這是我的Java文件

package?com.example.spinner;

import?java.util.ArrayList;
import?java.util.List;

import?android.support.v7.app.ActionBarActivity;
import?android.support.v7.app.ActionBar;
import?android.support.v4.app.Fragment;
import?android.app.Activity;
import?android.os.Bundle;
import?android.view.LayoutInflater;
import?android.view.Menu;
import?android.view.MenuItem;
import?android.view.View;
import?android.view.ViewGroup;
import?android.widget.ArrayAdapter;
import?android.widget.Spinner;
import?android.widget.TextView;
import?android.os.Build;

public?class?MainActivity?extends?Activity?{
	
	
	private?TextView?textview;
	private?Spinner?spinner;
	private?List<String>list;
	private?ArrayAdapter<String>adapter;

????@Override
????protected?void?onCreate(Bundle?savedInstanceState)?{
????????super.onCreate(savedInstanceState);
????????setContentView(R.layout.activity_main);
????????
????????textview=(TextView)?findViewById(R.id.textview);
????????spinner=(Spinner)?findViewById(R.id.spinner);
????????
????????
????????//1:設置數據源、
???????list=new?ArrayList<String>();
???????list.add("北京");
???????list.add("上海");
???????list.add("深圳");
???????list.add("廣州");
?????????//2：新建數組適配器
???????adapter=new?ArrayAdapter<String>(this,?android.R.layout.simple_spinner_item,?list);
???????//3:設置下拉列表樣式
???????adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
???????//4:加載適配器
???????spinner.setAdapter(adapter);
????????

??????
????}

}

這是我的xml文件

<?xml?version="1.0"?encoding="utf-8"?>
<LinearLayout?xmlns:android="http://schemas.android.com/apk/res/android"
????android:layout_width="match_parent"
????android:layout_height="match_parent"
????android:orientation="vertical"?>
????
????
????<TextView?
????????android:id="@+id/textview"
????????android:layout_width="match_parent"
????????android:layout_height="wrap_content"
????????android:textSize="25sp"
????????android:textColor="#ff0000"
????????/>
????
????<Spinner?
????????android:layout_width="match_parent"
????????android:layout_height="wrap_content"
????????android:id="@+id/spinner"
????????
????????
????????
????????
????????/>
????

</LinearLayout>

這是我的日志

07-18?14:52:31.343:?D/AndroidRuntime(1593):?Shutting?down?VM
07-18?14:52:31.343:?W/dalvikvm(1593):?threadid=1:?thread?exiting?with?uncaught?exception?(group=0xa61ea908)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?FATAL?EXCEPTION:?main
07-18?14:52:31.347:?E/AndroidRuntime(1593):?java.lang.RuntimeException:?Unable?to?start?activity?ComponentInfo{com.example.spinner/com.example.spinner.MainActivity}:?java.lang.NullPointerException
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.ActivityThread.access$600(ActivityThread.java:141)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.os.Handler.dispatchMessage(Handler.java:99)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.os.Looper.loop(Looper.java:137)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.ActivityThread.main(ActivityThread.java:5041)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?java.lang.reflect.Method.invokeNative(Native?Method)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?java.lang.reflect.Method.invoke(Method.java:511)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?dalvik.system.NativeStart.main(Native?Method)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?Caused?by:?java.lang.NullPointerException
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?com.example.spinner.MainActivity.onCreate(MainActivity.java:49)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.Activity.performCreate(Activity.java:5104)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	at?android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-18?14:52:31.347:?E/AndroidRuntime(1593):?	...?11?more