这运行时正常的，就是一大段错误....能告诉我怎么回事吗？
package com.example.viewpagerdemo;
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends Activity implements View.OnClickListener {
private LinearLayout mWeiXin;
private LinearLayout mFriend;
private LinearLayout mContact;
private LinearLayout mSetting;
private ImageButton mImgWeixin;
private ImageButton mlmgFriend;
private ImageButton mImgContact;
private ImageButton mImgSetting;
private PagerAdapter adapter;
private LayoutInflater mInflater;
private List<View> views = new ArrayList<View>();
private ViewPager viewpager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
initView();
viewpager.setAdapter(adapter);
initEvent();
}
private void initEvent() {
mWeiXin.setOnClickListener(this);
mContact.setOnClickListener(this);
mFriend.setOnClickListener(this);
mSetting.setOnClickListener(this);
viewpager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
resetImg();
switch (position) {
case 0:
mImgWeixin.setImageResource(R.mipmap.tab_weixin_pressed);
break;
case 1:
mlmgFriend.setImageResource(R.mipmap.tab_find_frd_pressed);
break;
case 2:
mImgContact.setImageResource(R.mipmap.tab_address_pressed);
break;
case 3:
mImgSetting.setImageResource(R.mipmap.tab_settings_pressed);
break;
}
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
private void initView() {
viewpager = (ViewPager) findViewById(R.id.viewPager);
mWeiXin = (LinearLayout) findViewById(R.id.weixin);
mFriend = (LinearLayout) findViewById(R.id.Friend);
mContact = (LinearLayout) findViewById(R.id.Contact);
mSetting = (LinearLayout) findViewById(R.id.setting);
mImgWeixin = (ImageButton) findViewById(R.id.img_weixin);
mImgContact = (ImageButton) findViewById(R.id.img_Contact);
mlmgFriend = (ImageButton) findViewById(R.id.img_Friend);
mImgSetting = (ImageButton) findViewById(R.id.img_setting);
mImgWeixin.setImageResource(R.mipmap.tab_weixin_pressed);
mInflater = LayoutInflater.from(MainActivity.this);
View view01 = mInflater.inflate(R.layout.tab01, null);
View view02 = mInflater.inflate(R.layout.tab02, null);
View view03 = mInflater.inflate(R.layout.tab03, null);
View view04 = mInflater.inflate(R.layout.tab04, null);
views.add(view01);
views.add(view02);
views.add(view03);
views.add(view04);
adapter = new PagerAdapter() {
@Override
public int getCount() {
return views.size();
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView(views.get(position));
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
View view = views.get(position);
container.addView(view);
return view;
}
};
}
@Override
public void onClick(View view) {
resetImg();
switch (view.getId()) {
case R.id.weixin:
viewpager.setCurrentItem(0);
mImgWeixin.setImageResource(R.mipmap.tab_weixin_pressed);
break;
case R.id.Friend:
viewpager.setCurrentItem(1);
mlmgFriend.setImageResource(R.mipmap.tab_find_frd_pressed);
break;
case R.id.Contact:
viewpager.setCurrentItem(2);
mImgContact.setImageResource(R.mipmap.tab_address_pressed);
break;
case R.id.setting:
viewpager.setCurrentItem(3);
mImgSetting.setImageResource(R.mipmap.tab_settings_pressed);
break;
}
}
private void resetImg() {
mImgWeixin.setImageResource(R.mipmap.tab_weixin_normal);
mImgContact.setImageResource(R.mipmap.tab_address_normal);
mlmgFriend.setImageResource(R.mipmap.tab_find_frd_normal);
mImgSetting.setImageResource(R.mipmap.tab_settings_normal);
}
}
错误信息：
01-09 23:55:06.437 7131-7131/com.example.viewpagerdemo E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.viewpagerdemo, PID: 7131
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.viewpagerdemo/com.example.viewpagerdemo.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.addOnPageChangeListener(android.support.v4.view.ViewPager$OnPageChangeListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2368)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2430)
at android.app.ActivityThread.access$900(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5307)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.addOnPageChangeListener(android.support.v4.view.ViewPager$OnPageChangeListener)' on a null object reference
at com.example.viewpagerdemo.MainActivity.initEvent(MainActivity.java:56)
at com.example.viewpagerdemo.MainActivity.onCreate(MainActivity.java:42)
at android.app.Activity.performCreate(Activity.java:6865)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2321)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2430)
at android.app.ActivityThread.access$900(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5307)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699) 01-09 23:57:39.085 10770-10770/com.example.viewpagerdemo E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.viewpagerdemo, PID: 10770
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.viewpagerdemo/com.example.viewpagerdemo.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.addOnPageChangeListener(android.support.v4.view.ViewPager$OnPageChangeListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2368)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2430)
at android.app.ActivityThread.access$900(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5307)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.addOnPageChangeListener(android.support.v4.view.ViewPager$OnPageChangeListener)' on a null object reference
at com.example.viewpagerdemo.MainActivity.initEvent(MainActivity.java:56)
at com.example.viewpagerdemo.MainActivity.onCreate(MainActivity.java:42)
at android.app.Activity.performCreate(Activity.java:6865)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2321)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2430)
at android.app.ActivityThread.access$900(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5307)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
请输入代码好神奇，第二天重新打开电脑，重新运行，就没这个问题.....
把XML也贴一下