微调器在弹出窗口中不工作-Android

我有一个弹出窗口，要求您输入一些信息，然后使用

微调器选择一个状态。我可以将
微调器
放在
xml
中，它显示得很好，但是当我尝试激活
微调器
时，它会使应用程序崩溃。下面是我用来创建
微调器的代码

public class DashboardActivity extends ListActivity implements OnItemSelectedListener {
    private TextView state_selection;
    private static final String[] items = {
        "Select State of Driver",
            "Alabama",
            "Alaska",
            "Arizona",
            "Arkansas",
            "California",
            "Colorado",
            "Connecticut",
            "Delaware",
            "District of Columbia",
            "Florida",
            "Georgia",
            "Hawaii",
            "Idaho",
            "Illinois",
            "Indiana",
            "Iowa",
            "Kansas",
            "Kentucky",
            "Louisiana",
            "Maine",
            "Maryland",
            "Massachusetts",
            "Michigan",
            "Minnesota",
            "Mississippi",
            "Missouri",
            "Montana",
            "Nebraska",
            "Nevada",
            "New Hampshire",
            "New Jersey",
            "New Mexico",
            "New York",
            "North Carolina",
            "North Dakota",
            "Ohio",
            "Oklahoma",
            "Oregon",
            "Pennsylvania",
            "Puerto Rico",
            "Rhode Island",
            "South Carolina",
            "South Dakota",
            "Tennessee",
            "Texas",
            "Utah",
            "Vermont",
            "Virginia",
            "Washington",
            "West Virginia",
            "Wisconsin",
            "Wyoming"
    };

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.xmlfile);

        state_selection = (TextView) findViewById(R.id.state_selection);
        Spinner my_spin = (Spinner) findViewById(R.id.state_spinner);
        my_spin.setOnItemSelectedListener(this);
        ArrayAdapter aa = new ArrayAdapter(this, android.R.layout.simple_spinner_item, items);
        aa.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        my_spin.setAdapter(aa);
    }

    @Override
    public void onItemSelected(AdapterView arg0, View arg1, int pos, long arg3) {
        state_selection.setText(items[pos]);
    }

    @Override
    public void onNothingSelected(AdapterView arg0) {
        // TODO Auto-generated method stub
        state_selection.setText("");
    }
}

这是我的
Logcat

07-20 13:28:25.535: E/AndroidRuntime(1378): FATAL EXCEPTION: main
07-20 13:28:25.535: E/AndroidRuntime(1378): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.DashboardActivity}: java.lang.NullPointerException
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.ActivityThread.access$600(ActivityThread.java:139)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.os.Looper.loop(Looper.java:154)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.ActivityThread.main(ActivityThread.java:4945)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at java.lang.reflect.Method.invokeNative(Native Method)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at java.lang.reflect.Method.invoke(Method.java:511)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at dalvik.system.NativeStart.main(Native Method)
07-20 13:28:25.535: E/AndroidRuntime(1378): Caused by: java.lang.NullPointerException
07-20 13:28:25.535: E/AndroidRuntime(1378):     at com.example.DashboardActivity.onCreate(DashboardActivity.java:160)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.Activity.performCreate(Activity.java:4531)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071)
07-20 13:28:25.535: E/AndroidRuntime(1378):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)

7-20 13:28:25.535:E/AndroidRuntime（1378）：由以下原因引起：
java.lang.NullPointerException

你忘了加上

setContentView（R.layout.layout\u name）
after
super.onCreate（savedInstanceState）
检查您的

@Override
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
        long arg3) {
    // TODO Auto-generated method stub

}

@覆盖
已选择公共视图（适配器视图arg0、视图arg1、内部arg2、，
长arg3）{
//TODO自动生成的方法存根
}
请参阅第160行。您在该行发生崩溃。您认为错误是否可能是因为my_spin.setOnItemSelectedListener（此）；你在用“这个”吗？当微调器实际位于弹出式布局中而不是主布局中时？确定，然后将代码放入其中，在单击项目后，您将对其执行操作@user2544045您的代码是准确的，您现在是否收到相同的异常？