intent.putExtra传递空值

Question

I am trying to develop a qr scanner where I want to show the history of scanned results to user. Now although the scanned data values are passed to a different activity properly; the problem with it is even if I have not scanned the qr the empty data is passed to the listview of the next activity.

My question is how do I make sure that only if the qr is scanned the data is passed to the next activity in the listview?

This is the code for my barcode activity.

    public class MainActivity extends AppCompatActivity implements ZXingScannerView.ResultHandler {
//Initialization
    private static final int REQUEST_CAMERA = 1;
    private ZXingScannerView mScannerView;
    ArrayList<String> listOfBarcodes = new ArrayList<String>();

//This is the part where I handle the result

     @Override
        public void handleResult(Result rawResult) {

            final String result = rawResult.getText();
            if(!result.isEmpty()) {
                //whenever you capture a new barcode add it to this list
                listOfBarcodes.add(result);
            }

PS: After this am handling the result to show in AlertDialog.

The part where I am sending the data to next activity.

 Intent data = new Intent( getApplicationContext(), History.class );
                if (listOfBarcodes!=null) {
                data.putExtra("Barcode", listOfBarcodes);
            }
                startActivity( data );

History.java

public class History extends AppCompatActivity {
public static final ArrayList completeList = new ArrayList<String>();
TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_history);
        textView = findViewById(R.id.text_view);
        Intent callingIntent= getIntent();
        ArrayList<String> listOfBarcodes = callingIntent.getExtras().getStringArrayList("Barcode");
        completeList.add(listOfBarcodes);
        ArrayAdapter<String> aA = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, completeList);
        ListView lv = (ListView) findViewById(R.id.my_list_id);
        lv.setAdapter(aA);

Apart from this I also do get the warning in completeList.add(listOfBarcodes);

Unchecked call to 'add(E)' as a member of raw type 'java.util.ArrayList' less... (Ctrl+F1) Signals places where an unchecked warning is issued by the compiler, for example:

void f(HashMap map) { map.put("key", "value"); }

In History.java the listview with empty value appears as []. Is there a different method to pass the data or am I missing something here?

Answer 1

You have to use putStringArrayListExtra() as you are sending ArrayList<String> . First make sure list listOfBarcodes has the data.

Intent data = new Intent( getApplicationContext(), History.class );
    if(listOfBarcodes.size()!=0)
    data.putStringArrayListExtra("Barcode",listOfBarcodes);
    startActivity(data);

In History Activity:-

 ListView lv = (ListView) findViewById(R.id.my_list_id);
    Intent callingIntent= getIntent();
    if(callingIntent.hasExtra("Barcode")) {
        ArrayList<String> listOfBarcodes = callingIntent.getStringArrayListExtra("Barcode");
        completeList.addAll(listOfBarcodes);
        ArrayAdapter<String> aA = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, completeList);
        lv.setAdapter(aA);
    }else{
        // No scanned handle here
    }