<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent" >   //activity_main.xml    <FrameLayout            android:id="@+id/frame_container"    //主内容的区域        android:layout_width="match_parent"        android:layout_height="match_parent"        android:layout_above="@+id/div_view" >    </FrameLayout>    <View        android:id="@+id/div_view"        android:layout_width="fill_parent"        android:layout_height="1.0px"        android:layout_above="@+id/main_radiogroup"    //横线 在radiogroup的上面        android:layout_marginBottom="2dip"        android:background="#ffc9cacb" />    <RadioGroup        android:id="@+id/main_radiogroup"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_alignParentBottom="true" //在父布局 的下面        android:orientation="horizontal" >        <RadioButton            android:id="@+id/tab_rbo_question"            style="@style/tab_textview"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"     //占 一              android:background="@null"            android:button="@null"            android:checked="true"     // 默认选中             android:drawableTop="@drawable/selector_tab_question"    //"问他" 图片的选择器             android:text="问他"            android:textColor="@color/tv_checked_bg" />        <RadioButton            android:id="@+id/tab_rbo_message"            style="@style/tab_textview"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:background="@null"            android:button="@null"            android:drawableTop="@drawable/selector_tab_message"   // "消息" 图片选择器             android:gravity="center_horizontal"     //居中             android:text="消息" />        <RadioButton            android:id="@+id/tab_rbo_answer"            style="@style/tab_textview"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:background="@null"            android:button="@null"            android:drawableTop="@drawable/selector_tab_answer"  //"我要回答"  图片选择器器              android:gravity="center_horizontal"            android:text="我要回答" />        <RadioButton            android:id="@+id/tab_rbo_discover"            style="@style/tab_textview"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:background="@null"            android:button="@null"            android:drawableTop="@drawable/selector_tab_discover"    //"发现" 图片选择器              android:gravity="center_horizontal"            android:text="发现" />        <RadioButton            android:id="@+id/tab_rbo_user"            style="@style/tab_textview"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:background="@null"            android:button="@null"            android:drawableTop="@drawable/selector_tab_user"   //"我" 图片选择器              android:gravity="center_horizontal"            android:text="我" />    </RadioGroup></RelativeLayout>

<?xml version="1.0" encoding="utf-8"?> //selector_tab_question<selector xmlns:android="http://schemas.android.com/apk/res/android"    <item android:drawable="@drawable/tab_question_select" android:state_checked="true"></item>    <item android:drawable="@drawable/tab_question_select" android:state_pressed="true"></item>    <item android:drawable="@drawable/tab_question_nor"></item></selector>

    <style name="tab_textview">        <item name="android:textSize">11sp</item>        <item name="android:gravity">center_horizontal</item>        <item name="android:drawablePadding">2dip</item>    </style>

public class MainActivity extends FragmentActivity {    /** 底部导航 */    private RadioGroup main_radiogroup;    private Fragment mCurrent; // 当前的mCurrent    private TabFragment faxian; // 发现    private TabFragment huida; // 回答    private TabFragment denglu; // 登陆    private TabFragment xiaoxi; // 消息    private TabFragment wenta; // 问他    // private FragmentManager fm;    // private FragmentTransaction ft;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        main_radiogroup = (RadioGroup) this.findViewById(R.id.main_radiogroup);        // fm = getSupportFragmentManager();        // main_radiogroup 被选中 ,时候的监听器        main_radiogroup                .setOnCheckedChangeListener(new OnCheckedChangeListener() {                    @SuppressLint("ResourceAsColor")                    @Override                    public void onCheckedChanged(RadioGroup group, int checkedId) {                        /** 改变文字的颜色 */                        int length = group.getChildCount();                        for (int i = 0; i < length; i++) {                            RadioButton radioButton = (RadioButton) group                                    .getChildAt(i);                            if (radioButton.getId() != checkedId) {                                // 没有选中的 时候的文字颜色                                radioButton.setTextColor(getResources()                                        .getColor(R.color.tv_checked_nor));                            } else { // 选中的时候的文字颜色                                radioButton.setTextColor(getResources()                                        .getColor(R.color.tv_checked_bg));                            }                        }                        switch (checkedId) {                        case R.id.tab_rbo_answer:                            changeAnswer(); //切换回答                            break;                        case R.id.tab_rbo_discover:                            changeDiscover(); //切换问他                            break;                        case R.id.tab_rbo_message:                            changeMessage(); //消息                            break;                        case R.id.tab_rbo_question:                            changeQuesion();                            break;                        case R.id.tab_rbo_user:  //用户                            changeUser();                            break;                        }                    }                });
　　      mCurrent = new TabFragment(); //起始时候 给个值 ,不然会 报异常
        /** 默认选择第一个 */        changeQuesion();       }    /**     * 切换问他     */    private void changeQuesion() {        if (wenta == null) {            wenta = new TabFragment();            Bundle bundle = new Bundle();            bundle.putString("name", "问他");            wenta.setArguments(bundle);        }        switchContent(wenta);        // ft.replace(R.id.frame_container, tab1);        // ft.commit();    }    /**     * 切换消息     */    private void changeMessage() {        if (xiaoxi == null) {            xiaoxi = new TabFragment();            Bundle bundle = new Bundle();            bundle.putString("name", "消息");            xiaoxi.setArguments(bundle);        }        switchContent(xiaoxi);        // ft.replace(R.id.frame_container, tab1);        // ft.commit();    }    /***     * 切换登录     */    private void changeUser() {        if (denglu == null) {            denglu = new TabFragment();            Bundle bundle = new Bundle();            bundle.putString("name", "用户");            denglu.setArguments(bundle);        }        switchContent(denglu);        // ft.replace(R.id.frame_container, tab1);        // ft.commit();    }    /***     * 切换回答     */    private void changeAnswer() {        if (huida == null) {            huida = new TabFragment();            Bundle bundle = new Bundle();            bundle.putString("name", "回答");            huida.setArguments(bundle);        }        switchContent(huida);        // ft.replace(R.id.frame_container, tab1);        // ft.commit();    }    /***     * 切换发现     */    private void changeDiscover() {        if (faxian == null) {            faxian = new TabFragment();            Bundle bundle = new Bundle();            bundle.putString("name", "发现");            faxian.setArguments(bundle);        }        switchContent(faxian);        // ft.replace(R.id.frame_container, tab1);        // ft.commit();    }    /** 修改显示的内容 不会重新加载 **/    public void switchContent(Fragment to) {        if (mCurrent != to) {            FragmentTransaction transaction = getSupportFragmentManager()                    .beginTransaction();            if (!to.isAdded()) { // 先判断是否被add过                transaction.hide(mCurrent).add(R.id.frame_container, to)                        .commit(); // 隐藏当前的fragment，add下一个到Activity中            } else {                transaction.hide(mCurrent).show(to).commit(); // 隐藏当前的fragment，显示下一个            }            mCurrent = to;        }        // showContent();    }}

public class TabFragment extends Fragment {    private String tab_name;    @Override    public void onAttach(Activity activity) {        super.onAttach(activity);        //得到 activity 传来的 值        tab_name=getArguments().getString("name");            }        @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,            Bundle savedInstanceState) {        View view=inflater.inflate(R.layout.fragment_tab, container, false);        TextView tv=(TextView) view.findViewById(R.id.textview1);        tv.setText(tab_name);        return view;    }}

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical" >  //fragment_tab        <TextView        android:id="@+id/textview1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:textSize="100sp"        android:layout_centerInParent="true"   // 居 父中间        /></RelativeLayout>