Q:

Enable downgrade when installing apk using intent on Android 4.2+

Is possible to enable downgrade when installing apk using intent on Android 4.2+?  I found out that it is possible, when installing app via command shell (using -d) adb install -r -d <link to apk>, so I hope it is somehow possible also via Intent. I was looking for some flag or something, but I didin't find anything helpful.
This is my intent to open package installer:
Intent intent = new Intent(Intent.ACTION_VIEW);
Uri applicatonFileUri = Uri.fromFile(applicationFile);
intent.setDataAndType(applicatonFileUri, PACKAGE_TYPE);
startActivity(intent);

A:

That's not possible for non-platform (3rd-party) apps: you have to make the installation request directly to PackageManager.
PackageManager has non-public API, installPackage() (line 2584 as of this writing):
/**
 * @hide
 *
 * Install a package. Since this may take a little while, the result will
 * be posted back to the given observer.  An installation will fail if the calling context
 * lacks the {@link android.Manifest.permission#INSTALL_PACKAGES} permission, if the
 * package named in the package file's manifest is already installed, or if there's no space
 * available on the device.
 *
 * @param packageURI The location of the package file to install.  This can be a 'file:' or a
 * 'content:' URI.
 * @param observer An observer callback to get notified when the package installation is
 * complete. {@link IPackageInstallObserver#packageInstalled(String, int)} will be
 * called when that happens.  observer may be null to indicate that no callback is desired.
 * @param flags - possible values: {@link #INSTALL_FORWARD_LOCK},
 * {@link #INSTALL_REPLACE_EXISTING}, {@link #INSTALL_ALLOW_TEST}.
 * @param installerPackageName Optional package name of the application that is performing the
 * installation. This identifies which market the package came from.
 */
public abstract void installPackage(
        Uri packageURI, IPackageInstallObserver observer, int flags,
        String installerPackageName);

where one of the possible flags is INSTALL_ALLOW_DOWNGRADE:
/**
 * Flag parameter for {@link #installPackage} to indicate that it is okay
 * to install an update to an app where the newly installed app has a lower
 * version code than the currently installed app.
 *
 * @hide
 */
public static final int INSTALL_ALLOW_DOWNGRADE = 0x00000080;

All these APIs are hidden and not accessible for 3rd-party apps. Now, you may try reflection, but I am pretty positive that platform will restrict access to them anyway.

