错误：“地图片段为空”

Question

我有这个问题：错误：“Map Fragment为null”。 这是我的代码： MainActivity：

public class MainActivity extends FragmentActivity {

    ViewPager pager;
    ViewPagerAdapter adapter;
    SlidingTabLayout tabs;
    CharSequence Titles[]={"Mappa","Percorsi"};
    int Numboftabs =2;
    private GoogleMap map;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // Creating The ViewPagerAdapter and Passing Fragment Manager, Titles fot the Tabs and Number Of Tabs.
        adapter = new ViewPagerAdapter(getSupportFragmentManager(),Titles,Numboftabs);
        // Assigning ViewPager View and setting the adapter
        pager = (ViewPager) findViewById(R.id.pager);
        pager.setAdapter(adapter);
        // Assiging the Sliding Tab Layout View
        tabs = (SlidingTabLayout) findViewById(R.id.tabs);
        Integer[] iconResourceArray = {R.drawable.mapicon2, R.drawable.routeicon};
        tabs.setIconResourceArray(iconResourceArray);
        tabs.setDistributeEvenly(true); // To make the Tabs Fixed set this true, This makes the tabs Space Evenly in Available width
        // Setting Custom Color for the Scroll bar indicator of the Tab View
        tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
            @Override
            public int getIndicatorColor(int position) {
                return getResources().getColor(R.color.tabsScrollColor);
            }
        });
        // Setting the ViewPager For the SlidingTabsLayout
        tabs.setViewPager(pager);

        SupportMapFragment mapFragment = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map));
        if (mapFragment != null) {
            mapFragment.getMapAsync(new OnMapReadyCallback() {
                @Override
                public void onMapReady(GoogleMap map) {
                    loadMap(map);
                }
            });
        } else {
            Toast.makeText(this, "Error - Map Fragment was null!!", Toast.LENGTH_SHORT).show();
        }
    }

    protected void loadMap(GoogleMap googleMap) {
        map = googleMap;
        if (map != null) {
            // Map is ready
            Toast.makeText(this, "Map Fragment was loaded properly!", Toast.LENGTH_SHORT).show();
            map.setMyLocationEnabled(true);
            map.addMarker(new MarkerOptions()
                    .position(new LatLng(43.111437, 12.391310))
                    .title("Perugia"));
        } else {
            Toast.makeText(this, "Error - Map was null!!", Toast.LENGTH_SHORT).show();
        }
    }

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

然后我有两个java文件Tab1和Tab2，Tab1：

public class Tab1 extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v =inflater.inflate(R.layout.tab_1, container, false);
        return v;
    }
}

tab_1.xml和tab_2.xml，tab_1.xml：

<fragment 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:id="@+id/map"
    tools:context=".MainActivity"
    android:name="com.google.android.gms.maps.SupportMapFragment" />

这是activity_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="wrap_content"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <samples.exoguru.Parchiamo.SlidingTabLayout
        android:id="@+id/tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:elevation="2dp"
        android:background="@color/ColorPrimary"/>

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:layout_weight="1" />

</LinearLayout>

ViewPagerAdapter：

public class ViewPagerAdapter extends FragmentStatePagerAdapter {

    CharSequence Titles[]; // This will Store the Titles of the Tabs which are Going to be passed when ViewPagerAdapter is created
    int NumbOfTabs; // Store the number of tabs, this will also be passed when the ViewPagerAdapter is created

    // Build a Constructor and assign the passed Values to appropriate values in the class
    public ViewPagerAdapter(FragmentManager fm,CharSequence mTitles[], int mNumbOfTabsumb) {
        super(fm);

        this.Titles = mTitles;
        this.NumbOfTabs = mNumbOfTabsumb;
    }

    //This method return the fragment for the every position in the View Pager
    @Override
    public Fragment getItem(int position) {
        if(position == 0) // if the position is 0 we are returning the First tab
        {
            Tab1 tab1 = new Tab1();
            return tab1;
        }
        else             // As we are having 2 tabs if the position is now 0 it must be 1 so we are returning second tab
        {
            Tab2 tab2 = new Tab2();
            return tab2;
        }
    }

    // This method return the titles for the Tabs in the Tab Strip
    @Override
    public CharSequence getPageTitle(int position) {
        return Titles[position];
    }

    // This method return the Number of tabs for the tabs Strip
    @Override
    public int getCount() {
        return NumbOfTabs;
    }
}

这是解决方案：

mSupportMapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);
    if (mSupportMapFragment == null) {
        FragmentManager fragmentManager = getFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        mSupportMapFragment = SupportMapFragment.newInstance();
        fragmentTransaction.replace(R.id.map, mSupportMapFragment).commit();
    }

    if (mSupportMapFragment != null) {
        mSupportMapFragment.getMapAsync(new OnMapReadyCallback() {
            @Override
            public void onMapReady(final GoogleMap googleMap) {
                if (googleMap != null) {