如何获取微调器中选定项目的值？

Question

我刚学Android应用开发，不明白怎么Logspinner中选中项的值。

这是我为MainActivity.java 准备的内容

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responding to user selections 上的 Android 开发文档，但使用我的代码时，我收到此错误：Could not resolve symbol setOnItemSelectedListener

为什么？我该如何解决它，以便我可以 Log 在 Spinner 中选择什么？

编辑

此代码有效

package com.example.compy.spookr;

公共类 MainActivity 扩展 ActionBarActivity 实现 AdapterView.OnItemSelectedListener { 公共微调器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

首先，你需要实现interface你想要使用的方法。在你的情况下，你可以这样做：

public class MainActivity extends ActionBarActivity implements OnItemSelectedListener{

然后，将@Override 放在描述您想要的行为的方法上：

  @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 onCreate() 中设置您的微调器侦听器：

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

Answer 2

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

在MainActivity 中实现OnItemSelectedListener 接口：

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

在 onCreate 方法中将 setOnItemSelectedListener 添加到 Spinner ：

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..
}

并且在为当前 Activity 设置布局后还调用 findViewById，因为来自 xml 的视图仅在为 Activity 设置布局后可用，否则应用程序将因 NPE 而崩溃

Answer 3

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)
    }
}