ListView 适配器在添加项目时的工作

Question

I am new to the android development and have got a doubt about the working of setAdapter and ListView .

My MainActivity.java looks like below:

public class MainActivity extends AppCompatActivity {
    private Button generate_btn;
    private ArrayList<Integer> arr;
    private Random rand_generator;
    private ListView listView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        arr = new ArrayList<Integer>();
        setContentView(R.layout.activity_main);
        for(int i = 0; i < 5; i++){
            arr.add(i);
        }
        generate_btn = findViewById(R.id.button);
        
        ArrayAdapter<Integer> adapter = new ArrayAdapter<Integer>(getApplicationContext(), android.R.layout.simple_list_item_1, arr);
        listView = findViewById(R.id.listView);
        listView.setAdapter(adapter);

        for(int i = 0; i < 5; i++){
            arr.add(i + 100);
        }

As we can see above that I have two for loops, the first one adds integers till 5 to the ArrayList<Integer> arr and then I am calling the setAdapter on the listView . Till here arr only contains the integers till 5.

In the second loop, I am adding integers from 100 to 104 but not calling notifyDataSetChanged() .

I expected that the rendered result will contain TextViews till 5 only since I have set the adapter when arr was having elements till 5. But to my surprise, the result was having TextViews of integers added in the second for loop also.

What am I missing here?

Answer 1

Adapter maintains the reference to arr . So even if we are updating the ArrayList after the setAdapter(..) the size is getting updated accordingly and it can be cross-checked by putting a print statement of arr.size() in getView(..) method of a CustomAdapter .

getView(..) is called by listView in various cases till adapter.getItemCount() is more than the internal integer pointer.