ViewPager+FragmentTabhost 解决办法

来源：互联网发布：java ee 新闻策划案例编辑：程序博客网时间：2024/06/01 08:48

android viewpager+fragmentTabhost：直接将一个FragmentTabhost 加入到viewPager中，滑动viewPager再次返回之前FragmentTabhost
会出现java.lang.NullPointerException, 是在FragmentState.instantiate 出错。

第一次加载viewPager不会出错，第二次就会出现以上情况，解决办法如下代码：
注：TabsInfo是关键，在getItem方法中需要使用Fragment.instantiate得到一个Fragment

经测试ViewPager + fragment 不会出现以上所说情况，可以在构造的时候传递一个

ArrayList<Fragmet> list,再通过getItem 返回即可，有不正确的地方还请指正...

[1].[图片] 0815_16_24_01.png 跳至 [1] [2]

[2].[代码] [Java]代码跳至 [1] [2]

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importjava.util.ArrayList;
importandroid.content.Context;
importandroid.os.Bundle;
importandroid.support.v4.app.Fragment;
importandroid.support.v4.app.FragmentActivity;
importandroid.support.v4.app.FragmentStatePagerAdapter;
 
 
//************************自定义pagerAdapter**********************
publicclass MviewPagerAdapter extendsFragmentStatePagerAdapter{
     
    privatefinal ArrayList<TabsInfo> lstTabsInfo;
    privatefinal Context mContext;
    publicstatic class TabsInfo {
        privatefinal Class<?> clss_;
        privatefinal Bundle args_;
        publicTabsInfo(Class<?> clss, Bundle args) {
            this.clss_ = clss;
            this.args_ = args;
        }
    }
    publicMviewPagerAdapter(FragmentActivity activity, ArrayList<TabsInfo> lstTabsInfo) {
        super(activity.getSupportFragmentManager());
        mContext = activity;
        this.lstTabsInfo = lstTabsInfo;
    }
 
    @Override
    publicFragment getItem(intposition) {
        // TODO Auto-generated method stub
        TabsInfo info = lstTabsInfo.get(position);
        returnFragment.instantiate(mContext, info.clss_.getName(), info.args_);
    }
 
    @Override
    publicint getCount() {
        // TODO Auto-generated method stub
        returnlstTabsInfo.size();
    }
}
 
//*******************应用************************
publicclass MainActivity extendsFragmentActivity implementsOnPageChangeListener, OnCheckedChangeListener{
    privateRadioGroup mRadioGroup;
    privateViewPager mViewPager;
    privateArrayList<Integer> lstCheckIds;
    privateArrayList<TabsInfo> lstTabsInfos;
    @Override
    protectedvoid onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mRadioGroup = (RadioGroup)findViewById(R.id.radiogroup);
        mRadioGroup.check(R.id.chengzai);
        lstCheckIds = newArrayList<Integer>();
        for(inti=0; i<5; i++) {
            lstCheckIds.add(R.id.chengzai+i);
        }
        mRadioGroup.setOnCheckedChangeListener(this);
        mViewPager = (ViewPager)findViewById(R.id.main_viewPager);
        lstTabsInfos = newArrayList<TabsInfo>();
        //**********此处为关键代码*************
        lstTabsInfos.add(newTabsInfo(FireDisasterFragment.class,null));
        lstTabsInfos.add(newTabsInfo(SuperviseFragment.class,null));
        lstTabsInfos.add(newTabsInfo(Tab1.class,null));
        lstTabsInfos.add(newTabsInfo(Tab2.class,null));
        lstTabsInfos.add(newTabsInfo(Tab1.class,null));
        MviewPagerAdapter adapter = newMviewPagerAdapter(this, lstTabsInfos);
        mViewPager.setAdapter(adapter);
        mViewPager.setCurrentItem(0);
        mViewPager.setOnPageChangeListener(this);
    }
     
    @Override
    publicvoid onCheckedChanged(RadioGroup group, intcheckedId) {
        // TODO Auto-generated method stub
        for(inti=0; i<lstCheckIds.size(); i++) {
            if(lstCheckIds.get(i) == checkedId) {
                mViewPager.setCurrentItem(i);
                break;
            }
        }
    }
     
    @Override
    publicvoid onPageScrollStateChanged(intarg0) {
        // TODO Auto-generated method stub
         
    }
     
    @Override
    publicvoid onPageScrolled(intarg0, floatarg1, intarg2) {
        // TODO Auto-generated method stub
         
    }
     
    @Override
    publicvoid onPageSelected(intposition) {
        // TODO Auto-generated method stub
        mRadioGroup.check(lstCheckIds.get(position));
    }
 
}
 
//*********另附上 FireDisasterFragment(FragmentTabhost)关键代码**************
@Override
    publicView onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        Log.e("fire_oncreateview","oncreateview");
         
        View view = (View)inflater.inflate(R.layout.firedisaste_layout, container, false);
        mTabHost = (FragmentTabHost)view.findViewById(android.R.id.tabhost);
        mTabHost.setup(getActivity(), getChildFragmentManager(), R.id.realtabcontent);
        View indicator = (View)inflater.inflate(R.layout.tabwidgets_layout, null);
        TextView textView = (TextView)indicator.findViewById(R.id.tabwidget_indicator);
         
        textView.setText("tabwidget1");
        mTabHost.addTab(mTabHost.newTabSpec("tab1").setIndicator(indicator), Tab3.class,null);
         
        View indicator1 = (View)inflater.inflate(R.layout.tabwidgets_layout, null);
        TextView textView2 = (TextView)indicator1.findViewById(R.id.tabwidget_indicator);
        textView2.setText("tabwidget2");
        mTabHost.addTab(mTabHost.newTabSpec("tab2").setIndicator(indicator1), Tab4.class,null);
        returnview;
    }
 
//*********************布局代码***************************
<?xml version="1.0"encoding="utf-8"?>
<android.support.v4.app.FragmentTabHost
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/tabhost"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
 
        <TabWidget
            android:id="@android:id/tabs"
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="0"/>
 
        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:layout_weight="0"/>
 
        <FrameLayout
            android:id="@+id/realtabcontent"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"/>
 
    </LinearLayout>
</android.support.v4.app.FragmentTabHost>

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ViewPager+FragmentTabhost 解决办法

[1].[图片] 0815_16_24_01.png 跳至 [1] [2]

[2].[代码] [Java]代码 跳至 [1] [2]

[2].[代码] [Java]代码跳至 [1] [2]