Android：当我从其他活动传递数据时，ListView没有更新

Question

I am new to android and i am making listview based app. In my app i have items from Acitity_2 to Activity_1. Activity_1 has the list view. when user click on ADD button of activity1 then Activity_2 will be called. Activity_2 has the EditText. The value of EditText should update the ListView. But it only takes last value of the Edittext.

Here is the code of Activity_2:

          Intent intent = new Intent(ItemDetails.this, MainActivity.class);
          intent.putExtra("values", values);
          startActivity(intent);

Code for Activity_1

          ArrayList<String> list = new ArrayList<String>();

/** Declaring an ArrayAdapter to set items to ListView */
ArrayAdapter<String> adapter;

protected Context context;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    /** Setting a custom layout for the list activity */
    setContentView(R.layout.activity_main);

    /** Reference to the add button of the layout main.xml */
    Button btn = (Button) findViewById(R.id.btnAdd);

    /** Reference to the delete button of the layout main.xml */
    Button btnDel = (Button) findViewById(R.id.btnDel);




    /** Defining the ArrayAdapter to set items to ListView */
   adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_multiple_choice, list);
    list.clear();
   list.add("Aluminium foil");
   /** Setting the adapter to the ListView */
   setListAdapter(adapter);

   String val="";
   if(getIntent().getStringExtra("values")!=null &&    getIntent().getStringExtra("values").length() > 0){
       val = getIntent().getStringExtra("values");
       list.add(val);
  }                    

   adapter.notifyDataSetChanged();

Now its overriding last value of edittext. Suggestions are appreciated.

Answer 1

Any good ??

Set adapter first time as

adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_multiple_choice, list);
listView.setAdapter(adapter);

on coming back from Activity 2

 String val="";
         if(getIntent().getStringExtra("values")!=null &&    getIntent().getStringExtra("values").length > 0){
    val = getIntent().getStringExtra("values");
    list.add(val);
        }                    

adapter.notifyDataSetChanged();

you basically dont have to create a new adapter object each time you come back

Answer 2

You should start second Activity with startActivityForResult. Then insert the value in the editext and finishing the activity sending back the result. In activity1 intercept the result in the methos onActivityResult and update the listview.

Check out this link about activity results: http://developer.android.com/training/basics/intents/result.html

Answer 3

为了让Android更新您的listview，您需要在Adapter上调用notifyDataSetChanged() 。

Answer 4

It's not enough to simply update your data set, you have to let the Adapter know so it reads the data again and updates the list. I can't see what your adapter is called from your code, but just call notifyDataSetChanged() on your adapter and it should work.

Answer 5

有很多方法可以实现……但是最好的最简单的解决方案是使用：refreshDisplay（）;

Answer 6

Do this,

String itemVal=getIntent().getStringExtra("values");
            if(itemVal==null){

            }else{
                list.add(itemVal);

            }
adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_multiple_choice, list);