如何获得微调器中选定项目的值？

Question

我只是在学习Android应用程序开发，还不了解如何Log微调器中所选项目的值。

这是MainActivity.java

import android.content.ContentResolver;
import android.database.Cursor;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.provider.ContactsContract;

import java.util.ArrayList;

    public class MainActivity extends ActionBarActivity {
        public Spinner contactSpinner = (Spinner) findViewById(R.id.contact_list);

    protected void onCreate(Bundle savedInstanceState) {
        ArrayList contactList = new ArrayList();

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        contactList.add("An item");  
        contactList.add("Another item");  
        contactList.add("A third item");  

        // Add items from contactList to spinner
        ArrayAdapter adapter = new ArrayAdapter(this,android.R.layout.simple_spinner_dropdown_item,contactList);
        contactSpinner.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
    }

    contactSpinner.setOnItemSelectedListener(this);  
}

我正在关注Android开发文档，以响应用户选择 ，但是使用我的代码，我收到此错误： Could not resolve symbol setOnItemSelectedListener

为什么？ 以及如何解决它，以便可以Log微调器中选择的内容？

编辑

此代码有效

package com.example.compy.spookr;

公共类MainActivity扩展ActionBarActivity实现AdapterView.OnItemSelectedListener {public Spinner contactSpinner;

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

    ArrayList contactList = new ArrayList();
    contactSpinner = (Spinner) findViewById(R.id.contact_list);
    contactSpinner.setOnItemSelectedListener(this);
    // Rest of code...
}

@Override
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);
    Log.v("onItemSelected",(String) parent.getItemAtPosition(pos));
}

@Override
public void onNothingSelected(AdapterView<?> parent) {
    // Another interface callback
}

// Rest of code ... 

}

Answer 1

我收到此错误：无法解析符号setOnItemSelectedListener

在MainActivity实现OnItemSelectedListener接口：

public class MainActivity extends ActionBarActivity 
                              implements OnItemSelectedListener{
  ....
}

将setOnItemSelectedListener添加到onCreate方法内的Spinner中：

public Spinner contactSpinner;
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    contactSpinner = (Spinner) findViewById(R.id.contact_list);
    contactSpinner.setOnItemSelectedListener(this);  
     //... your code here..
}

并在设置当前Activity的布局后也调用findViewById ，因为只有在为Activity设置布局后，才能使用xml中的视图，否则应用程序将因NPE崩溃

Answer 2

您可以使用getSelectedItem（）方法：

Spinner spinner = (Spinner)findViewById(R.id.spinner);
String selected = spinner.getSelectedItem().toString();

或使用getItemAtPosition（）方法：

public class SpinnerActivity extends Activity implements OnItemSelectedListener {
    ...
    @Override
    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)
    }
}

Answer 3

首先，您需要实现要使用这些方法的interface 。 在您的情况下，您可以这样做：

public class MainActivity extends ActionBarActivity implements OnItemSelectedListener{

然后，将@Override放在描述所需行为的方法上：

  @Override
  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);

}

   @Override
  public void onNothingSelected(AdapterView<?> parent) {
// Another interface callback

}

然后在您的onCreate()设置您的微调监听器：

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
contactSpinner = (Spinner) findViewById(R.id.contact_list);
contactSpinner.setOnItemSelectedListener(this);  
....