Geocoder initialization fails

问题

I am getting a NullPointerException when trying to declare the Geocoder in my application. I have the following declaration :

public class MainActivity extends Activity {

private Geocoder geocoder = new Geocoder(this, Locale.getDefault());

    ...
 }

I get the following LogCat :

03-20 10:48:55.729: D/AndroidRuntime(604): Shutting down VM
03-20 10:48:55.729: W/dalvikvm(604): threadid=1: thread exiting with uncaught exception 

(group=0x40a71930)
03-20 10:48:56.209: E/AndroidRuntime(604): FATAL EXCEPTION: main
03-20 10:48:56.209: E/AndroidRuntime(604): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.coord/com.example.coord.MainActivity}: java.lang.NullPointerException
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.os.Looper.loop(Looper.java:137)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.app.ActivityThread.main(ActivityThread.java:5041)
03-20 10:48:56.209: E/AndroidRuntime(604):  at java.lang.reflect.Method.invokeNative(Native Method)
03-20 10:48:56.209: E/AndroidRuntime(604):  at java.lang.reflect.Method.invoke(Method.java:511)
03-20 10:48:56.209: E/AndroidRuntime(604):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-20 10:48:56.209: E/AndroidRuntime(604):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-20 10:48:56.209: E/AndroidRuntime(604):  at dalvik.system.NativeStart.main(Native Method)
03-20 10:48:56.209: E/AndroidRuntime(604): Caused by: java.lang.NullPointerException
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:109)
03-20 10:48:56.209: E/AndroidRuntime(604):  at com.example.coord.MainActivity.<init>(MainActivity.java:21)
03-20 10:48:56.209: E/AndroidRuntime(604):  at java.lang.Class.newInstanceImpl(Native Method)
03-20 10:48:56.209: E/AndroidRuntime(604):  at java.lang.Class.newInstance(Class.java:1319)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
03-20 10:48:56.209: E/AndroidRuntime(604):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)

Line 21 is my Geocoder declaration. What is wrong with my code?

回答1:

The context is only available when the activity is started so you cannot initialize the geocoder in the class body. Try to initialize it in the onCreate or onResume method instead...

public class MainActivity extends Activity {
  private Geocoder mGeocoder;

  @Override
  protected void onCreate(Bundle _icicle) {
    super.onCreate(_icicle);
    mGeocoder = new Geocoder(getApplicationContext(), Locale.getDefault());
  }
}

回答2:

Add this permissions in to manifest

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

and use getApplicationContext() insted of this

回答3:

It is recommended to use the GeoCode in Background or on separate thread as defined by Google Developers page.

new Thread(new Runnable() 
                    {
                        @Override
                        public void run() 
                        {
                            //Do things.
                            Geocoder geocoder = new Geocoder(getBaseContext());


                            try {
                                // Getting a maximum of 5 Address that matches the input text
                                addresses = geocoder.getFromLocationName(addressText,5);


                            } catch (IOException e) {
                                e.printStackTrace();
                            }

                        }

                    }).start();

来源：https://stackoverflow.com/questions/15521592/geocoder-initialization-fails