Android旋转器 - 无法解决符号-SetOnitemSelectedListener

Question

我是Android编程的新手，我正在尝试实现旋转器，但是我会为SetOnItemSelectedListener，SetDropDownViewResource和SetAdapter遇到"无法解决"无法解决"符号。我很难过。我试图添加更多导入，但他们什么都没做。

这是我的代码：

public class MainActivity extends AppCompatActivity implements OnItemSelectedListener {
    public final static String EXTRA_MESSAGE = "com.example.FinalProject.MESSAGE";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    Spinner spinner = (Spinner) findViewById(R.id.spinner);
    spinner.setOnItemSelectedListener(this);
// Create an ArrayAdapter using the string array and a default spinner layout
    ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.verb_endings_array, android.R.layout.simple_spinner_item);
// Specify the layout to use when the list of choices appears
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Apply the adapter to the spinner
    spinner.setAdapter(adapter);
    public void onItemSelected(AdapterView<?> parent, View view,
                           int pos, long id) {
        // An item was selected. You can retrieve the selected item using
        // parent.getItemAtPosition(pos)
    }
    public void onNothingSelected(AdapterView<?> parent) {
        // Another interface callback
    }
    /** Called when the user clicks the Send button */
    public void sendMessage(View view) {
        Intent intent = new Intent(this, DisplayMessageActivity.class);
        EditText editText = (EditText) findViewById(R.id.edit_message);
        String message = editText.getText().toString();
        intent.putExtra(EXTRA_MESSAGE, message);
        startActivity(intent);
    }
}    

Answer 1

移动此

Spinner spinner = (Spinner) findViewById(R.id.spinner);
spinner.setOnItemSelectedListener(this);

在内部方法，但是在外面声明旋转器（您需要稍后使用它...：）

private Spinner spinner;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    spinner = (Spinner) findViewById(R.id.spinner);
    spinner.setOnItemSelectedListener(this);
}