The application's PagerAdapter changed the adapter's contents without calling PagerAdapter#notifyDat

参考

8、在初始化ViewPager时，应先给Adapter初始化内容后再将该adapter传给ViewPager，如果不这样处理，在更新adapter的内容后，应该调用一下adapter的notifyDataSetChanged方法，否则在ADT22以上使用会报The application's PagerAdapter changed the adapter's contents without calling PagerAdapter#notifyDataSetChanged的异常，具体原因可参考：http://stackoverflow.com/questions/16756131/fragmentstatepageradapter-stopped-working-after-updating-to-adt-22

问题

使用viewpager及fragment的代码如下：
test_tab1.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:orientation="vertical"              android:layout_width="match_parent"              android:layout_height="match_parent">    <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/main_tabs" android:orientation="vertical">        <android.support.v4.view.ViewPager android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/viewpager">        </android.support.v4.view.ViewPager>    </LinearLayout>    <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="horizontal">        <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btn_tab_1" android:text="tab 1"/>        <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btn_tab_2" android:text="tab 2"/>        <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btn_tab_3" android:text="tab 3"/>        <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btn_tab_4" android:text="tab 4"/>    </LinearLayout></LinearLayout>

四个fragment的layout如下：
fragment_1.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:orientation="vertical"              android:layout_width="match_parent"              android:layout_height="match_parent"><TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="这是标签1"/></LinearLayout>

fragment_2.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:orientation="vertical"              android:layout_width="match_parent"              android:layout_height="match_parent"><TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="这是标签2"/></LinearLayout>

fragment_3.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:orientation="vertical"              android:layout_width="match_parent"              android:layout_height="match_parent"><TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="这是标签3"/></LinearLayout>

fragment_4.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:orientation="vertical"              android:layout_width="match_parent"              android:layout_height="match_parent"><TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="这是标签4"/></LinearLayout>

四个fragment类：
fragment_1.java

package com.app.activities;        import android.os.Bundle;        import android.support.v4.app.Fragment;        import android.view.LayoutInflater;        import android.view.View;        import android.view.ViewGroup;public class fragment_1 extends Fragment{    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)    {        return  inflater.inflate(R.layout.fragment_1, container, false);    }}

fragment_2.java

package com.app.activities;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;public class fragment_2 extends Fragment{    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)    {        return  inflater.inflate(R.layout.fragment_2, container, false);    }}

fragment_3.java

package com.app.activities;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;public class fragment_3 extends Fragment{    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)    {        return  inflater.inflate(R.layout.fragment_3, container, false);    }}

fragment_4.java

package com.app.activities;import android.os.Bundle;import android.support.v4.app.Fragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;public class fragment_4 extends Fragment{    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)    {        return  inflater.inflate(R.layout.fragment_4, container, false);    }}

运行结果如下：

解释

出现这个问题的最基本原因是因为初始化adapter的时候，已经将fragments的数量定死了，在后面将fragment添加上去的话，需要通知adapter数据变更了；
第二种解决方案是先将fragments都添加完毕再初始化adapter，即两种方案为：
方案1：

package com.app.activities;import android.os.Bundle;import android.support.v4.app.Fragment;import android.support.v4.app.FragmentPagerAdapter;import android.support.v4.view.ViewPager;import android.support.v7.app.ActionBarActivity;import android.util.Log;import android.widget.Button;import java.util.ArrayList;/** * Created by Administrator on 2015/8/28. */public class test_tab1 extends ActionBarActivity {    private ViewPager viewPager;    private Button btn_tab1;    private Button btn_tab2;    private Button btn_tab3;    private Button btn_tab4;    private FragmentPagerAdapter pagerAdapter;    private ArrayList<Fragment> fragments=new ArrayList<Fragment>();    private void initUI(){        viewPager=(ViewPager)findViewById(R.id.viewpager);        btn_tab1=(Button)findViewById(R.id.btn_tab_1);        btn_tab2=(Button)findViewById(R.id.btn_tab_2);        btn_tab3=(Button)findViewById(R.id.btn_tab_3);        btn_tab4=(Button)findViewById(R.id.btn_tab_4);        pagerAdapter=new FragmentPagerAdapter(getSupportFragmentManager()) {            @Override            public Fragment getItem(int position) {                return fragments.get(position);            }            @Override            public int getCount() {                return fragments.size();            }        };        viewPager.setAdapter(pagerAdapter);        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {            @Override            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {                Log.e("TAG-",""+position);            }            @Override            public void onPageSelected(int position) {            }            @Override            public void onPageScrollStateChanged(int state) {            }        });        fragment_1 tab1=new fragment_1();        fragment_2 tab2=new fragment_2();        fragment_3 tab3=new fragment_3();        fragment_4 tab4=new fragment_4();        fragments.add(tab1);        fragments.add(tab2);        fragments.add(tab3);        fragments.add(tab4);        pagerAdapter.notifyDataSetChanged();    }    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.test_tab1);        initUI();    }}

方案2：

package com.app.activities;import android.os.Bundle;import android.support.v4.app.Fragment;import android.support.v4.app.FragmentPagerAdapter;import android.support.v4.view.ViewPager;import android.support.v7.app.ActionBarActivity;import android.util.Log;import android.widget.Button;import java.util.ArrayList;/** * Created by Administrator on 2015/8/28. */public class test_tab1 extends ActionBarActivity {    private ViewPager viewPager;    private Button btn_tab1;    private Button btn_tab2;    private Button btn_tab3;    private Button btn_tab4;    private FragmentPagerAdapter pagerAdapter;    private ArrayList<Fragment> fragments=new ArrayList<Fragment>();    private void initUI(){        viewPager=(ViewPager)findViewById(R.id.viewpager);        btn_tab1=(Button)findViewById(R.id.btn_tab_1);        btn_tab2=(Button)findViewById(R.id.btn_tab_2);        btn_tab3=(Button)findViewById(R.id.btn_tab_3);        btn_tab4=(Button)findViewById(R.id.btn_tab_4);        fragment_1 tab1=new fragment_1();        fragment_2 tab2=new fragment_2();        fragment_3 tab3=new fragment_3();        fragment_4 tab4=new fragment_4();        fragments.add(tab1);        fragments.add(tab2);        fragments.add(tab3);        fragments.add(tab4);                pagerAdapter=new FragmentPagerAdapter(getSupportFragmentManager()) {            @Override            public Fragment getItem(int position) {                return fragments.get(position);            }            @Override            public int getCount() {                return fragments.size();            }        };        viewPager.setAdapter(pagerAdapter);        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {            @Override            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {                Log.e("TAG-",""+position);            }            @Override            public void onPageSelected(int position) {            }            @Override            public void onPageScrollStateChanged(int state) {            }        });    }    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.test_tab1);        initUI();    }}