按下后退按钮时如何调用QR码扫描仪？

Question

Let's say my app have these requirements:

1. First display login screen (if no login session is detected on SQLite)
2. If login is success, display QR code scanning screen (full screen)
3. If scanning is success, store the result on SQLite and display them on the Product screen
4. If you are in Product Screen and presses back, immediately the QR code scanning screen appears. And so on.

Here's my code (irrelevant parts are ommited).

LoginActivity.java

public class LoginActivity extends AppCompatActivity {

    private EditText edtUsername;
    private EditText edtPassword;
    private Button btnLogin;

    // store username & password in SQLite db
    // taken from https://www.androidhive.info/2012/08/android-session-management-using-shared-preferences/
    SessionManager session;

    // manage stored items in SQLite
    private DatabaseHelper db;

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

        spinner.setAdapter(adapter);

        db = new DatabaseHelper(this);

        session = new SessionManager(getApplicationContext());
        if (session.isLoggedIn()){
            IntentIntegrator scanIntegrator = new IntentIntegrator(LoginActivity.this);
            scanIntegrator.setOrientationLocked(false);
            scanIntegrator.initiateScan();
        }

        edtUsername = (EditText) findViewById(R.id.edtName);
        edtPassword = (EditText) findViewById(R.id.edtPassword);
        btnLogin = (Button) findViewById(R.id.btnLogin);
    }


    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        IntentResult scanningResult = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if (scanningResult != null){
            String scanContent = scanningResult.getContents();
            String[] data = parseContent(scanContent);

            db.insertItem(new Item(data[0], data[1], data[2]));

            Intent iii = new Intent(LoginActivity.this, ScanResultActivity.class);
            startActivity(iii);
        }
    }

}

ScanResultActivity.java

public class ScanResultActivity extends AppCompatActivity {

    private RecyclerView recView;
    private ItemAdapter mAdapter;
    private DatabaseHelper db;
    private List<Item> itemList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scan_result);

        recView = (RecyclerView) findViewById(R.id.recycler_view);
        itemList = new ArrayList<>();

        db = new DatabaseHelper(this);
        itemList.addAll(db.getAllItems());

        mAdapter = new ItemAdapter(this, itemList);
        RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
        recView.setLayoutManager(mLayoutManager);
        recView.setItemAnimator(new DefaultItemAnimator());
        recView.addItemDecoration(new MyDividerItemDecoration(this, LinearLayoutManager.VERTICAL, 16));
        recView.setAdapter(mAdapter);
    }
}

Part 1 - 3 run fine. The only issue is once you are in 4 and press the back button, you'll jump to Login activity on its "not login state", so you have to repeat the login process. What I want, instead, is run the QR code scanning part again. How to do this?

Answer 1

You could isolate your login screen. Instead of only two activities, you could have three: LoginActivity -> QRCodeScanActivity -> ScanResultActivity .

This way if the user presses the back button he is going back to QRCodeScanActivity .

Answer 2

in onBackPressed(); method just call finesh() method you will be go back on QRCodeScanActivity