About Android Device Manager-devicepolicymanager (i)

    There is a Device Manager option in security settings, Andorid, and I believe most Android users are less likely to pay attention to this stuff. Recently, after installing an application, I found the contents of this thing changed. What's going on, research and research look. </span>

Old ideas, from the most obvious clues to start analysis. "Device Manager" These words are the best clues, in the setting package search, a lot of multi-language words of string, this is not what I am looking for, I am looking for who is using this string. Found in a layout file:

Res/xml/security_settings.xml

        <preference android:title= "@string/manage_device_admin"                    android:summary= "@string/manage_device_admin_ Summary "                    android:persistent=" false "                    android:fragment=" Com.android.settings.DeviceAdminSettings "/>

It is necessary to look at deviceadminsettings this fragment in detail. This is a more formal fragment. Very easy to understand. Key in the updatelist of this function:

    void Updatelist () {mactiveadmins.clear ();        List<componentname> cur = mdpm.getactiveadmins ();            if (cur! = null) {for (int i=0; i<cur.size (); i++) {Mactiveadmins.add (Cur.get (i));        }} mavailableadmins.clear (); list<resolveinfo> avail = getactivity (). Getpackagemanager (). Querybroadcastreceivers (New Intent (Devic eadminreceiver.action_device_admin_enabled), Packagemanager.get_meta_data |        packagemanager.get_disabled_until_used_components);        if (avail = = null) {avail = Collections.emptylist ();        }//Some admins listed in Mactiveadmins if not has been found by the above query.        We thus add them separately.        set<componentname> activeadminsnotinavail = new hashset<componentname> (mactiveadmins); for (ResolveInfo ri:avail) {componentname ricomponentname = new ComponentName (rI.activityinfo.packagename, Ri.activityInfo.name);        Activeadminsnotinavail.remove (Ricomponentname);            } if (!activeadminsnotinavail.isempty ()) {avail = new arraylist<resolveinfo> (avail);            Packagemanager Packagemanager = getactivity (). Getpackagemanager (); for (ComponentName unlistedactiveadmin:activeadminsnotinavail) {list<resolveinfo> resolved = Packa                        Gemanager.querybroadcastreceivers (New Intent (). SetComponent (Unlistedactiveadmin), Packagemanager.get_meta_data |                packagemanager.get_disabled_until_used_components);                if (resolved! = null) {Avail.addall (resolved); }}} for (int i = 0, count = avail.size (); I < count; i++) {ResolveInfo ri = Avai            L.get (i); try {deviceadmininfo dpi = new Deviceadmininfo (getactivity (), Ri);                if (dpi.isvisible () | | mactiveadmins.contains (dpi.getcomponent ())) {Mavailableadmins.add (DPI);             }} catch (Xmlpullparserexception e) {LOG.W (TAG, "skipping" + Ri.activityinfo, E);             } catch (IOException e) {LOG.W (TAG, "skipping" + Ri.activityinfo, E);    }} getlistview (). Setadapter (New Policylistadapter ()); }

The function itself is not complex. But still can not see what the so-called Device Manager is a what stuff.

The clues here need to be carefully analyzed, there seems to be two of lists:

An active list and a list of available, OK.

And what you see on the UI is exactly the same. Then you can explain that each item in the list should be a so-called Device Manager. The difference between the two lists is whether it is active.

Then look at the list of active, how it came about:

        Mactiveadmins.clear ();        List<componentname> cur = mdpm.getactiveadmins ();        if (cur! = null) {for            (int i=0; i<cur.size (); i++) {                Mactiveadmins.add (Cur.get (i));}        }

OK, get from MDPM, MDPM is Devicepolicymanager object. See here to vomit trough, Android framework in the Xxxmanager basically will be corresponding to a xxxservice, are through the typical aidl to achieve inter-process communication.

Here is also good to be expected:

    /**     * Return A list of all currently active device Administrator ' s component     * names.  Note that if there is no administrators than null may be     * returned.     */Public    list<componentname> Getactiveadmins () {        if (mservice! = null) {            try {                return Mservice.getactiveadmins (Userhandle.myuserid ());            } catch (RemoteException e) {                LOG.W (TAG, "Failed talking with device policy service", e);            }        }        return null;    }

Mservice must be the object of the Idevicepolicymanager, to find the detailed implementation is sure to find a detailed service. Devicepolicymanagerservice.

    Public list<componentname> getactiveadmins (int userhandle) {        enforcecrossuserpermission (userHandle);        Synchronized (this) {            devicepolicydata policy = getuserdata (userhandle);            Final int N = Policy.mAdminList.size ();            if (N <= 0) {                return null;            }            arraylist<componentname> res = new arraylist<componentname> (N);            for (int i=0; i<n; i++) {                Res.add (Policy.mAdminList.get (i). Info.getcomponent ());            }            return res;        }    }

First see enforcecrossuserpermission This should be required permission. A very multi-service approach checks permissions first, which is an embodiment of the Android security mechanism. It's not much to say.

Look at the logic is relatively simple, from the local list inside copied a copy to return.

See here, still do not know what this thing really is. But at least know that he is in the form of a list to keep inside the service. Then let's see how to add the list.

In this file, we found two add: one in Setactiveadmin, the same in loadsettingslocked

The most setactiveadmin found that he is a hide the excuse exists in the manager class, it seems that the third should not be transferred to, then see Loadsettingslocked Bar. Can not see this function in the XML parser, then presumably can guess, there should be an XML file exists.

    private static Journaledfile makejournaledfile (int userhandle) {        final String base = Userhandle = = 0                ? "/data/system/" + device_policies_xml                : New File (Environment.getusersystemdirectory (userhandle), DEVICE_ Policies_xml)                        . GetAbsolutePath ();        return new Journaledfile (base), new file (base + ". tmp"));    }

Look at this function and you'll probably find it. /data/system Device_policies.xml The contents of this XML without looking at the details first. What we care about is who goes back to write this file? With a corresponding savesettingslocked, tracing it can be found in the handlepackageschanged inside the call. Others have very many calls. But it doesn't look like.

Can be found when the package changes when the call to. It was also true that the page changed after the installation of a new application.

The phenomenon is explained, but still unclear, what it is for. Let's analyze it next.

About Android Device Manager-devicepolicymanager (i)