Android Input输入系统之四：KeyEvent事件中的InputChannel通信

快来打我* 2023-06-29 10:36 17阅读 0赞

[《Android按键Input KeyEvent》][Android_Input KeyEvent]  
[《Android Input输入系统之一：KeyEvent事件监听及事件分发流程》][Android Input_KeyEvent]  
[《Android Input输入系统之二：KeyEvent注入事件及事件分发流程》][Android Input_KeyEvent 1]  
[《Android Input输入系统之三：KeyEvent事件分发和上层应用层对事件的接收》][Android Input_KeyEvent 2]  
[《Android Input输入系统之四：KeyEvent事件中的InputChannel通信》][Android Input_KeyEvent_InputChannel]  
[《Android Input输入系统之五：按键调节音量加减》][Android Input]

经过一系列的分析，key事件的分发，中间有一个InputChannel通信。此章节对《Android Input输入系统之三：KeyEvent事件分发和上层应用层对事件的接收》中的socket通信进行一个详细的分析。

key事件发送端，InputDispatcher，属于system\_server进程；  
key事件接收端，ViewRootImpl，是应用程序进程。

这两者之间的跨进程通信就是通过InputChannel实现的。

重点还是看一下InputChannel的创建过程。

/** A window in the window manager. */
    public class WindowState extends WindowContainer<WindowState> implements WindowManagerPolicy.WindowState { 
        void openInputChannel(InputChannel outInputChannel) { 
            if (mInputChannel != null) { 
                throw new IllegalStateException("Window already has an input channel.");
            }
            String name = getName();
            InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
            mInputChannel = inputChannels[0];
            mClientChannel = inputChannels[1];
            mInputWindowHandle.inputChannel = inputChannels[0];
            if (outInputChannel != null) { 
                mClientChannel.transferTo(outInputChannel);
                mClientChannel.dispose();
                mClientChannel = null;
            } else { 
                // If the window died visible, we setup a dummy input channel, so that taps
                // can still detected by input monitor channel, and we can relaunch the app.
                // Create dummy event receiver that simply reports all events as handled.
                mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
            }
            mService.mInputManager.registerInputChannel(mInputChannel, mInputWindowHandle);
        }
    
        @Override
        String getName() { 
            return Integer.toHexString(System.identityHashCode(this))
                    + " " + getWindowTag();
        }
    
        CharSequence getWindowTag() { 
            CharSequence tag = mAttrs.getTitle();
            if (tag == null || tag.length() <= 0) { 
                tag = mAttrs.packageName;
            }
            return tag;
        }
    }

name是window的title名或者包名。

InputChannel\[\] inputChannels = InputChannel.openInputChannelPair(name);

openInputChannelPair()，创建了一对InputChannel分别是mInputChannel和mClientChannel，mInputChannel是服务端的channel,mClientChannel是客户端的channel。

通过mClientChannel.transferTo(outInputChannel);将mClientChannel传递给View应用端的outInputChannel中。即将fd传给客户端。

通过registerInputChannel将mInputChannel注册到InputDispatcher中。  
mService.mInputManager.registerInputChannel(mInputChannel, mInputWindowHandle);

这样就分别创建了一对服务端和客户端的InputChannel，并分别把fd传给服务端和客户端。

建立起了InputDispatcher的View之间的联系。

再理一理View和InputDispatcher之间的联系。

InputDispatcher，事件发送者，system\_server进程；  
View，事件接收者，app进程；

整个流程见下图：  
![从/dev/input/event\*中读取到发送给View的整个流程t][dev_input_event_View_t]

图片来源于以下：

参考资料：  
[https://www.jianshu.com/p/f05d6b05ba17][https_www.jianshu.com_p_f05d6b05ba17]

[Android_Input KeyEvent]: https://blog.csdn.net/Sunxiaolin2016/article/details/103715355
[Android Input_KeyEvent]: https://blog.csdn.net/Sunxiaolin2016/article/details/103716912
[Android Input_KeyEvent 1]: https://blog.csdn.net/Sunxiaolin2016/article/details/103733280
[Android Input_KeyEvent 2]: https://blog.csdn.net/Sunxiaolin2016/article/details/103835884
[Android Input_KeyEvent_InputChannel]: https://blog.csdn.net/Sunxiaolin2016/article/details/103938729
[Android Input]: https://blog.csdn.net/Sunxiaolin2016/article/details/103958303
[dev_input_event_View_t]: https://img-blog.csdnimg.cn/20200113113420771.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1N1bnhpYW9saW4yMDE2,size_16,color_FFFFFF,t_70
[https_www.jianshu.com_p_f05d6b05ba17]: https://www.jianshu.com/p/f05d6b05ba17