title: What's the different between start app from system launcher and custom application?
body: <p>App A has an main activity that launch mode set as standard, open it.
  When I reopen it from system launcher, everything looks normal.
  But if start app A through another app B, A restart! Why?</p>
  
  <p>My code:</p>
  
  <pre><code>Intent launchIntent = getPackageManager().getLaunchIntentForPackage("A's package name");
      launchIntent.setAction(Intent.ACTION_MAIN);
      launchIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
      launchIntent.addCategory(Intent.CATEGORY_LAUNCHER);
      startActivity(launchIntent);
  </code></pre>