Android framework源码按键操作的完整流程

我们知道按键是底层通过input系统传值上来的，这里面相关的服务是InputManagerService.java,对应的代码路径在frameworks\base\services\java\com\android\server\input\inputManagerService.java
在frameworks\base\services\java\com\android\server目录下有很多Android源生的服务，大家有兴趣的可以去研究。

这里面提到的inputManagerService又是在哪里被启动的呢，Android系统被启动的过程中创建的第一个进程zygote，在他的fork函数里面会创建SystemServer对象，我们可以看看SystemServer这个类又做了哪些事情。SystemServer的路径在frameworks/base/services/java/com/android/server/SystemServer.java
他的main函数如下：

public static void main(String[] args) {

        /*
         * In case the runtime switched since last boot (such as when
         * the old runtime was removed in an OTA), set the system
         * property so that it is in sync. We can't do this in
         * libnativehelper's JniInvocation::Init code where we already
         * had to fallback to a different runtime because it is
         * running as root and we need to be the system user to set
         * the property. http://b/11463182
         */
        SystemProperties.set("persist.sys.dalvik.vm.lib",
                             VMRuntime.getRuntime().vmLibrary());

        if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
            // If a device's clock is before 1970 (before 0), a lot of
            // APIs crash dealing with negative numbers, notably
            // java.io.File#setLastModified, so instead we fake it and
            // hope that time from cell towers or NTP fixes it
            // shortly.
            Slog.w(TAG, "System clock is before 1970; setting to 1970.");
            SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
        }

        if (SamplingProfilerIntegration.isEnabled()) {
            SamplingProfilerIntegration.start();
            timer = new Timer();
            timer.schedule(new TimerTask() {
                @Override
                public void run() {
                    SamplingProfilerIntegration.writeSnapshot("system_server", null);
                }
            }, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);
        }

        // Mmmmmm... more memory!
        dalvik.system.VMRuntime.getRuntime().clearGrowthLimit();

        // The system server has to run all of the time, so it needs to be
        // as efficient as possible with its memory usage.
        VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);

        Environment.setUserRequired(true);

        System.loadLibrary("android_servers");

        Slog.i(TAG, "Entered the Android system server!");

        // Initialize native services.
        nativeInit();

        // This used to be its own separate thread, but now it is
        // just the loop we run on the main thread.
        ServerThread thr = new ServerThread();
        thr.initAndLoop();
    }

这里面有个线程是执行initAndLoop方法，我们打开这个方法就会发现inputManagerService对象被new出来了。相关代码如下：

           Slog.i(TAG, "Input Manager");
            inputManager = new InputManagerService(context, wmHandler);

            Slog.i(TAG, "Window Manager");
            wm = WindowManagerService.main(context, power, display, inputManager,
                    wmHandler, factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL,
                    !firstBoot, onlyCore);
            ServiceManager.addService(Context.WINDOW_SERVICE, wm);
            ServiceManager.addService(Context.INPUT_SERVICE, inputManager);

            ActivityManagerService.self().setWindowManager(wm);

            inputManager.setWindowManagerCallbacks(wm.getInputMonitor());
            inputManager.start();

            display.setWindowManager(wm);
            display.setInputManager(inputManager);