android: getFragmentManager() 返回 null

Question

编辑:问题是 fragment 正从 Activity 中分离出来。但是，我不知道如何防止这种情况。

我有一个使用标签栏的应用程序。单击其中一个选项卡时，它会在选项卡栏下方的空间中加载一个主题列表。其中一个主题是“方向”。单击此按钮后，空间现在将替换为顶部有另一个栏(标签栏下方)的布局，其中包括“后退”按钮和“获取路线”按钮。该栏下方是该位置的谷歌地图。如果我单击“返回”，我将按预期返回到列表。然后，如果我单击列表中的“方向”，我会按预期返回 map 。然后，如果我再次单击“返回”而不是再次将我返回到列表，它会使应用程序崩溃。它显示了指向后退按钮的 setOnClickListener 内的 FragmentTransaction ft = getFragmentManager().beginTransaction(); 行的 NullPointerException。不确定为什么它会失去对 fragmentManager 的跟踪。

这是最初加载列表的选项卡文件:

package org.childrensmuseum.visittcmindy;

import java.util.ArrayList;

import android.content.Context;
import android.graphics.drawable.GradientDrawable;
import android.graphics.drawable.GradientDrawable.Orientation;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

public class InfoTab extends Fragment {
    private ArrayList<InfoPage> pages;
    private TCMSQLiteHelper sqliteHelper;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        sqliteHelper = new TCMSQLiteHelper(this.getActivity());
        pages = sqliteHelper.getAllPages();
        InfoPage directions = new InfoPage();
        directions.setPage_id(101);
        directions.setTitle("Directions");
        InfoPage calendar = new InfoPage();
        calendar.setPage_id(102);
        calendar.setTitle("Calendar");
        pages.add(1, directions);
        pages.add(2, calendar);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.infolist, container, false);
        ListView infoList = (ListView)v.findViewById(R.id.infolistview);
        int[] colors = {0xFFCFE8FF,0xFFCFE8FF};
        infoList.setDivider(new GradientDrawable(Orientation.RIGHT_LEFT, colors));
        infoList.setDividerHeight(2);

        ArrayList<String> valueList = new ArrayList<String>();
        for(InfoPage page : pages){
            valueList.add(page.getTitle());
        }
        String[] values = new String[valueList.size()];
        values = valueList.toArray(values);

        infoList.setAdapter(new InfoAdapter(getActivity(), values));

        infoList.setOnItemClickListener(new OnItemClickListener(){

            @Override
            public void onItemClick(AdapterView<?> parent, View v, int p,
                    long id) {
                long page_id = pages.get(p).getPage_id();
                // If Directions
                if(page_id==101){
                    DirectionsView directions = new DirectionsView();
                    FragmentTransaction ft = getFragmentManager().beginTransaction();
                    ft.replace(R.id.realtabcontent, directions);
                    ft.commit();
                } else {
                    PageDetails details = PageDetails.newInstance(pages.get(p).getPage_id()); 
                    FragmentTransaction ft = getFragmentManager().beginTransaction();
                    ft.replace(R.id.realtabcontent, details);
                    ft.commit();
                }

            }

        });
        return v;
    }

    private class InfoAdapter extends ArrayAdapter<String> {

        public InfoAdapter(Context context, String[] values) {
            super(context, R.layout.explorecell, values);
            // TODO Auto-generated constructor stub
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            LayoutInflater inflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View row = inflater.inflate(R.layout.infocell,parent,false);

            InfoPage page = pages.get(position);

            if(position % 2 != 0){
                row.setBackgroundColor(getResources().getColor(R.color.listblue));
            } else {
                row.setBackgroundColor(getResources().getColor(R.color.white));
            }

            String page_icon = "page_" + page.getPage_id();
            ImageView iv = (ImageView)row.findViewById(R.id.infoImage);
            TextView tv = (TextView)row.findViewById(R.id.infoText);

            String title = page.getTitle();

            String[] titleParts = title.split("[ ]");
            String newTitle = "";
            for(int i=0;i<titleParts.length;i++){
                titleParts[i] = titleParts[i].substring(0,1).toUpperCase() + titleParts[i].substring(1);
                newTitle += titleParts[i];
                if(i<titleParts.length-1){
                    newTitle += " ";
                }
            }

            iv.setImageResource(getActivity().getResources().getIdentifier(page_icon, "drawable","org.childrensmuseum.visittcmindy"));
            tv.setText(newTitle);
            return row;
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if(sqliteHelper != null) {
            sqliteHelper.close();
        }
    }

}

这是当您单击列表中的项目时调用的 DirectionsView 的文件:

package org.childrensmuseum.visittcmindy;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.List;

import android.app.Dialog;
import android.content.Intent;
import android.location.Address;
import android.location.Geocoder;
import android.location.Location;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.util.Log;
import android.view.InflateException;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesClient;
import com.google.android.gms.location.LocationClient;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

public class DirectionsView extends Fragment implements 
GooglePlayServicesClient.ConnectionCallbacks, 
GooglePlayServicesClient.OnConnectionFailedListener {
    private static View v;
    private MainApplication main;
    private LocationClient mLocationClient;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        main = MainApplication.getInstance();
        mLocationClient = new LocationClient(getActivity(), this, this);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        if(v != null){
            ViewGroup parent = (ViewGroup) v.getParent();
            if(parent != null){
                parent.removeView(v);
            }
        }
        try {
            mLocationClient.connect();
            v = inflater.inflate(R.layout.directions, container, false);
            GoogleMap mMap;
            mMap = ((SupportMapFragment) getFragmentManager().findFragmentById(R.id.directionsmap)).getMap();
            Geocoder coder = new Geocoder(getActivity());
            List<Address> address;

            try {
                Log.d("DEBUG","2");
                String museumAddress = "The Children's Museum of Indianapolis, 3000 North Meridian St, Indianapolis, IN 46208";
                address = coder.getFromLocationName(museumAddress, 1);
                Address museumLocation = address.get(0);
                mMap.addMarker(new MarkerOptions()
                        .position(new LatLng(museumLocation.getLatitude(), museumLocation.getLongitude()))
                        .title(getResources().getString(R.string.museumTitle)));
            } catch(Exception e) {
                Log.d("DEBUG","Error Adding Marker: "+e.getLocalizedMessage());
            }
            Button backButton = (Button)v.findViewById(R.id.backtoexhibits);
            backButton.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View v) {
                    FragmentTransaction ft = getFragmentManager().beginTransaction();
                    InfoTab infoTab = new InfoTab();
                    ft.replace(R.id.realtabcontent, infoTab);
                    ft.commit();
                }
            });

            Button directionsButton = (Button)v.findViewById(R.id.getdirections);
            directionsButton.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    try {
                        openDirectionsDialog();
                    } catch (UnsupportedEncodingException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            });
        } catch (InflateException e){
            /* map is already there, just return view as it is */
            e.printStackTrace();
        }

        return v;
    }

    @Override
    public void onConnectionFailed(ConnectionResult result) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onConnected(Bundle connectionHint) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onDisconnected() {
        // TODO Auto-generated method stub

    }

    private void openDirectionsDialog() throws UnsupportedEncodingException{
        final Dialog dialog = new Dialog(getActivity());
        dialog.setContentView(R.layout.getdirections);
        dialog.setTitle("Get Directions");
        Button useAddressBtn = (Button)dialog.findViewById(R.id.useAddress);
        Button useLocationBtn = (Button)dialog.findViewById(R.id.useLocationBtn);
        final EditText addressText = (EditText)dialog.findViewById(R.id.addressText);
        final String museumAddress = URLEncoder.encode("The Children's Museum of Indianapolis, 3000 North Meridian St, Indianapolis, IN 46208","UTF-8");

        useAddressBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                String address;
                try {
                    address = URLEncoder.encode(addressText.getText().toString(),"UTF-8");
                    String url = "http://maps.google.com/maps?saddr="+address+"&daddr="+museumAddress;
                    Intent intent = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(url));
                    intent.setClassName("com.google.android.apps.maps", "com.google.android.maps.MapsActivity");
                    startActivity(intent);
                } catch (UnsupportedEncodingException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

            }
        });

        useLocationBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                Location mCurrentLocation = mLocationClient.getLastLocation();
                double lat = mCurrentLocation.getLatitude();
                double lng = mCurrentLocation.getLongitude();

                String url = "http://maps.google.com/maps?saddr="+lat+","+lng+"&daddr="+museumAddress;
                Intent intent = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(url));
                intent.setClassName("com.google.android.apps.maps", "com.google.android.maps.MapsActivity");
                startActivity(intent);

            }
        });
        dialog.show();
    }

}

编辑:

这是堆栈跟踪

12-11 14:07:03.547: E/AndroidRuntime(1846): FATAL EXCEPTION: main
12-11 14:07:03.547: E/AndroidRuntime(1846): Process: org.childrensmuseum.visittcmindy, PID: 1846
12-11 14:07:03.547: E/AndroidRuntime(1846): java.lang.NullPointerException
12-11 14:07:03.547: E/AndroidRuntime(1846):     at org.childrensmuseum.visittcmindy.DirectionsView$1.onClick(DirectionsView.java:80)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at android.view.View.performClick(View.java:4424)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at android.view.View$PerformClick.run(View.java:18383)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at android.os.Handler.handleCallback(Handler.java:733)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at android.os.Handler.dispatchMessage(Handler.java:95)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at android.os.Looper.loop(Looper.java:137)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at android.app.ActivityThread.main(ActivityThread.java:4998)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at java.lang.reflect.Method.invokeNative(Native Method)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at java.lang.reflect.Method.invoke(Method.java:515)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
12-11 14:07:03.547: E/AndroidRuntime(1846):     at dalvik.system.NativeStart.main(Native Method)

编辑 2:

根据建议，我尝试更换

FragmentTransaction ft = getFragmentManager().beginTransaction();

与

FragmentTransaction ft = getActivity().getSupportFragmentManager().beginTransaction();

错误没有变化。

Answer 1

我推荐这个:http://developer.android.com/training/implementing-navigation/lateral.html

这是一个关于使用带导航选项卡的 viewPager 和 fragmentPagerAdapter 的教程，这样您就不必手动设置 onClickListener 来更改 fragment 。这应该可以防止 fragment 被分离。