我正在构建一个 Android 应用程序，它使用 LocationManager 从用户处获取纬度和经度，然后将这些变量输入 URL，该 URL 在 WebView 中打开。
出于某种原因，在某些 Android 设备和我的 Eclipse 模拟器上，当此 Activity 尝试打开时应用程序崩溃。我的崩溃报告中出现 NPE 错误。
我已将错误确定为以下两行代码:
double longitude = lastKnownLocation.getLongitude();
double latitude = lastKnownLocation.getLatitude();
当我将这两个变量设置为静态值(例如 1)时，应用程序可以正确运行。
下面是我的完整 page1.activity。有人可以帮忙吗？
package com.xxx.yyy;
import android.annotation.SuppressLint;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.webkit.GeolocationPermissions;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.webkit.GeolocationPermissions.Callback;
import com.xxx.yyy.R;
import com.actionbarsherlock.view.MenuItem;
import com.devspark.sidenavigation.ISideNavigationCallback;
import com.devspark.sidenavigation.SideNavigationView;
public class page1 extends MainActivity implements ISideNavigationCallback, GeolocationPermissions.Callback {
public static final String EXTRA_TITLE = "com.devspark.sidenavigation.sample.extra.MTGOBJECT";
public static final String EXTRA_RESOURCE_ID = "com.devspark.sidenavigation.sample.extra.RESOURCE_ID";
private ImageView icon;
private SideNavigationView sideNavigationView;
ProgressDialog mProgress;
@SuppressLint("SetJavaScriptEnabled")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_page1);
icon = (ImageView) findViewById(android.R.id.icon);
sideNavigationView = (SideNavigationView) findViewById(R.id.side_navigation_view);
sideNavigationView.setMenuItems(R.menu.side_navigation_menu);
sideNavigationView.setMenuClickCallback(this);
if (getIntent().hasExtra(EXTRA_TITLE)) {
String title = getIntent().getStringExtra(EXTRA_TITLE);
int resId = getIntent().getIntExtra(EXTRA_RESOURCE_ID, 0);
setTitle(title);
icon.setImageResource(resId);
}
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
//Get webview layout
WebView engine = (WebView) findViewById(R.id.webView1);
//loading
mProgress = ProgressDialog.show(this, "Loading", "Finding locations near you");
engine.setWebChromeClient(new WebChromeClient() {
@Override
public void onProgressChanged(WebView view, int progress)
{
}
});
engine.setWebViewClient(new FixedWebViewClient() {
@Override
public void onPageStarted(WebView view, String url, Bitmap favicon)
{
findViewById(R.id.progressBar1).setVisibility(view.VISIBLE);
}
@Override
public void onPageFinished(WebView view, String url){
findViewById(R.id.progressBar1).setVisibility(view.GONE);
if(mProgress.isShowing()) {
mProgress.dismiss(); }
//error handeling
}
@Override
public void onReceivedError(WebView webView, int errorCode, String description, String failingUrl) {
try {
webView.stopLoading();
} catch (Exception e) {
}
try {
webView.clearView();
} catch (Exception e) {
}
if (webView.canGoBack()) {
webView.goBack();
}
webView.loadUrl("file:///android_asset/error.html"); //background to message dialog, or page you want to load if requested page is offline
AlertDialog alertDialog = new AlertDialog.Builder(page1.this).create(); //remove these 4 rules if you load an assets page instead.
alertDialog.setTitle("Error");
alertDialog.setMessage("No internet connection was found!");
alertDialog.setButton("Retry", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
finish();
startActivity(getIntent());
}
});
alertDialog.show();
super.onReceivedError(webView, errorCode, description, failingUrl);
}
});
LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
LocationListener locationListener = new LocationListener() {
public void onLocationChanged(Location location) {
// Called when a new location is found by the network location provider.
double longitude = location.getLongitude();
double latitude = location.getLatitude();
}
public void onStatusChanged(String provider, int status, Bundle extras) {}
public void onProviderEnabled(String provider) {}
public void onProviderDisabled(String provider) {}
};
// Register the listener with the Location Manager to receive location updates
lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
String locationProvider = LocationManager.NETWORK_PROVIDER;
// Or use LocationManager.GPS_PROVIDER
Location lastKnownLocation = lm.getLastKnownLocation(locationProvider);
double longitude = lastKnownLocation.getLongitude();
double latitude = lastKnownLocation.getLatitude();
engine.loadUrl("http://www.turn2clients.com/app/home/iPhone/dev/?s=&geo-radius=3&geo=on&geo-lat="+latitude+"&geo-lng="+longitude+"&categories=0&locations=0&dir-search=yes");
//if you would like to load local assets file, replace with file:///android_asset/error.html
}
public void invoke(String origin, boolean allow, boolean remember) {
}
final class GeoClient extends WebChromeClient {
@Override
public void onGeolocationPermissionsShowPrompt(String origin,
Callback callback) {
}
}
private class FixedWebViewClient extends WebViewClient {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
view.loadUrl(url);
//start a new application/activity (in this case youtube) if url starts with
if (url.startsWith("mlb")){
return true;
}
else
{
view.loadUrl(url);
return true;
}
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
sideNavigationView.toggleMenu();
break;
default:
return super.onOptionsItemSelected(item);
}
return true;
}
@Override
public void onSideNavigationItemClick(int itemId) {
switch (itemId) {
case R.id.side_navigation_menu_item1:
Intent page1 = new Intent(this, page1.class);
startActivity(page1);
break;
case R.id.side_navigation_menu_item2:
Intent page2 = new Intent(this, page2.class);
startActivity(page2);
break;
case R.id.side_navigation_menu_item3:
Intent page3 = new Intent(this, page3.class);
startActivity(page3);
break;
default:
return;
}
finish();
}
@Override
public void onBackPressed() {
//This part will close you app if a certain url is visited, ofcourse you can replace this with any other action.
WebView engine = (WebView) findViewById(R.id.webView1);
String url = engine.getUrl();
if (url.equals("http://closeifthisurlisvisited.com/") ||
url.equals("http://alsocloseifthisurlisvisited.com")) {
// exit
super.onBackPressed();
} else {
// Go back when back button is pressed
engine.goBack();
}
//thats it
// hide menu if it shown with backbutton
if (sideNavigationView.isShown()) {
sideNavigationView.hideMenu();
} else {
//super.onBackPressed();
}
}
/**
* Start activity from SideNavigation.
*
* @param title
* title of Activity
* @param resId
* resource if of background image
*/
private void invokeActivity(String title, int resId) {
Intent intent = new Intent(this, MainActivity.class);
intent.putExtra(EXTRA_TITLE, title);
intent.putExtra(EXTRA_RESOURCE_ID, resId);
// all of the other activities on top of it will be closed and this
// Intent will be delivered to the (now on top) old activity as a
// new Intent.
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
// no animation of transition
overridePendingTransition(0, 0);
}
}
最佳答案
最好的方法是使用 CWAC 的位置服务 Location Poller 服务已经为我们提供了使用它，只需给出唤醒它的时间间隔
按照这样的方式进行操作，您将需要 jar 文件，您可以从[此处] https://www.dropbox.com/sh/pgxk2v9l5vl0h2j/3svyZnuwOK/CWAC-LocationPoller.jar 获取该文件。
从您的 Activity 中启动 LocationPoller 并将闹钟设置为您想要的重复时间
AlarmManager alarmMgr = (AlarmManager) getSystemService(ALARM_SERVICE);
Intent i = new Intent(this, LocationPoller.class);
Bundle bundle = new Bundle();
LocationPollerParameter parameter = new LocationPollerParameter(bundle);
parameter.setIntentToBroadcastOnCompletion(new Intent(this,
LocationReceiver.class));
// try GPS and fall back to NETWORK_PROVIDER
parameter.setProviders(new String[] { LocationManager.GPS_PROVIDER });
parameter.setTimeout(120000);
i.putExtras(bundle);
PendingIntent pi = PendingIntent.getBroadcast(this, 0, i, 0);
alarmMgr.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP,
SystemClock.elapsedRealtime(), 300000, pi);
创建一个接收器类位置接收器，从中获取经纬度
public class LocationReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
try {
Bundle b=intent.getExtras();
LocationPollerResult locationResult = new LocationPollerResult(b);
Location loc=locationResult.getLocation();
String msg;
if (loc==null) {
loc=locationResult.getLastKnownLocation();
if (loc==null) {
msg=locationResult.getError();
}
else {
msg="TIMEOUT, lastKnown="+loc.toString();
}
}
else {
msg=loc.toString();
Log.i("Location Latitude", String.valueOf(loc.getLatitude()));
Log.i("Location Longitude", String.valueOf(loc.getLongitude()));
Log.i("Location Accuracy", String.valueOf(loc.getAccuracy()));
}
Log.i(getClass().getSimpleName(), "received location: " + msg);
}
catch (Exception e) {
Log.e(getClass().getName(), e.getMessage());
}
}
并将其添加到您的 list 中
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<receiver android:name="com.commonsware.cwac.locpoll.LocationPoller" />
<service android:name="com.commonsware.cwac.locpoll.LocationPollerService" />
以及接收者声明，您将在其中获取所有内容
<receiver android:name="com.RareMediaCompany.Helios.LocationReceiver" />
关于java NullPointerException 与 LocationManager，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21635386/