BroadcastReceiver学习笔记

BroadcastReceiver 注册过程

BroadcastReceiver 注册的过程大致如下图所示：

           +----------------+      +-------------+       +-------------------------+    +------------------------+
           | ContextWrapper |      | ContextImpl |       | LoadedApk(mPackageInfo) |    | ActivityManagerService |
           +-----+----------+      +------+------+       +------------+------------+    +---------------+--------+
                 |                        |                           |                                 |         
                 |                        |                           |                                 |         
 registerReceiver|                        |                           |                                 |         
                 |                        |                           |                                 |         
 +--------------->                        |                           |                                 |         
                 |        registerReceiver|                           |                                 |         
                 |                        |                           |                                 |         
                 +------------------------>                           |                                 |         
                 |                        |    getReceiverDispatcher  |                                 |         
                 |                        |                           |                                 |         
                 |                        +--------------------------->                                 |         
                 |                        |                           |                                 |         
                 |                        |      [IIntentReceiver]    |                                 |         
                 |                        |                           |                                 |         
                 |                        <---------------------------+                registerReceiver |         
                 |                        |                           |                                 |         
                 |                        +------------------------------------------------------------->         
                 |                        |                           |                                 |         
                 |                        |                           |                                 |         
                 v                        v                           v                                 v         

1. 调用ContextWrapper的registerReceiver方法，然后传入receiver实例和filter实例。

2. 调用ContextImpl的registerReceiverInternal方法， 由LoadedApk类将context、receiver、scheduler（receiver所在进程的handler）等包装成ReceiverDispatcher类。并将其内部类IIntentReceiver返回，传给ActivityManagerService进行注册。

LoadeApk中与BroadcastReceiver注册相关的类结构图如下所示：

                                                                                                              
  +-------------------------------------------------------------+                                                 
  |  LoadedApk                                                  |                                                 
  |                                                             |                                                 
  |     +-------------------+                                   |                                                 
  |     | mReceivers        |        +-----------------------+  |                                                 
  |     +-------------------+        | receiver1->dispatcher |  |                                                 
  |     |  context(Activity)+-------->                       |  |                                                 
  |     |                   |        | receiver2->dispatcher |  |                                                 
  |     |  context          |        |                       |  |                                                 
  |     |                   |        | receiver3->dispatcher |  |                                                 
  |     |  context          |        |                       |  |                                                 
  |     |                   |        |    ...                |  |                                                 
  |     |   ...             |        +-----------------------+  |                                                 
  |     +-------------------+                                   |                                                 
  |                                                             |                                                 
  |                                                             |                                                 
  +-------------------------------------------------------------+                                                 
                                                                                                              

LoadedApk中保存着context与其注册的各个receiver的对应关系，同时也保存着每个receiver与其dispatcher的对应关系。
dispatcher中的IIntentReceiver是与ActivityManagerService沟通的桥梁。其内部结构如下图所示：

+--------------------------------------------------+                                                      
| ReceiverDispatcher                               |                                                      
|   +-------------------------------------------+  |                                                      
|   | InnerReceiver extends IIntentReceiver.Stub|  |                                                      
|   +-------------------------------------------+  |                                                      
|                                                  |                                                      
|   BroadcastReceiver mReceiver;                   |                                                      
|   Context mContext;                              |                                                      
|   Handler mActivityThread;                       |                                                      
|                                                  |                                                      
+--------------------------------------------------+                                                      

ActivityManagerService在其registerReceiver方法中，将传入的IIntentReceiver和filter以及caller保存成如下所示的结构：

+---------------------------------------------------------------------------+                                     
|                                                                           |                                     
|  ActivityManagerService                                                   |                                     
|                                                   +---------------------+ |                                     
|                                                   | ReceiverList        | |                                     
|                                  +-------------+  +---------------------+ |                                     
|                               +-->InnerReceiver+-->    BroadcastFilter1 | |                                     
|      +---------------------+  |  +-------------+  |                     | |                                     
|      | mRegisteredReceivers+--+                   |    BroadcastFilter2 | |                                     
|      +---------------------+  |                   |                     | |                                     
|                               |  +-------------+  |        ...          | |                                     
|                               +-->InnerReceiver|  +---------------------+ |                                     
|                               |  +-------------+                          |                                     
|                               |                                           |                                     
|                               |                                           |                                     
|                               +-->    ...                                 |                                     
|                                                                           |                                     
|                                                                           |                                     
|                             +------------------+                          |                                     
|     +-------------------+   | BroadcastFilter1 |                          |                                     
|     | mReceiverResolver +--->                  |                          |                                     
|     +-------------------+   | BroadcastFilter2 |                          |                                     
|                             |                  |                          |                                     
|                             |     ...          |                          |                                     
|                             +------------------+                          |                                     
|                                                                           |                                     
+---------------------------------------------------------------------------+                                     

保存成这种结构的原因是为后面发送Broadcast提供高效的实现。

Broadcast 发送过程