoteException;
     23 import android.util.Log;
     24 
     25 import com.android.internal.util.Preconditions;
     26 
     27 import java.util.ArrayList;
     28 import java.util.Collection;
     29 import java.util.HashMap;
     30 import java.util.Map;
     31 
     32 /**
     33  * A base handler class to manage transport and local listeners.
     34  *
     35  * @hide
     36  */
     37 abstract class LocalListenerHelper<TListener> {
     38     private final HashMap<TListener, Handler> mListeners = new HashMap<>();
     39 
     40     private final String mTag;
     41     private final Context mContext;
     42 
     43     protected LocalListenerHelper(Context context, String name) {
     44         Preconditions.checkNotNull(name);
     45         mContext = context;
     46         mTag = name;
     47     }
     48 
     49     /**
     50      * Adds a {@param listener} to the list of listeners on which callbacks will be executed. The
     51      * execution will happen on the {@param handler} thread or alternatively in the callback thread
     52      * if a  {@code null} handler value is passed.
     53      */
     54     public boolean add(@NonNull TListener listener, Handler handler) {
     55         Preconditions.checkNotNull(listener);
     56         synchronized (mListeners) {
     57             // we need to register with the service first, because we need to find out if the
     58             // service will actually support the request before we attempt anything
     59             if (mListeners.isEmpty()) {
     60                 boolean registeredWithService;
     61                 try {
     62                     registeredWithService = registerWithServer();
     63                 } catch (RemoteException e) {
     64                     Log.e(mTag, "Error handling first listener.", e);
     65                     return false;
     66                 }
     67                 if (!registeredWithService) {
     68                     Log.e(mTag, "Unable to register listener transport.");
     69                     return false;
     70                 }
     71             }
     72             if (mListeners.containsKey(listener)) {
     73                 return true;
     74             }
     75             mListeners.put(listener, handler);
     76             return true;
     77         }
     78     }
     79 
     80     public void remove(@NonNull TListener listener) {
     81         Preconditions.checkNotNull(listener);
     82         synchronized (mListeners) {
     83             boolean removed = mListeners.containsKey(listener);
     84             mListeners.remove(listener);
     85             boolean isLastRemoved = removed && mListeners.isEmpty();
     86             if (isLastRemoved) {
     87                 try {
     88                     unregisterFromServer();
     89                 } catch (RemoteException e) {
     90                     Log.v(mTag, "Error handling last listener removal", e);
     91                 }
     92             }
     93         }
     94     }
     95 
     96     protected abstract boolean registerWithServer() throws RemoteException;
     97     protected abstract void unregisterFromServer() throws RemoteException;
     98 
     99     protected interface ListenerOperation<TListener> {
    100         void execute(TListener listener) throws RemoteException;
    101     }
    102 
    103     protected Context getContext() {
    104         return mContext;
    105     }
    106 
    107     private void executeOperation(ListenerOperation<TListener> operation, TListener listener) {
    108         try {
    109             operation.execute(listener);
    110         } catch (RemoteException e) {
    111             Log.e(mTag, "Error in monitored listener.", e);
    112             // don't return, give a fair chance to all listeners to receive the event
    113         }
    114     }
    115 
    116     protected void foreach(final ListenerOperation<TListener> operation) {
    117         Collection<Map.Entry<TListener, Handler>> listeners;
    118         synchronized (mListeners) {
    119             listeners = new ArrayList<>(mListeners.entrySet());
    120         }
    121         for (final Map.Entry<TListener, Handler> listener : listeners) {
    122             if (listener.getValue() == null) {
    123                 executeOperation(operation, listener.getKey());
    124             } else {
    125                 listener.getValue().post(new Runnable() {
    126                     @Override
    127                     public void run() {
    128                         executeOperation(operation, listener.getKey());
    129                     }
    130                 });
    131             }
    132         }
    133     }
    134 }
    135