片段不切换导航抽屉

Question

我正在尝试将导航抽屉放下，我已经按照互联网上的一些教程，但他们最终都没有工作。现在我知道这很简单，但我无法理解。菜单打开，主片段加载，但如果我单击一个新片段，则无效。想法？

activity_main.xml中

<include
    layout="@layout/app_bar_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<android.support.design.widget.NavigationView
    android:id="@+id/nav_view"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:fitsSystemWindows="true"
    app:headerLayout="@layout/nav_header_main"
    app:menu="@menu/activity_main_drawer" />

MainFragment java

package com.autotools.autotools;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;



public class MainFragment extends Fragment {

public MainFragment() {


}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_main, container, false);

    // Inflate the layout for this fragment
    return rootView;
}


}

第二片段

package com.autotools.autotools;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


public class autoLoanFragment extends Fragment {

public autoLoanFragment(){

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,      Bundle savedInstanceState) {

   return inflater.inflate(R.layout.fragment_autoloan,container,false);


}

}

MainActivity java

package com.autotools.autotools;

import android.support.v4.app.FragmentManager;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    MainFragment fragment =  new MainFragment();
    android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.content_frame, fragment);
    fragmentTransaction.commit();
}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.

    int id = item.getItemId();

    if (id == R.id.nav_home) {
        MainFragment fragment =  new MainFragment();
        android.support.v4.app.FragmentTransaction fragmentTransaction =   getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.content_frame, fragment);
        fragmentTransaction.commit();
    } else if (id == R.id.nav_autoLoan) {
        autoLoanFragment fragment =  new autoLoanFragment();
        android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.content_frame, fragment);
        fragmentTransaction.commit();
    } else if (id == R.id.nav_gas) {

    } else if (id == R.id.nav_settings) {

    } else if (id == R.id.nav_share) {

    } else if (id == R.id.nav_send) {

    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}
}

Fragment_main xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">


<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Large Text"
    android:id="@+id/textView2"
    android:layout_gravity="center_horizontal|top" />
</FrameLayout>

activity_main_drawer xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

<group android:checkableBehavior="single">
    <item
        android:id="@+id/nav_home"
        android:icon="@drawable/ic_info_black_48dp"
        android:title="Home" />
    <item
        android:id="@+id/nav_autoLoan"
        android:icon="@drawable/ic_attach_money_black_48dp"
        android:title="Auto Loan Calculator" />
    <item
        android:id="@+id/nav_gas"
        android:icon="@drawable/ic_local_gas_station_black_48dp"
        android:title="Slideshow" />
    <item
        android:id="@+id/nav_settings"
        android:icon="@drawable/ic_settings_black_48dp"
        android:title="Settings" />
</group>

<item android:title="Communicate">
    <menu>
        <item
            android:id="@+id/nav_share"
            android:icon="@drawable/ic_menu_share"
            android:title="Share" />
        <item
            android:id="@+id/nav_send"
            android:icon="@drawable/ic_menu_send"
            android:title="Send" />
    </menu>
</item>

</menu>