Android：当所有程序发送到后台时，如何关闭从我的应用程序打开的应用程序

Question

Here is my problem. I am developing app that loads some documents from server. I open document in another app via Intent.ACTION_VIEW. This is all working just fine. Problem is that whole app is pin protected so I have to capture events such "sent to background" or "screen lock" to bring up pin screen afterwards and this is not working when another app is opened above mine. So if user opens document then press home button, click on my launch icon from menu then he gets again external app with opened document and with back button access my app again. This is security issue that needs to be fixed. Here are some code snippets:

---

Opening document:

Intent intent = new Intent();
intent.setAction(Intent.ACTION_VIEW);

Uri uri = Uri.fromFile(downloadedFile);
String mimeType = document.getMimeType();
intent.setDataAndType(uri, mimeType);
startActivityForResult(intent, 1);

capture sent to background:

        ActivityManager am = (ActivityManager) context
            .getSystemService(Context.ACTIVITY_SERVICE);
    List<RunningTaskInfo> tasks = am.getRunningTasks(1);
    if (!tasks.isEmpty()) {
        ComponentName topActivity = tasks.get(0).topActivity;
        if (!topActivity.getPackageName().equals(context.getPackageName())) {
            IN_BACKGROUND = true;
            Log.i(PinUtil.class.getSimpleName(), "App sent to background ");
        } else {
            IN_BACKGROUND = false;
        }
    }

My question is: Is it possible to detect if my app is sent to background when another app is opened? How not to open another app when my launcher icon is pressed.

Thanks for all responses. Regards Lubos

Answer 1

In order to fix this problem:

So if user opens document then press home button, click on my launch icon from menu then he gets again external app with opened document and with back button access my app again. This is security issue that needs to be fixed. Here are some code snippets:

You need to make sure that, when you launch an external app for the user to view a document, that the external app does not run in the same task as your application. It needs to run in a new, separate task. You can do this like this:

Intent intent = new Intent();
intent.setAction(Intent.ACTION_VIEW);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); // Ensure app runs in separate task
Uri uri = Uri.fromFile(downloadedFile);
String mimeType = document.getMimeType();
intent.setDataAndType(uri, mimeType);
startActivity(intent); // Can't use startActivityForResult() here

However, you can't use startActivityForResult() when you launch the external viewer, because an activity running in another task cannot return a result to you. However, most external applications won't return a result when launched with ACTION_VIEW anyway, so it probably isn't a problem.

Then you asked this:

My question is: Is it possible to detect if my app is sent to background when another app is opened? How not to open another app when my launcher icon is pressed.

There should be some answers on StackOverflow that can help you determine if your application is in the background (it isn't actually that easy to determine this).

My explanation above should answer your 2nd question. If you don't launch other apps in your task, then only your app will be launched when your launcher icon is pressed.