android 1.4 用创建Blank Activity （ use a fragment ）建立两个fra

package com.jikexueyuan.myapplication;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
public class MainActivity extends AppCompatActivity  {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity">
    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />
    </android.support.design.widget.AppBarLayout>
    <include layout="@layout/content_main" />
</android.support.design.widget.CoordinatorLayout>

content_main.xml

<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto" android:id="@+id/fragment"
android:name="com.jikexueyuan.myapplication.MainActivityFragment"
android:layout_width="match_parent" android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:layout="@layout/fragment_main" />

AnotherFragment

package com.jikexueyuan.myapplication;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
 * A placeholder fragment containing a simple view.
 */
public class MainActivityFragment extends Fragment {
    public MainActivityFragment() {
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        rootView.findViewById(R.id.btnShowAnotherFragment).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                      getFragmentManager().beginTransaction().replace(R.id.fragment,new AnotherFragment()).commit();
            }
        });
        return rootView;
    }
}

fragment_main.xml

<LinearLayout 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" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:showIn="@layout/activity_main"
    tools:context=".MainActivityFragment">
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="呈现另一个Fragment"
        android:id="@+id/btnShowAnotherFragment"/>
</LinearLayout>

AnotherFragment

package com.jikexueyuan.myapplication;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
 * Created by Administrator on 2015/11/22 0022.
 */
public class AnotherFragment extends Fragment {
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View root = inflater.inflate(R.layout.another_fragment,container,false);
        return root;
    }
}

another_fragment.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="这是另一个Fragment"
        android:id="@+id/textView" />
</LinearLayout>

启动App

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问题是，本人需要在新的页面显示另一个fragment，为什么会在一个页面。求怎么样解决？