/**
 * Offers the ability to install, upgrade, and remove applications on the
 * device. This includes support for apps packaged either as a single
 * "monolithic" APK, or apps packaged as multiple "split" APKs.
 * <p>
 * An app is delivered for installation through a
 * {@link PackageInstaller.Session}, which any app can create. Once the session
 * is created, the installer can stream one or more APKs into place until it
 * decides to either commit or destroy the session. Committing may require user
 * intervention to complete the installation.
 * <p>
 * Sessions can install brand new apps, upgrade existing apps, or add new splits
 * into an existing app.
 * <p>
 * Apps packaged as multiple split APKs always consist of a single "base" APK
 * (with a {@code null} split name) and zero or more "split" APKs (with unique
 * split names). Any subset of these APKs can be installed together, as long as
 * the following constraints are met:
 * <ul>
 * <li>All APKs must have the exact same package name, version code, and signing
 * certificates.
 * <li>All APKs must have unique split names.
 * <li>All installations must contain a single base APK.
 * </ul>
 * <p>
 * ###########此处告诉开发者如何调用API安装apk##############
 * The ApiDemos project contains examples of using this API:
 * <code>ApiDemos/src/com/example/android/apis/content/InstallApk*.java</code>.  
 */
public class PackageInstaller

package com.example.android.apis.content;

// Need the following import to get access to the app resources, since this
// class is in a sub-package.
import com.example.android.apis.R;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentSender;
import android.content.pm.PackageInstaller;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;


/**
 * Demonstration of package installation and uninstallation using the package installer Session
 * API.
 *
 * @see InstallApk for a demo of the original (non-Session) API.
 */
public class InstallApkSessionApi extends Activity {
  private static final String PACKAGE_INSTALLED_ACTION =
      "com.example.android.apis.content.SESSION_API_PACKAGE_INSTALLED";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.install_apk_session_api);

    // Watch for button clicks.
    Button button = (Button) findViewById(R.id.install);
    button.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
        PackageInstaller.Session session = null;
        try {
          PackageInstaller packageInstaller = getPackageManager().getPackageInstaller();
          PackageInstaller.SessionParams params = new PackageInstaller.SessionParams(
              PackageInstaller.SessionParams.MODE_FULL_INSTALL);
          int sessionId = packageInstaller.createSession(params);
          session = packageInstaller.openSession(sessionId);

          addApkToInstallSession("HelloActivity.apk", session);

          // Create an install status receiver.
          Context context = InstallApkSessionApi.this;
          Intent intent = new Intent(context, InstallApkSessionApi.class);
          intent.setAction(PACKAGE_INSTALLED_ACTION);

          //此处也可以使用getBoradcast或者getService回调通知
          PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, 0);
          IntentSender statusReceiver = pendingIntent.getIntentSender();

          // Commit the session (this will start the installation workflow).
          session.commit(statusReceiver);
        } catch (IOException e) {
          throw new RuntimeException("Couldn't install package", e);
        } catch (RuntimeException e) {
          if (session != null) {
            session.abandon();
          }
          throw e;
        }
      }
    });
  }

  private void addApkToInstallSession(String assetName, PackageInstaller.Session session)
      throws IOException {
    // It's recommended to pass the file size to openWrite(). Otherwise installation may fail
    // if the disk is almost full.
    try (OutputStream packageInSession = session.openWrite("package", 0, -1);
       InputStream is = getAssets().open(assetName)) {
      byte[] buffer = new byte[16384];
      int n;
      while ((n = is.read(buffer)) >= 0) {
        packageInSession.write(buffer, 0, n);
      }
    }
  }

  // Note: this Activity must run in singleTop launchMode for it to be able to receive the intent
  // in onNewIntent().
  @Override
  protected void onNewIntent(Intent intent) {
    Bundle extras = intent.getExtras();
    if (PACKAGE_INSTALLED_ACTION.equals(intent.getAction())) {
      int status = extras.getInt(PackageInstaller.EXTRA_STATUS);
      String message = extras.getString(PackageInstaller.EXTRA_STATUS_MESSAGE);

      switch (status) {
        case PackageInstaller.STATUS_PENDING_USER_ACTION:
          // This test app isn't privileged, so the user has to confirm the install.
          Intent confirmIntent = (Intent) extras.get(Intent.EXTRA_INTENT);
          startActivity(confirmIntent);
          break;

        case PackageInstaller.STATUS_SUCCESS:
          Toast.makeText(this, "Install succeeded!", Toast.LENGTH_SHORT).show();
          break;

        case PackageInstaller.STATUS_FAILURE:
        case PackageInstaller.STATUS_FAILURE_ABORTED:
        case PackageInstaller.STATUS_FAILURE_BLOCKED:
        case PackageInstaller.STATUS_FAILURE_CONFLICT:
        case PackageInstaller.STATUS_FAILURE_INCOMPATIBLE:
        case PackageInstaller.STATUS_FAILURE_INVALID:
        case PackageInstaller.STATUS_FAILURE_STORAGE:
          Toast.makeText(this, "Install failed! " + status + ", " + message,
              Toast.LENGTH_SHORT).show();
          break;
        default:
          Toast.makeText(this, "Unrecognized status received from installer: " + status,
              Toast.LENGTH_SHORT).show();
      }
    }
  }
}

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