java - getMap() 方法可能返回 null？

Question

我使用处理程序从支持 map fragment 中获取 GoogleMap。我真的迷路了，几天来一直在努力修复它。 map 加载正常，但我怀疑它返回的是空值。我知道可能有一些不好的做法，但这不是我的问题。我尝试使用 AsyncTask 和 Handler。我在各种移动设备上测试过，没有使用模拟器。这是我的代码，我删除了一些其他导入，但它们在那里(显然不是整个程序):

import com.codexmalta.mytravelbuddy.R;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;

import android.support.v4.app.FragmentActivity;  
import com.google.android.gms.maps.SupportMapFragment;  

import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

public class Itinerary extends FragmentActivity implements View.OnClickListener {

    //Google Map
    GoogleMap map;

    byte choice;

    protected ProgressDialog dialog;

    CameraPosition cameraPosition;

    Timer timer = new Timer();

    LinearLayout[] l = new LinearLayout[10];
    TextView[] time = new TextView[10];
    TextView[] desc = new TextView[10];
    TextView[] loc = new TextView[10];
    double[] lat = new double[10];
    double[] lng = new double[10];

    MarkerOptions[] marker = new MarkerOptions[10];
    //Get Itinerary
    GetItinerary gi = new GetItinerary();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_starting_point);   
        choice = getIntent().getByteExtra("choice", choice);


        //Methods
        getMapFragment();

        getLayouts();
        getFields();
        gi.main(choice);
        fillFields();
        removeExtraLayouts(gi.giveNumDay1(),gi.giveNumDay2());
        getMap();
        displayMarkers();
        animateCamera();



    }


SupportMapFragment fm = new SupportMapFragment();



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

    private void removeExtraMarkers(){
        for(int i = 0; i < 10; i++){
            if(lat[i] == 0 && lng[i] == 0){
                marker[i].alpha(0);
                }
        }
    }

    private void displayMarkers(){
        String[] s = new String[10];
        for(int i = 0; i < 10; i++){
            s[i] = (String) loc[i].getText();
            map.addMarker(marker[i].position(new LatLng(lat[i], lng[1])).title(s[i])).setVisible(true); 
        }
    }

    public void getMapFragment(){
        fm = (SupportMapFragment)   getSupportFragmentManager().findFragmentById(R.id.map);
    }


    Handler mHandler = new Handler();
    public void getMap(){   

        mHandler.post(new Runnable() {  
                    @Override
                    public void run() {
                        GoogleMap map = fm.getMap();
                        if (map != null) {
                            map.setMyLocationEnabled(true);
                            // INIT HERE
                            map.getUiSettings().setMyLocationButtonEnabled(false);
                            // ...

                        } else mHandler.post(this);
                    }
                });

        while(map == null){
        map = fm.getMap();  
        if(map!= null)break;
        }
        }

    private void removeExtraLayouts(int a, int b){

        //Day One

        switch(a){
        case 5:
            l[0].removeAllViews();
            l[1].removeAllViews();
            l[2].removeAllViews();
            l[3].removeAllViews();
            l[4].removeAllViews();
            break;
        case 4:
            l[1].removeAllViews();
            l[2].removeAllViews();
            l[3].removeAllViews();
            l[4].removeAllViews();
            break;
        case 3:
            l[2].removeAllViews();
            l[3].removeAllViews();
            l[4].removeAllViews();
            break;
        case 2:
            l[3].removeAllViews();
            l[4].removeAllViews();
            break;
        case 1:
            l[4].removeAllViews();
            break;

        }

        //Day Two

        switch(b){
        case 5:
            l[5].removeAllViews();
            l[6].removeAllViews();
            l[7].removeAllViews();
            l[8].removeAllViews();
            l[9].removeAllViews();
            break;
        case 4:
            l[6].removeAllViews();
            l[7].removeAllViews();
            l[8].removeAllViews();
            l[9].removeAllViews();
            break;
        case 3:
            l[7].removeAllViews();
            l[8].removeAllViews();
            l[9].removeAllViews();
            break;
        case 2:
            l[8].removeAllViews();
            l[9].removeAllViews();
            break;
        case 1:
            l[9].removeAllViews();
            break;
        }

    }

    private void getLayouts(){
        l[0] = (LinearLayout)findViewById(R.id.a1);
        l[0].setOnClickListener(this);
        l[1] = (LinearLayout)findViewById(R.id.a2);
        l[1].setOnClickListener(this);
        l[2] = (LinearLayout)findViewById(R.id.a3);
        l[2].setOnClickListener(this);
        l[3] = (LinearLayout)findViewById(R.id.a4);
        l[3].setOnClickListener(this);
        l[4] = (LinearLayout)findViewById(R.id.a5);
        l[4].setOnClickListener(this);
        l[5] = (LinearLayout)findViewById(R.id.a6);
        l[5].setOnClickListener(this);
        l[6] = (LinearLayout)findViewById(R.id.a7);
        l[6].setOnClickListener(this);
        l[7] = (LinearLayout)findViewById(R.id.a8); 
        l[7].setOnClickListener(this);
        l[8] = (LinearLayout)findViewById(R.id.a9);
        l[8].setOnClickListener(this);
        l[9] = (LinearLayout)findViewById(R.id.a10);
        l[9].setOnClickListener(this);
    }

    private void getFields(){
        time[0] = (TextView)findViewById(R.id.time1);
        desc[0] = (TextView)findViewById(R.id.desc1);
        loc[0] = (TextView)findViewById(R.id.loc1);

        time[1] = (TextView)findViewById(R.id.time2);
        desc[1] = (TextView)findViewById(R.id.desc2);
        loc[1] = (TextView)findViewById(R.id.loc2);

        time[2] = (TextView)findViewById(R.id.time3);
        desc[2] = (TextView)findViewById(R.id.desc3);
        loc[2] = (TextView)findViewById(R.id.loc3);

        time[3] = (TextView)findViewById(R.id.time4);
        desc[3] = (TextView)findViewById(R.id.desc4);
        loc[3] = (TextView)findViewById(R.id.loc4);

        time[4] = (TextView)findViewById(R.id.time5);
        desc[4] = (TextView)findViewById(R.id.desc5);
        loc[4] = (TextView)findViewById(R.id.loc5);

        time[5] = (TextView)findViewById(R.id.time6);
        desc[5] = (TextView)findViewById(R.id.desc6);
        loc[5] = (TextView)findViewById(R.id.loc6);

        time[6] = (TextView)findViewById(R.id.time7);
        desc[6] = (TextView)findViewById(R.id.desc7);
        loc[6] = (TextView)findViewById(R.id.loc7);

        time[7] = (TextView)findViewById(R.id.time8);
        desc[7] = (TextView)findViewById(R.id.desc8);
        loc[7] = (TextView)findViewById(R.id.loc8);

        time[8] = (TextView)findViewById(R.id.time9);
        desc[8] = (TextView)findViewById(R.id.desc9);
        loc[8] = (TextView)findViewById(R.id.loc9);

        time[9] = (TextView)findViewById(R.id.time10);
        desc[9] = (TextView)findViewById(R.id.desc10);
        loc[9] = (TextView)findViewById(R.id.loc10);
    }

    private void fillFields(){
    for(int i = 0; i < 10; i++){
        time[i].setText(gi.giveTimeArray(i));
        desc[i].setText(gi.giveDescriptionArray(i));
        loc[i].setText(gi.giveLocationArray(i));
        lat[i] = gi.giveLatitudeArray(i);
        lng[i] = gi.giveLongitudeArray(i);
    }       
    }


    private void animateCamera(){
        CameraPosition.builder().target(new LatLng(20, 20)).zoom(12).build();
        map.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
    }


    @Override   
    public void onClick(View v) {
        switch(v.getId()){
        case R.id.a1:

            //animateCamera(lat[0],lng[0]);
            break;
        case R.id.a2:
            //animateCamera(lat[1],lng[1]);
            break;
        case R.id.a3:
            //animateCamera(lat[2],lng[2]);
            break;
        case R.id.a4:
            //animateCamera(lat[3],lng[3]);
            break;
        case R.id.a5:
            //animateCamera(lat[4],lng[4]);
            break;
        case R.id.a6:
            //animateCamera(lat[5],lng[5]);
            break;
        case R.id.a7:
            //animateCamera(lat[6],lng[6]);
            break;
        case R.id.a8:
            //animateCamera(lat[7],lng[7]);
            break;
        case R.id.a9:
            //animateCamera(lat[8],lng[8]);
            break;
        case R.id.a10:
            //animateCamera(lat[9],lng[9]);
            break;
        }   
    }   
}

这是我的 list :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codexmalta.mytravelbuddy"
    android:versionCode="1"
    android:versionName="0.5" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/tb02"
        android:label="Travel Buddy"
        android:configChanges = "keyboardHidden|orientation"  
         >

        <meta-data
    android:name="com.google.android.gms.version"
    android:value="@integer/google_play_services_version" />

        <activity
            android:name="com.codexmalta.mytravelbuddy.MainActivity"
            android:label="Travel Buddy"
            android:theme="@android:style/Theme.NoTitleBar"
            android:screenOrientation="portrait" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

            </activity>


        <activity
            android:name="com.codexmalta.mytravelbuddy.Itinerary"
            android:label="Itinerary"
            android:theme="@android:style/Theme.NoTitleBar" 
            android:screenOrientation="portrait">
        </activity>
    <meta-data
    android:name="com.google.android.maps.v2.API_KEY"
    android:value="key"/>    
    </application>

    <uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
<!-- The following two permissions are not required to use
     Google Maps Android API v2, but are recommended. -->
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

    <uses-permission android:name="android.permission.INTERNET" />

    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true"/>

</manifest>

这是我在布局 xml 中保存 map 的 fragment :

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:map="http://schemas.android.com/apk/res-auto"
    android:id="@+id/RelativeLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginBottom="0dp"
    android:layout_marginEnd="0dp"
    android:layout_marginTop="-20dp"
    android:background="@drawable/background"
    android:measureAllChildren="false"
    android:minHeight="75dp"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".Itinerary" >

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

任何帮助将不胜感激，因为我刚刚碰壁。我搜索了其他问题，但没有一个有效/或者我不明白它们是如何工作的。

Answer 1

我完全不明白你为什么要在处理程序中这样做。这个:

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

放入 onCreate() 方法将返回 GoogleMap 对象。