编写本文的目的是为何第三方软件uc浏览器8.2.2版在我们的设备上安装后是竖屏（portrait）显示的，而不是我们想要的横屏显示（landscape）。我反编译了这个apk里的AndroidManifest.xml，发现和屏幕方向相关的代码：android:screenOrientation="portrait" android:configChanges="orientation|keyboardHidden"在这里设定了默认方向为portrait(竖屏)显示的，而configChanges属性是在设备有gsensor时有反应的，如果没有gsensor就是默认的方向显示。在Activity里有重写了 @Override public void onConfigurationChanged(Configuration newConfig) { super.onConfigurationChanged(newConfig); …...}这样是对屏幕方向改变时做相应的反应。这样做的好处是不会导致Acivity重启，即关闭一个Acitivity又创建一个Activity，会导致onDestroy,onCreate等事件的发生，因而屏幕切换可能会导致与Acitivity状态相关的应用出错。如果你设置了这个选项, 当手机旋转后,当前 Activity 之后调用onConfigurationChanged() 方法. 而不跑 onCreate 方法等. 整体框架如下：
其中在frameworks里又关联了几个重要的类，比如，Configuration.java在frameworks/base/core/java/android/content/res下这里定义了常量： public static final int ORIENTATION_UNDEFINED = 0; public static final int ORIENTATION_PORTRAIT = 1; public static final int ORIENTATION_LANDSCAPE = 2; public static final int ORIENTATION_SQUARE = 3;这些常量就是屏幕方向。这个类实现了Parcelable, Comparable<Configuration>接口。在Parcelable.java接口里有public void writeToParcel(Parcel dest, int flags); * Specific orientation value for a window. * May be any of the same values allowed * for {@link android.content.pm.ActivityInfo#screenOrientation}. * If not set, a default value of * {@link android.content.pm.ActivityInfo#SCREEN_ORIENTATION_UNSPECIFIED} * will be used. */ public int screenOrientation = ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED;看英文注释这是默认的屏幕方向值。然后在这个类的public void writeToParcel(Parcel out, int parcelableFlags) { ….out.writeInt(screenOrientation);//往Parcel读 screenOrientation}public LayoutParams(Parcel in) { …. screenOrientation = in.readInt();//在 Parcel读 screenOrientation}public final int copyFrom(LayoutParams o) { int changes = 0;….. if (screenOrientation != o.screenOrientation) { screenOrientation = o.screenOrientation; changes |= SCREEN_ORIENTATION_CHANGED; return changes; }刚才有发现了 screenOrientation的默认值为ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED。我在追综到 ActivityInfo这个类里，发现；了定义几个屏幕方向的几个常量，这些常量是在AndroidManifest.xml里各个应用主界面activity的屏幕方向的： /** * Options that have been set in the activity declaration in the * manifest: {@link #FLAG_MULTIPROCESS}, * {@link #FLAG_FINISH_ON_TASK_LAUNCH}, {@link #FLAG_CLEAR_TASK_ON_LAUNCH}, * {@link #FLAG_ALWAYS_RETAIN_TASK_STATE}, * {@link #FLAG_STATE_NOT_NEEDED}, {@link #FLAG_EXCLUDE_FROM_RECENTS}, * {@link #FLAG_ALLOW_TASK_REPARENTING}, {@link #FLAG_NO_HISTORY}, * {@link #FLAG_FINISH_ON_CLOSE_SYSTEM_DIALOGS}. */ public int flags; /** * Constant corresponding to <code>unspecified</code> in * the {@link android.R.attr#screenOrientation} attribute. */ public static final int SCREEN_ORIENTATION_UNSPECIFIED = -1; /** * Constant corresponding to <code>landscape</code> in * the {@link android.R.attr#screenOrientation} attribute. */ public static final int SCREEN_ORIENTATION_LANDSCAPE = 0; /** * Constant corresponding to <code>portrait</code> in * the {@link android.R.attr#screenOrientation} attribute. */ public static final int SCREEN_ORIENTATION_PORTRAIT = 1; /** * Constant corresponding to <code>user</code> in * the {@link android.R.attr#screenOrientation} attribute. */ public static final int SCREEN_ORIENTATION_USER = 2; /** * Constant corresponding to <code>behind</code> in * the {@link android.R.attr#screenOrientation} attribute. */ public static final int SCREEN_ORIENTATION_BEHIND = 3; /** * Constant corresponding to <code>sensor</code> in * the {@link android.R.attr#screenOrientation} attribute. */ public static final int SCREEN_ORIENTATION_SENSOR = 4; /** * Constant corresponding to <code>sensor</code> in * the {@link android.R.attr#screenOrientation} attribute. */ public static final int SCREEN_ORIENTATION_NOSENSOR = 5; /** * The preferred screen orientation this activity would like to run in. * From the {@link android.R.attr#screenOrientation} attribute, one of * {@link #SCREEN_ORIENTATION_UNSPECIFIED}, * {@link #SCREEN_ORIENTATION_LANDSCAPE}, * {@link #SCREEN_ORIENTATION_PORTRAIT}, * {@link #SCREEN_ORIENTATION_USER}, * {@link #SCREEN_ORIENTATION_BEHIND}, * {@link #SCREEN_ORIENTATION_SENSOR}, * {@link #SCREEN_ORIENTATION_NOSENSOR}. */ public int screenOrientation = SCREEN_ORIENTATION_UNSPECIFIED;ActivityInfo.java也实现了Parcelable接口，说明也能往里面读和写屏幕方向。在与ActivityInfo.java同目录（frameworks/base/core/java/android/content/pm）下有AcitivityInfo.aidl在这里只封装了parcelable ActivityInfo;。那么现在只有一条线索去追踪屏幕方向切换的实现原理和流程了。那就是WindowManager.java相关的类。我们知道WindowManager.java是给上层调用的服务，所以我发现了IWindowManager.aidl在相同目录下（frameworks/base/core/java/android/view）.系统启动windowManger.java时，它会启动phoneWindowManager.java，该类有一个内部类myOrientationListener扩展自windowOrientationListener.java。windowOrientationListener.java是一个辅助类，当device的方向发生变化时，供windowManger.java调用，用来接收数据。windowOrientationListener.java 内部在sensorManger.java中进行了注册，它回监听G-sensor传来的数据，即x,y,z方向的加速度，收到数据后经过转换处理，若满足Roate条件则调用IwindowManager接口的实现类windowManagerService.java中的setRotation()方法实现转屏。SensorManager通过polling的方式从设备得到Sensor数据, Sensor数据的结构定义在sensor.h里,其中SensorManager只处理了 vector.v, vector.status, time三个域, 分发给已注册的对这些消息的监听者比如第一项 vector.v包含x,y,z三个方向的信息值,就是由 WindowOrientataionLister注册的,当 SensorManager获取到这三个值之后,会传递给 WindowOrientataionLister,后者代码位于:frameworkd/base/core/java/android/view/WindowOrientationListener.javaWindowOrientataionLister接收到这三个值之后,会计算出设备对应的orientation,并且执行 onOrientationChanged函数进一步上传WindowOrientataionLister是个纯虚类,如果在APK里需要控制方向,可以重载一个实例,而Android的系统实例对应在 PhoneWindowManager.java里,名字为MyOrientationListenerframeworks/policies/base/phone/com/android/internal/policy/impl/PhoneWindowManager.java如果需要旋转, MyOrientationListener则会调用以下代码进行窗口旋转:mWindowManager.setRotation(rotation, false, mFancyRotationAnimation); 现在追踪到SensorManager.java在目录frameworks/base/core/java/android/hardware下，同目录下有ISensorservice.aidl，因为在SensorManager.java类里有：public SensorManager(Looper mainLooper) { mSensorService = ISensorService.Stub.asInterface( ServiceManager.getService(Context.SENSOR_SERVICE));…..}在frameworks/base/services/java/com/android/server下有SensorService.java.这个类是通过JNI方法调用HAL层的Sensor.cpp里的方法,对硬件实现初始化和控制。在frameworks/base/core/jni/android_hardware_SensorManager.cpp和frameworks/base/services/jni/com_android_server_SensorService.cpp中都#include <hardware/sensors.h>在这个头文件中我发现#define SENSOR_TYPE_ORIENTATION 3
