i'm new android , when googled issue couldn't find proper solution problem.
i'm trying develop location based android app can find user location automatically. code compiles without error in android studio manager, when click on show location button, application exists , display error unfortunately, testgps has stopped
androidmanifest.xml
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.lsdias.testgps" > <application android:allowbackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:theme="@style/apptheme" > <activity android:name=".gpstracker" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.main" /> <category android:name="android.intent.category.launcher" /> </intent-filter> </activity> </application> <uses-permission android:name="android.permission.access_fine_location" /> <uses-permission android:name="android.permission.internet" /> </manifest> gpstracker.java
package com.example.lsdias.testgps; import android.app.alertdialog; import android.content.context; import android.content.dialoginterface; import android.content.intent; import android.location.location; import android.location.locationlistener; import android.location.locationmanager; import android.provider.settings; import android.support.v7.app.actionbaractivity; import android.os.bundle; import android.view.menu; import android.view.menuitem; import android.util.log; import android.view.view; import android.widget.button; import android.widget.toast; public class gpstracker extends actionbaractivity implements locationlistener { button btnshowlocation; private final context mcontext; // flag gps status boolean isgpsenabled = false; // flag network status boolean isnetworkenabled = false; boolean cangetlocation = false; location location; // location double latitude; // latitude double longitude; // longitude // minimum distance change updates in meters private static final long min_distance_change_for_updates = 10; // 10 meters // minimum time between updates in milliseconds private static final long min_time_bw_updates = 1000 * 60 * 1; // 1 minute // declaring location manager protected locationmanager locationmanager; public gpstracker() { mcontext = null; } public gpstracker(context mcontext) { this.mcontext = mcontext; getlocation(); } public location getlocation() { try { locationmanager = (locationmanager) mcontext .getsystemservice(location_service); // getting gps status isgpsenabled = locationmanager .isproviderenabled(locationmanager.gps_provider); // getting network status isnetworkenabled = locationmanager .isproviderenabled(locationmanager.network_provider); if (!isgpsenabled && !isnetworkenabled) { // no network provider enabled } else { this.cangetlocation = true; // first location network provider if (isnetworkenabled) { locationmanager.requestlocationupdates( locationmanager.network_provider, min_time_bw_updates, min_distance_change_for_updates, this); log.d("network", "network"); if (locationmanager != null) { location = locationmanager .getlastknownlocation(locationmanager.network_provider); if (location != null) { latitude = location.getlatitude(); longitude = location.getlongitude(); } } } // if gps enabled lat/long using gps services if (isgpsenabled) { if (location == null) { locationmanager.requestlocationupdates( locationmanager.gps_provider, min_time_bw_updates, min_distance_change_for_updates, this); log.d("gps enabled", "gps enabled"); if (locationmanager != null) { location = locationmanager .getlastknownlocation(locationmanager.gps_provider); if (location != null) { latitude = location.getlatitude(); longitude = location.getlongitude(); } } } } } } catch (exception e) { e.printstacktrace(); } return location; } @override protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_gpstracker); btnshowlocation = (button) findviewbyid(r.id.button_location); // show location button click event btnshowlocation.setonclicklistener(new view.onclicklistener() { @override public void onclick(view v) { if(cangetlocation()) { double latitude = getlatitude(); double longitude = getlongitude(); // \n new line toast.maketext(getapplicationcontext(), "your location - \nlat: " + latitude + "\nlong: " + longitude, toast.length_long).show(); } else { // can't location // gps or network not enabled // ask user enable gps/network in settings showsettingsalert(); } } }); } @override public boolean oncreateoptionsmenu(menu menu) { // inflate menu; adds items action bar if present. getmenuinflater().inflate(r.menu.menu_gpstracker, menu); return true; } @override public boolean onoptionsitemselected(menuitem item) { // handle action bar item clicks here. action bar // automatically handle clicks on home/up button, long // specify parent activity in androidmanifest.xml. int id = item.getitemid(); //noinspection simplifiableifstatement if (id == r.id.action_settings) { return true; } return super.onoptionsitemselected(item); } @override public void onlocationchanged(location location) { } @override public void onstatuschanged(string provider, int status, bundle extras) { } @override public void onproviderenabled(string provider) { } @override public void onproviderdisabled(string provider) { } /** * function latitude * */ public double getlatitude(){ if(location != null){ latitude = location.getlatitude(); } // return latitude return latitude; } /** * function longitude * */ public double getlongitude(){ if(location != null){ longitude = location.getlongitude(); } // return longitude return longitude; } /** * function check if best network provider * @return boolean * */ public boolean cangetlocation() { return this.cangetlocation; } /** * function show settings alert dialog * */ public void showsettingsalert(){ alertdialog.builder alertdialog = new alertdialog.builder(mcontext); // setting dialog title alertdialog.settitle("gps settings"); // setting dialog message alertdialog.setmessage("gps not enabled. want go settings menu?"); // setting icon dialog //alertdialog.seticon(r.drawable.delete); // on pressing settings button alertdialog.setpositivebutton("settings", new dialoginterface.onclicklistener() { public void onclick(dialoginterface dialog,int which) { intent intent = new intent(settings.action_location_source_settings); mcontext.startactivity(intent); } }); // on pressing cancel button alertdialog.setnegativebutton("cancel", new dialoginterface.onclicklistener() { public void onclick(dialoginterface dialog, int which) { dialog.cancel(); } }); // showing alert message alertdialog.show(); } /** * stop using gps listener * calling function stop using gps in app * */ public void stopusinggps(){ if(locationmanager != null){ locationmanager.removeupdates(gpstracker.this); } } } logcat
09-02 12:47:51.902 1935-1935/com.example.lsdias.testgps i/art﹕ not late-enabling -xcheck:jni (already on) 09-02 12:47:52.384 1935-1958/com.example.lsdias.testgps d/openglrenderer﹕ render dirty regions requested: true 09-02 12:47:52.385 1935-1935/com.example.lsdias.testgps d/﹕ hostconnection::get() new host connection established 0xa6c40550, tid 1935 09-02 12:47:52.418 1935-1935/com.example.lsdias.testgps d/atlas﹕ validating map... 09-02 12:47:52.582 1935-1949/com.example.lsdias.testgps i/art﹕ background sticky concurrent mark sweep gc freed 4140(288kb) allocspace objects, 0(0b) los objects, 28% free, 810kb/1135kb, paused 61.733ms total 123.372ms 09-02 12:47:52.607 1935-1958/com.example.lsdias.testgps d/﹕ hostconnection::get() new host connection established 0xa6c406b0, tid 1958 09-02 12:47:52.675 1935-1958/com.example.lsdias.testgps i/openglrenderer﹕ initialized egl, version 1.4 09-02 12:47:52.697 1935-1958/com.example.lsdias.testgps d/openglrenderer﹕ enabling debug mode 0 09-02 12:47:52.764 1935-1958/com.example.lsdias.testgps w/egl_emulation﹕ eglsurfaceattrib not implemented 09-02 12:47:52.764 1935-1958/com.example.lsdias.testgps w/openglrenderer﹕ failed set egl_swap_behavior on surface 0xa6c1ae20, error=egl_success 09-02 12:47:53.478 1935-1958/com.example.lsdias.testgps w/egl_emulation﹕ eglsurfaceattrib not implemented 09-02 12:47:53.478 1935-1958/com.example.lsdias.testgps w/openglrenderer﹕ failed set egl_swap_behavior on surface 0xa6c1ae20, error=egl_success 09-02 12:47:58.675 1935-1935/com.example.lsdias.testgps d/androidruntime﹕ shutting down vm --------- beginning of crash 09-02 12:47:58.675 1935-1935/com.example.lsdias.testgps e/androidruntime﹕ fatal exception: main process: com.example.lsdias.testgps, pid: 1935 java.lang.nullpointerexception: attempt invoke virtual method 'android.content.res.resources$theme android.content.context.gettheme()' on null object reference @ android.app.alertdialog.resolvedialogtheme(alertdialog.java:154) @ android.app.alertdialog$builder.<init>(alertdialog.java:379) @ com.example.lsdias.testgps.gpstracker.showsettingsalert(gpstracker.java:240) @ com.example.lsdias.testgps.gpstracker$1.onclick(gpstracker.java:155) @ android.view.view.performclick(view.java:4756) @ android.view.view$performclick.run(view.java:19749) @ android.os.handler.handlecallback(handler.java:739) @ android.os.handler.dispatchmessage(handler.java:95) @ android.os.looper.loop(looper.java:135) @ android.app.activitythread.main(activitythread.java:5221) @ java.lang.reflect.method.invoke(native method) @ java.lang.reflect.method.invoke(method.java:372) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:694) what's issue here?
the problem mcontext in gpstracker null, , creating alertdialog null context.
should not override activity's constructors. move getlocation(); oncreate() method
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