android - getFragmentManager 返回空指针异常

Question

我的 getFragmentManager 函数 setUpMapIfNeeded() 返回空指针异常。我将 fragment 与 activity_main.xml 分开放置，这里是我的代码:

activity_main.xml :

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.yai.testmap.MainActivity"
tools:ignore="MergeRootFrame" /> 

已更新

fragment _main.xml:

<?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">

<!--  MapView-->

<com.google.android.gms.maps.MapView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/map"
 />

这是我的 *.java 文件:

已更新

package com.yai.testmap;import android.support.v7.app.ActionBarActivity;import android.support.v4.app.Fragment;import android.os.Bundle;import android.view.LayoutInflater;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.ViewGroup;/* FOR ERROR REPPORT */import android.util.Log;/* IMPORT FOR DROPDOWNLIST USED THIS PROJECT */import android.widget.CheckBox;import android.widget.Spinner;import android.widget.Toast;import android.widget.AdapterView;import android.widget.ArrayAdapter;import android.widget.AdapterView.OnItemSelectedListener;import com.google.android.gms.common.ConnectionResult;import com.google.android.gms.common.GooglePlayServicesNotAvailableException;import com.google.android.gms.common.GooglePlayServicesUtil;/* IMPORT FOR GOOGLE MAP */import com.google.android.gms.maps.GoogleMap;import com.google.android.gms.maps.MapFragment;import com.google.android.gms.maps.MapsInitializer;import com.google.android.gms.maps.SupportMapFragment;import com.google.android.gms.maps.MapView;/* FOR GOOGLE MAP TYPE */import static com.google.android.gms.maps.GoogleMap.MAP_TYPE_HYBRID;import static com.google.android.gms.maps.GoogleMap.MAP_TYPE_NONE;import static com.google.android.gms.maps.GoogleMap.MAP_TYPE_NORMAL;import static com.google.android.gms.maps.GoogleMap.MAP_TYPE_SATELLITE;import static com.google.android.gms.maps.GoogleMap.MAP_TYPE_TERRAIN;public class MainActivity extends ActionBarActivity implements OnItemSelectedListener {    private static MapView mMapView;    private static MapFragment mMapFragment;    private static GoogleMap mGoogleMap;    private static CheckBox mTrafficCheckbox, mLocationCheckbox, mBuildingCheckbox, mIndoorCheckbox;    public static class PlaceholderFragment extends Fragment {        public PlaceholderFragment() {        }        @Override        public View onCreateView(LayoutInflater inflater, ViewGroup container,                Bundle savedInstanceState) {            View rootView = inflater.inflate(R.layout.fragment_main, container,                    false);            Spinner spinner = (Spinner) rootView.findViewById(R.id.spinnerOption);            ArrayAdapter adapter = ArrayAdapter.createFromResource(getActivity(), R.array.spinner_option_string, android.R.layout.simple_spinner_item);            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);            spinner.setAdapter(adapter);            spinner.setOnItemSelectedListener((OnItemSelectedListener) getActivity());            mTrafficCheckbox = (CheckBox) rootView.findViewById(R.id.checkbox_traffic);            mLocationCheckbox = (CheckBox) rootView.findViewById(R.id.checkbox_location);            mBuildingCheckbox = (CheckBox) rootView.findViewById(R.id.checkbox_building);            mIndoorCheckbox = (CheckBox) rootView.findViewById(R.id.checkbox_indoor);            MapsInitializer.initialize(getActivity());            switch (GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity()) )            {            case ConnectionResult.SUCCESS :                mMapView = (MapView) rootView.findViewById(R.id.map);                   mMapView.onCreate(savedInstanceState);                if(mMapView != null){                    mGoogleMap = mMapView.getMap();                    mGoogleMap.getUiSettings().setMyLocationButtonEnabled(false);                    mGoogleMap.setMyLocationEnabled(true);                }            }               return rootView;        }    }    @Override    protected void onCreate(Bundle savedInstanceState) {            super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        if (savedInstanceState == null) {            getSupportFragmentManager().beginTransaction()                    .add(R.id.container, new PlaceholderFragment()).commit();        }               setUpMapIfNeeded();             }       private void setUpMapIfNeeded(){        if(mGoogleMap == null){                 //mMapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);            mGoogleMap = mMapView.getMap();        }    }    private boolean checkReady(){        if(mGoogleMap == null){            Toast.makeText(this, R.string.map_not_ready, Toast.LENGTH_SHORT).show();            return false;        }        return true;    }    private void updateTraffic(){        if(!checkReady()){            return;        }        mGoogleMap.setTrafficEnabled(mTrafficCheckbox.isChecked());    }    public void onTrafficToggled(View view){        updateTraffic();    }    private void updateLocation(){        if(!checkReady()){            return;        }        mGoogleMap.setMyLocationEnabled(mLocationCheckbox.isChecked());    }    public void onLocationToggled(View view){        updateLocation();    }    private void updateBuilding(){        if(!checkReady()){            return;        }        mGoogleMap.setBuildingsEnabled(mBuildingCheckbox.isChecked());    }    public void onBuildingToggled(View view){        updateBuilding();    }    private void updateIndoor(){        if(!checkReady()){            return;        }        mGoogleMap.setIndoorEnabled(mIndoorCheckbox.isChecked());    }    public void onIndoorToggled(View view){        updateIndoor();    }    @Override    public void onItemSelected(AdapterView parent, View view, int position, long id){         setLayer((String) parent.getItemAtPosition(position));    }    private void setLayer(String layerName){        if(!checkReady()){            return;        }        if(layerName.equals(getString(R.string.normal))){            mGoogleMap.setMapType(MAP_TYPE_NORMAL);        }        else if(layerName.equals(getString(R.string.hybrid))){            mGoogleMap.setMapType(MAP_TYPE_HYBRID);        }        else if(layerName.equals(getString(R.string.satellite))){            mGoogleMap.setMapType(MAP_TYPE_SATELLITE);        }        else if(layerName.equals(getString(R.string.terrain))){            mGoogleMap.setMapType(MAP_TYPE_TERRAIN);        }        else if(layerName.equals(getString(R.string.none_map))){            mGoogleMap.setMapType(MAP_TYPE_NONE);        }        else{            Log.i("LDA", "Error setting layer with name " + layerName);        }    }    @Override    public void onNothingSelected(AdapterView parent){    }    @Override    protected void onResume() {        super.onResume();        setUpMapIfNeeded();        if (mGoogleMap != null) {            updateTraffic();            updateLocation();            updateBuilding();            updateIndoor();        }    }       @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();        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }}

I've tried to use getSupportFramentManager with android.support.v4.app.DialogFragment support library :

mGoogleMap = ((MapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();

但还是不行。我从 eclipse Cannot cast from Fragment to MapFragment 得到了这个错误。我试图扩展到 FragmentActivity 并仍然返回空指针。但是当我尝试在函数 setUpMapIfNeeded() 中注释 getSupportFragmentManager 时，错误消失了。

这是我的 LogCat:

已更新

03-24 20:43:36.124: E/AndroidRuntime(27152): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.yai.testmap/com.yai.testmap.MainActivity}: java.lang.NullPointerException03-24 20:43:36.124: E/AndroidRuntime(27152):    at com.yai.testmap.MainActivity.setUpMapIfNeeded(MainActivity.java:104)03-24 20:43:36.124: E/AndroidRuntime(27152):    at com.yai.testmap.MainActivity.onCreate(MainActivity.java:98)

有什么想法吗？

Answer 1

转换问题可以通过以下方式解决

mGoogleMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();

如果你想在 fragment 中使用 map ，你需要使用 MapView 或者你需要扩展 SupportMapFragment。

你可以引用下面的内容

Android - android.view.InflateException: Binary XML file line #8: Error inflating class fragment