java - Android，如何从外部 Activity 更新ListView内容？

Question

我有一个包含 4 个类的项目:2 个 Activity 、1 个适配器和 1 个简单对象类。类的名称为:MainActivity、AddingItemsActivity、ItemAdapter、SimpleItem。在与MainActivity对应的布局中，有一个名为SimpleListView的 ListView 。 SimpleListView 应包含 SimpleItem 对象。 ItemAdapter 用于处理SimpleListView。从 MainActivity 更新、添加项目到 SimpleListView 非常容易。我想要达到的是从 AddingItemsActivity 更新、添加出现在 SimpleListView 上的项目(当用户返回到 MainActivity 时出现) )。你能告诉我我应该做什么才能达到这个目标吗？

PS:我想问:“如何从AddingItemsActivity更新SimpleListView？”但我读到这不是正确的问题，因为 SimpleListView 不存在于 AddingItemsActivity 中。

主要 Activity

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button toAddingActivity = findViewById(R.id.toAddingActivitybutton);
        final ListView simpleItemsListView = findViewById(R.id.SimpleListView);
        final ItemAdapter mAdapter = new ItemAdapter(this, R.layout.simple_item_adapter);


        toAddingActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getBaseContext(), AddingItemsActivity.class);
                startActivity(intent);
            }
        });    
    }
} 

添加项目 Activity

public class AddingItemsActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_adding_items);
        Button addItem = findViewById(R.id.AddItembutton);
//        final ListView simpleItemsListView = findViewById(R.id.SimpleListView);
//        final ItemAdapter mAdapter = new ItemAdapter(this, R.layout.simple_item_adapter);



        addItem.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//                first reflex try, which does not work:

//                SimpleItem item = new SimpleItem("String number 1", "String number 2");
//                mAdapter.add(item);
//                simpleItemsListView.setAdapter(mAdapter);
            }
        });
    }
}

项目适配器

public class ItemAdapter extends ArrayAdapter<SimpleItem>{
    public  ItemAdapter(Context context, int textViewResourceId) {
        super(context, textViewResourceId);
    }
    public ItemAdapter(Context context, int resource, List<SimpleItem> items) {
        super(context, resource, items);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View v = convertView;

        if (v == null) {
            LayoutInflater vi;
            vi = LayoutInflater.from(getContext());
            v = vi.inflate(R.layout.simple_item_adapter, null);
        }

        SimpleItem  item = getItem(position);

        if (item != null) {
            TextView tv1 = v.findViewById(R.id.adapterTextView1);
            TextView tv2 = v.findViewById(R.id.adapterTextView2);

            tv1.setText(item.getStr1());
            tv2.setText(item.getStr2());
        }
        return v;
    }
}

简单项目

public class SimpleItem {
    private String str1;
    private String str2;


    public SimpleItem(String s1, String s2)
    {
        str1 = s1;
        str2 = s2;
    }

    public String getStr1()
    {
        return str1;
    }


    public String getStr2()
    {
        return str2;
    }


}

Answer 1

1. 使用startActivityForResult从AddingItemsActivity获取SimpleItem结果。

   Intentintent = new Intent(getBaseContext(),AddingItemsActivity.class);
startActivityForResult(intent,1);

2. 在AddingItemsActivity中创建一个SimpleItem，向其添加值并使用setResult将简单项目实例返回给MainActivity

   // inside on click
   SimpleItem item = new SimpleItem("String number 1", "String number 2");
   Intent returnIntent = new Intent();
   returnIntent.putExtra("result", item);
   setResult(Activity.RESULT_OK,returnIntent);
   finish();`
   

3. 在主 Activity 中

   @Override
   protected void onActivityResult(int requestCode, int resultCode, Intent data) {
   
   if (requestCode == 1) {
       if(resultCode == Activity.RESULT_OK){
           SimpleItem result = (SimpleItem)data.getSerializableExtra("result");
           // add result to the list, used by adapter
           // notify adapter using notifyDataSetChanged
       }
   }
   }//onActivityResult
   

注意:添加public class SimpleItem Implements Serialized并且似乎您忘记创建列表并将其传递给适配器实例，因此只需创建它即可