install / uninstall APKs programmatically (PackageManager vs Intents)

API level 14 introduced two new actions: ACTION_INSTALL_PACKAGE and ACTION_UNINSTALL_PACKAGE. Those actions allow you to pass EXTRA_RETURN_RESULT boolean extra to get an (un)installation result notification.

Example code for invoking the uninstall dialog:

String app_pkg_name = "com.example.app";
int UNINSTALL_REQUEST_CODE = 1;

Intent intent = new Intent(Intent.ACTION_UNINSTALL_PACKAGE);  
intent.setData(Uri.parse("package:" + app_pkg_name));  
intent.putExtra(Intent.EXTRA_RETURN_RESULT, true);
startActivityForResult(intent, UNINSTALL_REQUEST_CODE);

And receive the notification in your Activity#onActivityResult method:

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == UNINSTALL_REQUEST_CODE) {
        if (resultCode == RESULT_OK) {
            Log.d("TAG", "onActivityResult: user accepted the (un)install");
        } else if (resultCode == RESULT_CANCELED) {
            Log.d("TAG", "onActivityResult: user canceled the (un)install");
        } else if (resultCode == RESULT_FIRST_USER) {
            Log.d("TAG", "onActivityResult: failed to (un)install");
        }
    }
}

If you have Device Owner (or profile owner, I haven't tried) permission you can silently install/uninstall packages using device owner API.

for uninstalling:

public boolean uninstallPackage(Context context, String packageName) {
    ComponentName name = new ComponentName(MyAppName, MyDeviceAdminReceiver.class.getCanonicalName());
    PackageManager packageManger = context.getPackageManager();
    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
        PackageInstaller packageInstaller = packageManger.getPackageInstaller();
        PackageInstaller.SessionParams params = new PackageInstaller.SessionParams(
                PackageInstaller.SessionParams.MODE_FULL_INSTALL);
        params.setAppPackageName(packageName);
        int sessionId = 0;
        try {
            sessionId = packageInstaller.createSession(params);
        } catch (IOException e) {
            e.printStackTrace();
            return false;
        }
        packageInstaller.uninstall(packageName, PendingIntent.getBroadcast(context, sessionId,
                new Intent("android.intent.action.MAIN"), 0).getIntentSender());
        return true;
    }
    System.err.println("old sdk");
    return false;
}

and to install package:

public boolean installPackage(Context context,
                                     String packageName, String packagePath) {
    ComponentName name = new ComponentName(MyAppName, MyDeviceAdminReceiver.class.getCanonicalName());
    PackageManager packageManger = context.getPackageManager();
    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
        PackageInstaller packageInstaller = packageManger.getPackageInstaller();
        PackageInstaller.SessionParams params = new PackageInstaller.SessionParams(
                PackageInstaller.SessionParams.MODE_FULL_INSTALL);
        params.setAppPackageName(packageName);
        try {
            int sessionId = packageInstaller.createSession(params);
            PackageInstaller.Session session = packageInstaller.openSession(sessionId);
            OutputStream out = session.openWrite(packageName + ".apk", 0, -1);
            readTo(packagePath, out); //read the apk content and write it to out
            session.fsync(out);
            out.close();
            System.out.println("installing...");
            session.commit(PendingIntent.getBroadcast(context, sessionId,
                    new Intent("android.intent.action.MAIN"), 0).getIntentSender());
            System.out.println("install request sent");
            return true;
        } catch (IOException e) {
            e.printStackTrace();
            return false;
        }
    }
    System.err.println("old sdk");
    return false;
}

Android P+ requires this permission in AndroidManifest.xml

<uses-permission android:name="android.permission.REQUEST_DELETE_PACKAGES" />

Then:

Intent intent = new Intent(Intent.ACTION_DELETE);
intent.setData(Uri.parse("package:com.example.mypackage"));
startActivity(intent);

to uninstall. Seems easier...

This is not currently available to third party applications. Note that even using reflection or other tricks to access installPackage() will not help, because only system applications can use it. (This is because it is the low-level install mechanism, after the permissions have been approved by the user, so it is not safe for regular applications to have access to.)

Also the installPackage() function arguments have often changed between platform releases, so anything you do trying access it will fail on various other versions of the platform.

EDIT:

Also it is worth pointing out that this installerPackage was only added fairly recently to the platform (2.2?) and was originally not actually used for tracking who installed the app -- it is used by the platform to determine who to launch when reporting bugs with the app, for implementing Android Feedback. (This was also one of the times the API method arguments changed.) For at least a long while after it was introduced, Market still didn't use it to track the apps it has installed (and it may very well still not use it), but instead just used this to set the Android Feedback app (which was separate from Market) as the "owner" to take care of feedback.