black screen appears when come back from an external application

问题

I have an application that open an external application to read PDF files. here is the code to open the external app.

        if(file!=null){
            PackageManager packageManager = getPackageManager();
            Intent testIntent = new Intent(Intent.ACTION_VIEW);
            testIntent.setType("application/pdf");
            List list = packageManager.queryIntentActivities(testIntent, PackageManager.MATCH_DEFAULT_ONLY);
            if (list.size() > 0 && file.isFile()) {
                Intent intent = new Intent();
                intent.setAction(Intent.ACTION_VIEW);
                Uri uri = Uri.fromFile(file);
                intent.setDataAndType(uri, "application/pdf");

                startActivity(intent);
            }else{
            Toast.makeText(this, "problem loading file", Toast.LENGTH_LONG).show();
        }
        }

The problem is when I come back from my pdf application (adobe reader or any pdf reader app), in the first click of my back button I get a black screen and in second I can reach my activity? How could I possibly solve this problem?

回答1:

I think this is probably the normal Activity lifecycle at work.

Once your Activity goes into the background, it is deemed no longer critical by the OS and its process may be killed in order to reclaim memory or resources for a foreground Activity. The black screen you see when pressing the back button is the window background of your application's theme which appears while your Activity is recreated and its state is restored.

This is normal behavior. Ensure that your Activity saves and restores its state efficently by implementing the appropriate lifecycle methods to reduce the time it takes to re-create.

See http://developer.android.com/reference/android/app/Activity.html#ActivityLifecycle

来源：https://stackoverflow.com/questions/9002322/black-screen-appears-when-come-back-from-an-external-application