java - 使用 Intent 发送和接收 Arraylist？安卓

Question

我正在尝试创建一个国家列表，该列表将由用户在运行时添加。

我正在使用 intent & adapter 和 listview 来显示国家/地区。

当 Activity 开始“我的国家”用户点击按钮添加国家时，一个新的 Activity 将开始“添加国家”，我的问题是为什么我在列表中看不到任何国家？我发送和接收正确吗？MyCountries 的代码:

public class MyCountries extends Activity {



private ListView lv;
private ArrayAdapter<String> adapter;
private ArrayList<String>list;


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

    //Button compute=(Button)findViewById(R.id.cancel);

    lv=(ListView)findViewById(R.id.listView1);

    list=new ArrayList<String>();

    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);
    lv.setAdapter(adapter);



    Intent i = getIntent();  

    list = i.getStringArrayListExtra("country&year");

    adapter.notifyDataSetChanged();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.my_countries, menu);
    return true;
}
public void onClick(View v) {

    Intent intent = new Intent(v.getContext(), AddCountry.class);
    startActivityForResult(intent,1);
}

“AddCountry”代码

public class AddCountry extends Activity {
private EditText name;
private EditText year;
public String country_name;
public int visited_year;
public ArrayList<String>arr;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_add_country);
    name = (EditText) findViewById(R.id.country);

    year = (EditText) findViewById(R.id.year);
    arr= new ArrayList<String>();
    Button button=(Button)findViewById(R.id.add);
}



public void onClick(View v) {

    switch (v.getId()) {
    case R.id.add:
        //Toast.makeText(this, "Add was clicked", Toast.LENGTH_LONG).show();
        //new activity
        Intent sending = new Intent();

        country_name = name.getText().toString();
        visited_year = Integer.parseInt(year.getText().toString());

        for(int i=0;i<arr.size();i++){
            arr.add(country_name+""+visited_year);
            //startActivity(sending);
        }
        sending.putStringArrayListExtra("country&year", arr);

    }
}

Answer 1

您正在向适配器发送空列表:

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

adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);

//在初始化您的适配器之前从 Intent (到您的列表)获取数据，您不需要通知

  list = i.getStringArrayListExtra("country&year");

       adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);
        lv.setAdapter(adapter);