Android4.0中判断WIFI P2P选项是否显示的源码分析

     Android 4.0新增WIFI DIRECT的功能，但是在模拟器上以及一些可以升级至4.0的手机或平板，在settings里面仍然没有WIFI DIRECT功能选项。于是出于好奇，所以跟踪了一

     下源码。

   1.  查找在系统设置包中是否有WIFI DIRECT这部分代码处理。

        在Android4.0的源码路径（我的是源码路径为:myandroid_4.0）/packages/apps/Settings/src/com/android/settings/wifi中发现有P2P这个文件夹，哪说明设置包里面具有WIFI DIRECT这部分的代码处理。

    2.   查找在系统设置里对WIFI DIRECT是否有过滤。

          跟踪Settings包源码，终于发现苗头：在WirelessSettings.java (myandroid_4.0\packages\apps\settings\src\com\android\settings) 文件中

    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        ..........................................        ...........................................        WifiP2pManager p2p = (WifiP2pManager) activity.getSystemService(Context.WIFI_P2P_SERVICE);        if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_WIFI_DIRECT)) {            getPreferenceScreen().removePreference(wifiP2p);        } else {            mWifiP2pEnabler = new WifiP2pEnabler(activity, wifiP2p);        }        ...........................................        ...........................................}

    1）分析PackageManager.FEATURE_WIFI_DIRECT：文件PackageManager.java (frameworks\base\core\java\android\content\pm) 中：

          @SdkConstant(SdkConstantType.FEATURE)
           public static final String FEATURE_WIFI_DIRECT = "android.hardware.wifi.direct";//即为传进去做判断的String。

    2）分析getPackageManager()函数

           文件SettingsPreferenceFragment.java (packages\apps\settings\src\com\android\settings)中，

......................................................................    /**     * Returns the PackageManager from the owning Activity.     */    protected PackageManager getPackageManager() {        return getActivity().getPackageManager();    }......................................................................

         分析getAcivity()返回一个Activity。Activity.java (frameworks\base\core\java\android\app) 中没有 getPackageManager()函数；

         由于public class Activity extends ContextThemeWrapper，所以进入文件ContextThemeWrapper.java (frameworks\base\core\java\android\view)中，

         也没有getPackageManager（）函数，同理发现public class ContextThemeWrapper extends ContextWrapper，所以进入文件ContextWrapper.java (frameworks\base\core\java\android\content) ，此时终于见到getPackageManager（）踪影：

         public class ContextWrapper extends Context {
            Context mBase;

            ....................................

            ....................................

             @Override
             public PackageManager getPackageManager() {
                 return mBase.getPackageManager();
              }

            .....................................

           ......................................

           }
          继续跟踪文件Context.java (frameworks\base\core\java\android\content)，发现getPackageManager（）是一个抽象函数：

                   /** Return PackageManager instance to find global package information. */
                   public abstract PackageManager getPackageManager();
          分析到这里其实我也不知到该怎么继续跟踪这个函数了，想想是否跟这个文件（因为class ContextImpl extends Context）有关联ContextImpl.java (frameworks\base\core\java\android\app)，的确找到了关心的代码：

    @Override    public PackageManager getPackageManager() {        if (mPackageManager != null) {            return mPackageManager;        }        IPackageManager pm = ActivityThread.getPackageManager();        if (pm != null) {            // Doesn't matter if we make more than one instance.            return (mPackageManager = new ApplicationPackageManager(this, pm));        }        return null;    }

          因为 final class ApplicationPackageManager extends PackageManager，所以从上面代码分析getPackageManager（）返回一个ApplicationPackageManager.  

       3)  分析getPackageManager().hasSystemFeature（PackageManager.FEATURE_WIFI_DIRECT）

             由上面分析而知，getPackageManager().hasSystemFeature函数应该调到文件ApplicationPackageManager.java (frameworks\base\core\java\android\app) ，

            

final class ApplicationPackageManager extends PackageManager {............................................................    @Override    public boolean hasSystemFeature(String name) {        try {            return mPM.hasSystemFeature(name);        } catch (RemoteException e) {            throw new RuntimeException("Package manager has died", e);        }    }.............................................................}

        mPM.hasSystemFeature(name)经过AIDL实际上调用到文件PackageManagerService.java (frameworks\base\services\java\com\android\server\pm)  

public class PackageManagerService extends IPackageManager.Stub {........................................................................    public boolean hasSystemFeature(String name) {        synchronized (mPackages) {            return mAvailableFeatures.containsKey(name);        }    }......................................................................}

   mAvailableFeatures里面的内容是通过读取/system/etc/permissions下面的文档。具体代码如下所示：

    void readPermissions() {        // Read permissions from .../etc/permission directory.        File libraryDir = new File(Environment.getRootDirectory(), "etc/permissions");        if (!libraryDir.exists() || !libraryDir.isDirectory()) {            Slog.w(TAG, "No directory " + libraryDir + ", skipping");            return;        }        if (!libraryDir.canRead()) {            Slog.w(TAG, "Directory " + libraryDir + " cannot be read");            return;        }        // Iterate over the files in the directory and scan .xml files        for (File f : libraryDir.listFiles()) {            // We'll read platform.xml last            if (f.getPath().endsWith("etc/permissions/platform.xml")) {                continue;            }            if (!f.getPath().endsWith(".xml")) {                Slog.i(TAG, "Non-xml file " + f + " in " + libraryDir + " directory, ignoring");                continue;            }            if (!f.canRead()) {                Slog.w(TAG, "Permissions library file " + f + " cannot be read");                continue;            }            readPermissionsFromXml(f);        }        // Read permissions from .../etc/permissions/platform.xml last so it will take precedence        final File permFile = new File(Environment.getRootDirectory(),                "etc/permissions/platform.xml");        readPermissionsFromXml(permFile);    }    private void readPermissionsFromXml(File permFile) {        FileReader permReader = null;        try {            permReader = new FileReader(permFile);        } catch (FileNotFoundException e) {            Slog.w(TAG, "Couldn't find or open permissions file " + permFile);            return;        }        try {            XmlPullParser parser = Xml.newPullParser();            parser.setInput(permReader);            XmlUtils.beginDocument(parser, "permissions");            while (true) {                XmlUtils.nextElement(parser);                if (parser.getEventType() == XmlPullParser.END_DOCUMENT) {                    break;                }                String name = parser.getName();                if ("group".equals(name)) {                    String gidStr = parser.getAttributeValue(null, "gid");                    if (gidStr != null) {                        int gid = Integer.parseInt(gidStr);                        mGlobalGids = appendInt(mGlobalGids, gid);                    } else {                        Slog.w(TAG, "<group> without gid at "                                + parser.getPositionDescription());                    }                    XmlUtils.skipCurrentTag(parser);                    continue;                } ......................................else if ("feature".equals(name)) {                    String fname = parser.getAttributeValue(null, "name");                    if (fname == null) {                        Slog.w(TAG, "<feature> without name at "                                + parser.getPositionDescription());                    } else {                        //Log.i(TAG, "Got feature " + fname);                        FeatureInfo fi = new FeatureInfo();                        fi.name = fname;                        mAvailableFeatures.put(fname, fi);                    }                    XmlUtils.skipCurrentTag(parser);                    continue;                } else {                    XmlUtils.skipCurrentTag(parser);                    continue;                }            }            permReader.close();        } catch (XmlPullParserException e) {            Slog.w(TAG, "Got execption parsing permissions.", e);        } catch (IOException e) {            Slog.w(TAG, "Got execption parsing permissions.", e);        }    }

3.    验证上面代码分析的正确性。

        1） 启动一个ANDROID 4.0的模拟器，然后通过adb shell进入/system/etc/permissions目录下查看，
                # cd /system/etc/permissions
                # ls
                 com.android.location.provider.xml
                 platform.xml
                #
               的确没有android.hardware.wifi.direct.xml文件。

        2） 因为在源码/frameworks/base/data/etc中有android.hardware.wifi.direct.xml文件，所以我手动拷贝此文件到out/target/product/generic/system/etc/permissions/

               目录下，然后编译源码，然后用命令行指定编译完成的system.img,userdata.img,ramdisk.img来启动模拟器：

               XXX@XXX:~/Android_code/system_img$ /home/XXX/Android_install/android-sdk-linux_x86/tools/emulator  -system system.img -data userdata.img -ramdisk ramdisk.img  -partition-size 256 -avd Android4.0.3-APILevel15

               然后在模拟器设置中看到了WiFi Direct的设置项了，如图所示：

   只是点击时弹出错误框提示“Couldn't start Wi-Fi Direct”,简单的跟踪了一下是WifiP2pService.java中有WifiNative.startP2pSupplicant()的一个判断，跟到JNI层

WifiP2pService.java (frameworks\base\wifi\java\android\net\wifi\p2p)

static jboolean android_net_wifi_startP2pSupplicant(JNIEnv* env, jobject)
{
    return (jboolean)(::wifi_start_p2p_supplicant() == 0); //这个应该是硬件方面的判断。
}
   没有再继续跟踪下去了，至少关于WIFI P2P设置的过滤过程已经清楚了。