按键驱动调试总结
今天把6516的按键调试结束总结一下；
本身mtk6516的工程已经整合的很好，客户在修改上很方便，有个专门的工具来修改按键，通过对pcb上的按键进行row colum的定位就知道你需要
修改的按键在什么地方了， 当然这个要根据情况来修改， 说实话，真的太简单了。。
调试后分析了一下，按键的整个调试和驱动的流程。
\alps\frameworks\base\libs\ui\EventHub.cpp 这个文件就用户输入系统的中枢。 我分析了一下这个文件。
一、Android底层按键事件处理过程
在系统启动后，在文件。。。中，android 会通过
static const char *device_path = "/dev/input";
bool EventHub::penPlatformInput(void)
res = scan_dir(device_path);
bool EventHub::penPlatformInput(void)
res = scan_dir(device_path);
通过下面的函数打开设备。
//从目录下查找设备
看到这个一段程序
//从目录下查找设备
int EventHub::scan_dir(const char *dirname)
{
char devname[PATH_MAX];
char *filename;
DIR *dir;
struct dirent *de;
dir = opendir(dirname);
if(dir == NULL)
return -1;
strcpy(devname, dirname);
filename = devname + strlen(devname);
*filename++ = '/';
while((de = readdir(dir))) {
if(de->d_name[0] == '.' &&
(de->d_name[1] == '\0' ||
(de->d_name[1] == '.' && de->d_name[2] == '\0')))
continue;
strcpy(filename, de->d_name);
open_device(devname);
}
closedir(dir);
return 0;
}找到后就调用 int EventHub::open_device(const char *deviceName) 打开设备。 static const char *device_path = "/dev/input"; 这个目录下的都是被搜索到。 int EventHub::open_device(const char *deviceName)
{
int version;
int fd;
struct pollfd *new_mFDs;
device_t **new_devices;
char **new_device_names;
char name[80];
char location[80];
char idstr[80];
struct input_id id;
LOGV("Opening device: %s", deviceName);
AutoMutex _l(mLock);
fd = open(deviceName, O_RDWR);
if(fd < 0) {
LOGE("could not open %s, %s\n", deviceName, strerror(errno));
return -1;
}
if(ioctl(fd, EVIOCGVERSION, &version)) {
LOGE("could not get driver version for %s, %s\n", deviceName, strerror(errno));
return -1;
}
if(ioctl(fd, EVIOCGID, &id)) {
LOGE("could not get driver id for %s, %s\n", deviceName, strerror(errno));
return -1;
}
name[sizeof(name) - 1] = '\0';
location[sizeof(location) - 1] = '\0';
idstr[sizeof(idstr) - 1] = '\0';
if(ioctl(fd, EVIOCGNAME(sizeof(name) - 1), &name) < 1) {
//fprintf(stderr, "could not get device name for %s, %s\n", deviceName, strerror(errno));
name[0] = '\0';
}
// check to see if the device is on our excluded list
List<String8>::iterator iter = mExcludedDevices.begin();
List<String8>::iterator end = mExcludedDevices.end();
for ( ; iter != end; iter++) {
const char* test = *iter;
if (strcmp(name, test) == 0) {
LOGI("ignoring event id %s driver %s\n", deviceName, test);
close(fd);
fd = -1;
return -1;
}
}
if(ioctl(fd, EVIOCGPHYS(sizeof(location) - 1), &location) < 1) {
//fprintf(stderr, "could not get location for %s, %s\n", deviceName, strerror(errno));
location[0] = '\0';
}
if(ioctl(fd, EVIOCGUNIQ(sizeof(idstr) - 1), &idstr) < 1) {
//fprintf(stderr, "could not get idstring for %s, %s\n", deviceName, strerror(errno));
idstr[0] = '\0';
}
int devid = 0;
while (devid < mNumDevicesById) {
if (mDevicesById[devid].device == NULL) {
break;
}
devid++;
}
if (devid >= mNumDevicesById) {
device_ent* new_devids = (device_ent*)realloc(mDevicesById,
sizeof(mDevicesById[0]) * (devid + 1));
if (new_devids == NULL) {
LOGE("out of memory");
return -1;
}
mDevicesById = new_devids;
mNumDevicesById = devid+1;
mDevicesById[devid].device = NULL;
mDevicesById[devid].seq = 0;
}
mDevicesById[devid].seq = (mDevicesById[devid].seq+(1<<SEQ_SHIFT))&SEQ_MASK;
if (mDevicesById[devid].seq == 0) {
mDevicesById[devid].seq = 1<<SEQ_SHIFT;
}
new_mFDs = (pollfd*)realloc(mFDs, sizeof(mFDs[0]) * (mFDCount + 1));
new_devices = (device_t**)realloc(mDevices, sizeof(mDevices[0]) * (mFDCount + 1));
if (new_mFDs == NULL || new_devices == NULL) {
LOGE("out of memory");
return -1;
}
mFDs = new_mFDs;
mDevices = new_devices;
#if 0
LOGI("add device %d: %s\n", mFDCount, deviceName);
LOGI(" bus: %04x\n"
" vendor %04x\n"
" product %04x\n"
" version %04x\n",
id.bustype, id.vendor, id.product, id.version);
LOGI(" name: \"%s\"\n", name);
LOGI(" location: \"%s\"\n"
" id: \"%s\"\n", location, idstr);
LOGI(" version: %d.%d.%d\n",
version >> 16, (version >> 8) & 0xff, version & 0xff);
#endif
device_t* device = new device_t(devid|mDevicesById[devid].seq, deviceName, name);
if (device == NULL) {
LOGE("out of memory");
return -1;
}
mFDs[mFDCount].fd = fd;
mFDs[mFDCount].events = POLLIN;
// figure out the kinds of events the device reports
// See if this is a keyboard, and classify it. Note that we only
// consider up through the function keys; we don't want to include
// ones after that (play cd etc) so we don't mistakenly consider a
// controller to be a keyboard.
uint8_t key_bitmask[(KEY_MAX+7)/8];
memset(key_bitmask, 0, sizeof(key_bitmask));
LOGV("Getting keys...");
if (ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(key_bitmask)), key_bitmask) >= 0) {
//LOGI("MAP\n");
//for (int i=0; i<((KEY_MAX+7)/8); i++) {
// LOGI("%d: 0x%02x\n", i, key_bitmask[i]);
//}
for (int i=0; i<((BTN_MISC+7)/8); i++) {
if (key_bitmask[i] != 0) {
device->classes |= CLASS_KEYBOARD;
break;
}
}
if ((device->classes & CLASS_KEYBOARD) != 0) {
device->keyBitmask = new uint8_t[sizeof(key_bitmask)];
if (device->keyBitmask != NULL) {
memcpy(device->keyBitmask, key_bitmask, sizeof(key_bitmask));
} else {
delete device;
LOGE("out of memory allocating key bitmask");
return -1;
}
}
}
// See if this is a trackball.
if (test_bit(BTN_MOUSE, key_bitmask)) {
uint8_t rel_bitmask[(REL_MAX+7)/8];
memset(rel_bitmask, 0, sizeof(rel_bitmask));
LOGV("Getting relative controllers...");
if (ioctl(fd, EVIOCGBIT(EV_REL, sizeof(rel_bitmask)), rel_bitmask) >= 0)
{
if (test_bit(REL_X, rel_bitmask) && test_bit(REL_Y, rel_bitmask)) {
device->classes |= CLASS_TRACKBALL;
}
}
}
uint8_t abs_bitmask[(ABS_MAX+7)/8];
memset(abs_bitmask, 0, sizeof(abs_bitmask));
LOGV("Getting absolute controllers...");
ioctl(fd, EVIOCGBIT(EV_ABS, sizeof(abs_bitmask)), abs_bitmask);
// Is this a new modern multi-touch driver?
if (test_bit(ABS_MT_TOUCH_MAJOR, abs_bitmask)
&& test_bit(ABS_MT_POSITION_X, abs_bitmask)
&& test_bit(ABS_MT_POSITION_Y, abs_bitmask)) {
device->classes |= CLASS_TOUCHSCREEN | CLASS_TOUCHSCREEN_MT;
// Is this an old style single-touch driver?
} else if (test_bit(BTN_TOUCH, key_bitmask)
&& test_bit(ABS_X, abs_bitmask) && test_bit(ABS_Y, abs_bitmask)) {
device->classes |= CLASS_TOUCHSCREEN;
}
#ifdef EV_SW
// figure out the switches this device reports
uint8_t sw_bitmask[(SW_MAX+7)/8];
memset(sw_bitmask, 0, sizeof(sw_bitmask));
if (ioctl(fd, EVIOCGBIT(EV_SW, sizeof(sw_bitmask)), sw_bitmask) >= 0) {
for (int i=0; i<EV_SW; i++) {
//LOGI("Device 0x%x sw %d: has=%d", device->id, i, test_bit(i, sw_bitmask));
if (test_bit(i, sw_bitmask)) {
if (mSwitches[i] == 0) {
mSwitches[i] = device->id;
}
}
}
}
#endif
if ((device->classes&CLASS_KEYBOARD) != 0) {
char tmpfn[sizeof(name)];
char keylayoutFilename[300];
// a more descriptive name
device->name = name;
// replace all the spaces with underscores
strcpy(tmpfn, name);
for (char *p = strchr(tmpfn, ' '); p && *p; p = strchr(tmpfn, ' '))
*p = '_';
// find the .kl file we need for this device
const char* root = getenv("ANDROID_ROOT");//取得root权限
snprintf(keylayoutFilename, sizeof(keylayoutFilename),
"%s/usr/keylayout/%s.kl", root, tmpfn);
bool defaultKeymap = false;
if (access(keylayoutFilename, R_OK)) {
snprintf(keylayoutFilename, sizeof(keylayoutFilename),//不能调用特定的kl文件就要用默认的。
"%s/usr/keylayout/%s", root, "qwerty.kl");
defaultKeymap = true;
}
device->layoutMap->load(keylayoutFilename);//交给keylayoutmap 解析，这个是一个内部类
// tell the world about the devname (the descriptive name)
if (!mHaveFirstKeyboard && !defaultKeymap && strstr(name, "-keypad")) {
// the built-in keyboard has a well-known device ID of 0,
// this device better not go away.
mHaveFirstKeyboard = true;
mFirstKeyboardId = device->id;
property_set("hw.keyboards.0.devname", name);
} else {
// ensure mFirstKeyboardId is set to -something-.
if (mFirstKeyboardId == 0) {
mFirstKeyboardId = device->id;
}
}
char propName[100];
sprintf(propName, "hw.keyboards.%u.devname", device->id);
property_set(propName, name);
// 'Q' key support = cheap test of whether this is an alpha-capable kbd
if (hasKeycode(device, kKeyCodeQ)) {
device->classes |= CLASS_ALPHAKEY;
}
// See if this has a DPAD.
if (hasKeycode(device, kKeyCodeDpadUp) &&
hasKeycode(device, kKeyCodeDpadDown) &&
hasKeycode(device, kKeyCodeDpadLeft) &&
hasKeycode(device, kKeyCodeDpadRight) &&
hasKeycode(device, kKeyCodeDpadCenter)) {
device->classes |= CLASS_DPAD;
}
LOGI("New keyboard: device->id=0x%x devname='%s' propName='%s' keylayout='%s'\n",
device->id, name, propName, keylayoutFilename);
}
LOGI("New device: path=%s name=%s id=0x%x (of 0x%x) index=%d fd=%d classes=0x%x\n",
deviceName, name, device->id, mNumDevicesById, mFDCount, fd, device->classes);
LOGV("Adding device %s %p at %d, id = %d, classes = 0x%x\n",
deviceName, device, mFDCount, devid, device->classes);
mDevicesById[devid].device = device;
device->next = mOpeningDevices;
mOpeningDevices = device;
mDevices[mFDCount] = device;
mFDCount++;
return 0;
}
看到这个一段程序
// find the .kl file we need for this device
const char* root = getenv("ANDROID_ROOT");//取得root权限
snprintf(keylayoutFilename, sizeof(keylayoutFilename),
"%s/usr/keylayout/%s.kl", root, tmpfn);
bool defaultKeymap = false;
if (access(keylayoutFilename, R_OK)) {
snprintf(keylayoutFilename, sizeof(keylayoutFilename),//不能调用特定的kl文件就要用默认的。
"%s/usr/keylayout/%s", root, "qwerty.kl");
defaultKeymap = true;
}
device->layoutMap->load(keylayoutFilename);//交给keylayoutmap 解析，这个是一个内部类
还有一个消息获取函数//获取事件，无限循环得到事件，调用阻塞函数等待
bool EventHub::getEvent(int32_t* outDeviceId, int32_t* outType,
int32_t* outScancode, int32_t* outKeycode, uint32_t *outFlags,
int32_t* outValue, nsecs_t* outWhen)
{
*outDeviceId = 0;
*outType = 0;
*outScancode = 0;
*outKeycode = 0;
*outFlags = 0;
*outValue = 0;
*outWhen = 0;
status_t err;
fd_set readfds;
int maxFd = -1;
int cc;
int i;
int res;
int pollres;
struct input_event iev;
// Note that we only allow one caller to getEvent(), so don't need
// to do locking here... only when adding/removing devices.
if (!mOpened) {
mError = openPlatformInput() ? NO_ERROR : UNKNOWN_ERROR;
mOpened = true;
}
while(1) {
// First, report any devices that had last been added/removed.
if (mClosingDevices != NULL) {
device_t* device = mClosingDevices;
LOGV("Reporting device closed: id=0x%x, name=%s\n",
device->id, device->path.string());
mClosingDevices = device->next;
*outDeviceId = device->id;
if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0;
*outType = DEVICE_REMOVED;
delete device;
return true;
}
if (mOpeningDevices != NULL) {
device_t* device = mOpeningDevices;
LOGV("Reporting device opened: id=0x%x, name=%s\n",
device->id, device->path.string());
mOpeningDevices = device->next;
*outDeviceId = device->id;
if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0;
*outType = DEVICE_ADDED;
return true;
}
release_wake_lock(WAKE_LOCK_ID);
// 阻塞等待！！！！！
pollres = poll(mFDs, mFDCount, -1);
acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);
if (pollres <= 0) {
if (errno != EINTR) {
LOGW("select failed (errno=%d)\n", errno);
usleep(100000);
}
continue;
}
//printf("poll %d, returned %d\n", mFDCount, pollres);
// mFDs[0] is used for inotify, so process regular events starting at mFDs[1]
for(i = 1; i < mFDCount; i++) {
if(mFDs[i].revents) {
LOGV("revents for %d = 0x%08x", i, mFDs[i].revents);
if(mFDs[i].revents & POLLIN) {
res = read(mFDs[i].fd, &iev, sizeof(iev));//读取信息！！事件代码
if (res == sizeof(iev)) {
LOGV("%s got: t0=%d, t1=%d, type=%d, code=%d, v=%d",
mDevices[i]->path.string(),
(int) iev.time.tv_sec, (int) iev.time.tv_usec,
iev.type, iev.code, iev.value);
*outDeviceId = mDevices[i]->id;
if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0;
*outType = iev.type;
*outScancode = iev.code;
if (iev.type == EV_KEY) {
err = mDevices[i]->layoutMap->map(iev.code, outKeycode, outFlags);
LOGV("iev.code=%d outKeycode=%d outFlags=0x%08x err=%d\n",
iev.code, *outKeycode, *outFlags, err);
if (err != 0) {
*outKeycode = 0;
*outFlags = 0;
}
#ifdef HAVE_AEE_FEATURE
#ifdef AEE_MANUAL_DB_DUMP
aee_aed_dump_db((unsigned int)iev.code,
(signed int)iev.value, 0);
#endif
#endif
} else {
*outKeycode = iev.code;
}
*outValue = iev.value;
*outWhen = s2ns(iev.time.tv_sec) + us2ns(iev.time.tv_usec);
return true;
} else {
if (res<0) {
LOGW("could not get event (errno=%d)", errno);
} else {
LOGE("could not get event (wrong size: %d)", res);
}
continue;
}
}
}
}
// read_notify() will modify mFDs and mFDCount, so this must be done after
// processing all other events.
if(mFDs[0].revents & POLLIN) {
read_notify(mFDs[0].fd);
}
}
} 打开设备的时候，如果 device->classes&CLASS_KEYBOARD 不等于 0 表明是键盘。
常用输入设备的定义有：
enum {
CLASS_KEYBOARD = 0x00000001, //键盘
CLASS_ALPHAKEY = 0x00000002, //
CLASS_TOUCHSCREEN = 0x00000004, //触摸屏
CLASS_TRACKBALL = 0x00000008 //轨迹球
};
常用输入设备的定义有：
enum {
CLASS_KEYBOARD = 0x00000001, //键盘
CLASS_ALPHAKEY = 0x00000002, //
CLASS_TOUCHSCREEN = 0x00000004, //触摸屏
CLASS_TRACKBALL = 0x00000008 //轨迹球
};
打开键盘设备的时候通过上面的 ioctl 获得设备名称，命令字 EVIOCGNAME 的定义在文件：
kernel/include/linux/input.h 中。
对于按键事件，调用mDevices->layoutMap->map进行映射，调用的是文件 KeyLayoutMap.cpp
对于按键事件，调用mDevices->layoutMap->map进行映射，调用的是文件 KeyLayoutMap.cpp
(frameworks\base\libs\ui)中的函数：
status_t KeyLayoutMap::load(const char* filename)通过解析 <Driver name>.kl 把按键的
status_t KeyLayoutMap::load(const char* filename)通过解析 <Driver name>.kl 把按键的
映射关系保存在 ：KeyedVector<int32_t,Key> m_keys; 中。
当获得按键事件以后调用： status_t KeyLayoutMap::map(int32_t scancode, int32_t
*keycode, uint32_t *flags)
由映射关系 KeyedVector<int32_t,Key> m_keys 把扫描码转换成andorid上层可以识别的按键。
由映射关系 KeyedVector<int32_t,Key> m_keys 把扫描码转换成andorid上层可以识别的按键。
二、按键映射
Key layout maps的路径是 /system/usr/keylayout，第一个查找的名字是按键驱动的名字，例如
mxckpd.kl。如果没有的话，默认为qwerty.kl。
Key character maps的路径是 /system/usr/keychars，第一个查找的名字是按键驱动的名字，例如
Key character maps的路径是 /system/usr/keychars，第一个查找的名字是按键驱动的名字，例如
mxckpd.kcm。如果没有的话，默认为qwerty.kl。
qwerty.kl是 UTF-8类型的，格式为：key SCANCODE KEYCODE [FLAGS...]。
SCANCODE表示按键扫描码；
KEYCODE表示键值，例如HOME,BACK,1,2,3...
FLAGS有如下定义：
SHIFT: While pressed, the shift key modifier is set
ALT: While pressed, the alt key modifier is set
CAPS: While pressed, the caps lock key modifier is set
WAKE: When this key is pressed while the device is asleep, the device will
qwerty.kl是 UTF-8类型的，格式为：key SCANCODE KEYCODE [FLAGS...]。
SCANCODE表示按键扫描码；
KEYCODE表示键值，例如HOME,BACK,1,2,3...
FLAGS有如下定义：
SHIFT: While pressed, the shift key modifier is set
ALT: While pressed, the alt key modifier is set
CAPS: While pressed, the caps lock key modifier is set
WAKE: When this key is pressed while the device is asleep, the device will
wake up and the key event gets sent to the app.
WAKE_DROPPED: When this key is pressed while the device is asleep, the device
WAKE_DROPPED: When this key is pressed while the device is asleep, the device
will wake up and the key event does not get sent to the app
qwerty.kcm文件为了节省空间，在编译过程中会用工具makekcharmap转化为二进制文件qwerty.bin。
qwerty.kcm文件为了节省空间，在编译过程中会用工具makekcharmap转化为二进制文件qwerty.bin。
三、按键分发
1、输入事件分发线程
在frameworks/base/services/java/com/android/server/WindowManagerService.java里创
在frameworks/base/services/java/com/android/server/WindowManagerService.java里创
建了一个输入事件分发线程，它负责把事件分发到相应的窗口上去。
在WindowManagerService类的构造函数WindowManagerService()中：
mQueue = new KeyQ(); //读取按键
mInputThread = new InputDispatcherThread(); //创建分发线程
...
mInputThread.start();
在启动的线程InputDispatcherThread中：
run()
process();
QueuedEvent ev = mQueue.getEvent(...)
在process() 方法中进行处理事件：
switch (ev.classType)
case RawInputEvent.CLASS_KEYBOARD:
...
dispatchKey((KeyEvent)ev.event, 0, 0);
mQueue.recycleEvent(ev);
break;
case RawInputEvent.CLASS_TOUCHSCREEN:
//Log.i(TAG, "Read next event " + ev);
dispatchPointer(ev, (MotionEvent)ev.event, 0, 0);
break;
case RawInputEvent.CLASS_TRACKBALL:
dispatchTrackball(ev, (MotionEvent)ev.event, 0, 0);
break;
2、上层读取按键的流程
在WindowManagerService类的构造函数WindowManagerService()中：
mQueue = new KeyQ(); //读取按键
mInputThread = new InputDispatcherThread(); //创建分发线程
...
mInputThread.start();
在启动的线程InputDispatcherThread中：
run()
process();
QueuedEvent ev = mQueue.getEvent(...)
在process() 方法中进行处理事件：
switch (ev.classType)
case RawInputEvent.CLASS_KEYBOARD:
...
dispatchKey((KeyEvent)ev.event, 0, 0);
mQueue.recycleEvent(ev);
break;
case RawInputEvent.CLASS_TOUCHSCREEN:
//Log.i(TAG, "Read next event " + ev);
dispatchPointer(ev, (MotionEvent)ev.event, 0, 0);
break;
case RawInputEvent.CLASS_TRACKBALL:
dispatchTrackball(ev, (MotionEvent)ev.event, 0, 0);
break;
2、上层读取按键的流程
WindowManagerService() //(frameworks\base\services\java\com\android\server
\WindowManagerService.java)
|
KeyQ() //KeyQ 是抽象类 KeyInputQueue 的实现
|
InputDeviceReader //在 KeyInputQueue 类中创建的线程
|
readEvent() //
|
android_server_KeyInputQueue_readEvent() //frameworks\base\services\jni\
|
KeyQ() //KeyQ 是抽象类 KeyInputQueue 的实现
|
InputDeviceReader //在 KeyInputQueue 类中创建的线程
|
readEvent() //
|
android_server_KeyInputQueue_readEvent() //frameworks\base\services\jni\
com_android_server_KeyInputQueue.cpp
|
hub->getEvent()
|
EventHub::getEvent() //frameworks\base\libs\ui\EventHub.cpp
|
res = read(mFDs.fd, &iev, sizeof(iev)); //
|
hub->getEvent()
|
EventHub::getEvent() //frameworks\base\libs\ui\EventHub.cpp
|
res = read(mFDs.fd, &iev, sizeof(iev)); //
摘取网上的一段资料
键盘消息是window manager从驱动里面获取的，然后分发给应用程序框架的
具体参考如下：
2.1 第一步:用户数据收集及其初步判定
KeyInputQ在WindowMangerService中建立一个独立的线程InputDeviceReader，使用Native函数readEvent来读取Linux Driver的数据构建RawEvent，放入到KeyQ消息队列中。
preProcessEvent()@KeyInptQ@KeyInputQueue.java这个是在输入系统中的第一个拦截函数原型。KeyQ重载了preProcessEvent()@WindowManagerService.java。在该成员函数中进行如下动作：
（1） 根据PowerManager获取的Screen on,Screen off状态来判定用户输入的是否WakeUPScreen。
（2） 如果按键式应用程序切换按键，则切换应用程序。
（3） 根据WindowManagerPolicy觉得该用户输入是否投递。
2.2 第二步 消息分发第一层面
InputDispatcherThread从KeyQ中读取Events，找到Window Manager中的Focus Window，通过Focus Window记录的mClient接口，将Events专递到Client端。
如何将KeyEvent对象传到Client端：
在前面的章节（窗口管理ViewRoot，Window Manager Proxy）我们已经知道：在客户端建立Window Manager Proxy后，添加窗口到Window Manager service时，带了一个跟客户ViewRoot相关的IWindow接口实例过去，记录在WindowState中的mClient成员变量中。通过IWindow这个AIDL接口实例，Service可以访问客户端的信息，IWindow是Service连接View桥梁。
看看在Client ViewRootKeyEvent的分发过程
IWindow：dispatchKey(event)
dispatchKey(event)@W@ViewRoot@ViewRoot.java
ViewRoot.dispatchKey(event)@ViewRoot.java
message>
sendMessageAtTime(msg)@Handler@Handler.java
至此我们通过前面的Looper，Handler详解章节的分析结论，我们可以知道Key Message已经放入到应用程序的消息队列。
2.3第三步：应用消息队列分发
消息的分发,在Looper，Handler详解章节我们分析了Looper.loop()在最后后面调用了handleMesage.
…
ActivityThread.main()
Looper.loop()
ViewRoot$RootHandler().dispatch()
handleMessage
....
注意到在分发的调用msg.target.dispatch()，而这个target在第二层将消息sendMessageAtTime到消息队列时填入了mag.target=this即为msg.target=ViewRoot实例。所有此时handleMessage就是ViewRoot重载的handleMessage函数。
handlerMessage@ViewRoot@ViewRoot.java
deliverkeyEvent
如果输入法存在，dispatchKey到输入法服务。
否则deliverKeyEventToViewHierarchy@ViewRoot.java
在这里需要强调的是，输入法的KeyEvent的拦截并没有放入到Window Manager Service中，而是放入到了客户端的RootView中来处理。
2.4第四步：向焦点进发，完成焦点路径的遍历。
分发函数调用栈
deliverKeyEventToViewHierarchy@ViewRoot.java
mView.dispatchKeyEvent：mView是与ViewRoot相对应的Top-Level View.如果mView是一个ViewGroup则分发消息到他的mFocus。
mView.dispatchKeyEvent @ViewGroup （ViewRoot@root）
Event.dispatch
mFocus.dispatchKeyEevnet
如果此时的mFocu还是一个ViewGroup，这回将事件专递到下一层的焦点，直到mFocus为一个View。通过这轮调用，就遍历了焦点Path，至此，用户事件传递完成一个段落。
2.5第五步 缺省处理
如果事件在上述Focus View没有处理掉，并且为方向键之类的焦点转换相关按键，则转移焦点到下一个View。
