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      1 /*
      2  * Copyright (C) 2015 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 com.android.tv.common;
     18 
     19 import android.os.Handler;
     20 import android.os.Looper;
     21 import android.os.Message;
     22 import android.support.annotation.NonNull;
     23 import java.lang.ref.WeakReference;
     24 
     25 /**
     26  * A Handler that keeps a {@link WeakReference} to an object.
     27  *
     28  * <p>Use this to prevent leaking an Activity or other Context while messages are still pending.
     29  * When you extend this class you <strong>MUST NOT</strong> use a non static inner class, or the
     30  * containing object will still be leaked.
     31  *
     32  * <p>See <a href="http://android-developers.blogspot.com/2009/01/avoiding-memory-leaks.html">
     33  * Avoiding memory leaks</a>.
     34  */
     35 public abstract class WeakHandler<T> extends Handler {
     36     private final WeakReference<T> mRef;
     37 
     38     /**
     39      * Constructs a new handler with a weak reference to the given referent using the provided
     40      * Looper instead of the default one.
     41      *
     42      * @param looper The looper, must not be null.
     43      * @param ref the referent to track
     44      */
     45     public WeakHandler(@NonNull Looper looper, T ref) {
     46         super(looper);
     47         mRef = new WeakReference<>(ref);
     48     }
     49 
     50     /**
     51      * Constructs a new handler with a weak reference to the given referent.
     52      *
     53      * @param ref the referent to track
     54      */
     55     public WeakHandler(T ref) {
     56         mRef = new WeakReference<>(ref);
     57     }
     58 
     59     /** Calls {@link #handleMessage(Message, Object)} if the WeakReference is not cleared. */
     60     @Override
     61     public final void handleMessage(Message msg) {
     62         T referent = mRef.get();
     63         if (referent == null) {
     64             return;
     65         }
     66         handleMessage(msg, referent);
     67     }
     68 
     69     /**
     70      * Subclasses must implement this to receive messages.
     71      *
     72      * <p>If the WeakReference is cleared this method will no longer be called.
     73      *
     74      * @param msg the message to handle
     75      * @param referent the referent. Guaranteed to be non null.
     76      */
     77     protected abstract void handleMessage(Message msg, @NonNull T referent);
     78 }
     79