java - 如何获取 setOnItemSelectedListener 之外的变量的更新值？

Question

我想做什么？

我正在尝试获取 OnItemSelectedListener 之外的数据成员 totalPrice 的值，该值由函数 在 OnItemSelectedListener 内部更新填充()。

代码:

主要 Activity

public class MainActivity extends AppCompatActivity {

   private double totalPrice;
   private void populate(){
      // some private code
      totalPrice += 10; // this shows the updated value
   }

   private void initSpinner(){

      Spinner date = findViewById(R.id.Date);

      ArrayList<String> dateContent = new ArrayList<>();
      dateContent.add("2020-06");
      dateContent.add("2020-05");

      ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.date_layout, R.id.dateItem, dateContent);
      date.setAdapter(adapter);

      date.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener(){
          @Override
          public void onItemSelected(AdapterView adapter, View view, int i, long lng){
              for (int idx = 0; idx < 5; idx++)
                  populate();
          }
          @Override
          public void onNothingSelected(AdapterView<?> parentView){ }
      });
  }

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      initSpinner();
      System.out.println("Total: "+totalPrice); // this doesn't show updated value
  }
}

Answer 1

您无法在 onCreate 中获取更新的值，因为它仅在创建 Activity 时调用一次。要获取最新值，您可以尝试此操作

public class MainActivity extends AppCompatActivity {

   private double totalPrice;
   private void populate(){
      // some private code
      totalPrice += 10; // this shows the updated value
      System.out.println("Total: "+totalPrice); 
   }

   private void initSpinner(){

      Spinner date = findViewById(R.id.Date);

      ArrayList<String> dateContent = new ArrayList<>();
      dateContent.add("2020-06");
      dateContent.add("2020-05");

      ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.date_layout, R.id.dateItem, dateContent);
      date.setAdapter(adapter);

      date.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener(){
          @Override
          public void onItemSelected(AdapterView adapter, View view, int i, long lng){
              for (int idx = 0; idx < 5; idx++)
                  populate();
          }
          @Override
          public void onNothingSelected(AdapterView<?> parentView){ }
      });
  }

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

  }
}