我正在为学校创建一个带有mapfragment和按钮的项目，但当我尝试访问我的地图时，它完全崩溃了 这是我的代码：
package com.helloandroid.mapview;
import android.app.FragmentManager;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import com.google.android.gms.maps.*;
import com.google.android.gms.maps.model.*;
public class MainActivity extends ActionBarActivity {
GoogleMap myMap;
Button btnShow;
@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();
}
btnShow = (Button) findViewById(R.id.btnShow);
这是它崩溃的地方：
SupportMapFragment mapFrag = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
myMap = mapFrag.getMap();
}
/**
* A placeholder fragment containing a simple view.
*/
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);
return rootView;
}
}
}
这是我的logcat结果：
01-09 20:19:57.475 28744-28744/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.helloandroid.mapview/com.helloandroid.mapview.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2306)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358)
at android.app.ActivityThread.access$600(ActivityThread.java:156)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1340)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:153)
at android.app.ActivityThread.main(ActivityThread.java:5297)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.helloandroid.mapview.MainActivity.onCreate(MainActivity.java:34)
at android.app.Activity.performCreate(Activity.java:5122)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358)
at android.app.ActivityThread.access$600(ActivityThread.java:156)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1340)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:153)
at android.app.ActivityThread.main(ActivityThread.java:5297)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
这是mapfragment
<fragment
android:id="@+id/map"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:name="com.google.android.gms.maps.MapFragment"
android:layout_below="@+id/btnShow" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Show"
android:id="@+id/btnShow"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
有谁知道如何解决这个问题？
提前致谢
答案 0 :(得分：3)
首先，您需要检查设备是否具有正确的Google Play服务，如果设备没有正确设置，您将无法使用地图。
if (GooglePlayServicesUtil.isGooglePlayServicesAvailable(this) != ConnectionResult.SUCCESS) {
// Handle the case here
}
其次，您无法保证地图准备就绪，因此您需要尝试多次设置地图，例如从OnCreate(..)和onResume(..)调用此方法。
private void setUpMapIfNeeded() {
// Do a null check to confirm that we have not already instantiated the map.
if (mMap == null) {
// Try to obtain the map from the SupportMapFragment.
mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
// Check if we were successful in obtaining the map.
if (mMap != null) {
// here you can setup the map the way you want
}
}
}
访问SupportMapFragment时，您获得了NullPointerException？请检查以下内容：
如果您仍然遇到问题，则应该为地图片段添加xml。
您的XML设置应具有此
class="com.google.android.gms.maps.SupportMapFragment"，即从片段中删除android:name属性并添加该类。
答案 1 :(得分：1)
在您的xml文件中写道：
android:name="com.google.android.gms.maps.MapFragment"
在您的java代码中，您可以通过
访问它SupportMapFragment mapFrag = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
因此，您只需要从
进行更改android:name="com.google.android.gms.maps.MapFragment"
到
android:name="com.google.android.gms.maps.SupportMapFragment"
在你的xml文件中。
答案 2 :(得分：0)
简单替换
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android
android:id="@+id/map"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
class="com.google.android.gms.maps.SupportMapFragment" />
用这个
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/map"
android:name="com.google.android.gms.maps.MapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent" />
并像这样访问Mapview
GoogleMap googleMap;
..
..
googleMap = ((MapFragment) getActivity().getFragmentManager()
.findFragmentById(R.id.map)).getMap();
googleMap.getUiSettings().setZoomControlsEnabled(true);
希望它会对某人有所帮助。