修改:
现在该应用正在运行。但它只是在第一次启动后(安装后)请求许可。如果我离开应用程序(按下后退按钮),然后再启动它,它不会要求许可。为什么会这样?
不按后退按钮会通过调用onDestroy()来破坏活动,是否应该再次调用onCreate()方法?
原始问题
我的应用程序允许用户在按下按钮时找到他们当前的位置。每当应用程序第一次启动时,它会询问用户权限,但在授予权限时崩溃会发生以下错误:
java.lang.RuntimeException: Failure delivering result
ResultInfo{who=@android:requestPermissions:, request=10, result=-1,
data=Intent { act=android.content.pm.action.REQUEST_PERMISSIONS (has
extras) }} to activity
{com.example.hpi5.location/com.example.hpi5.location.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
以下是我的活动代码:
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.Manifest;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.content.pm.PackageManager;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
Button button ;
LocationListener locationListener;
LocationManager locationManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (Build.VERSION.SDK_INT >=23 ){
if (checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
10);
return;
}
}
button = (Button) findViewById(R.id.button);
locationManager = (LocationManager)
getSystemService(LOCATION_SERVICE);
locationListener = new LocationListener()
{
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onLocationChanged(Location location) {
// TODO Auto-generated method stub
double latitude = location.getLatitude();
double longitude = location.getLongitude();
//double speed = location.getSpeed(); //spe2d in meter/minute
//speed = (speed*3600)/1000; // speed in km/minute
Toast.makeText(getApplicationContext(), "lat" + latitude + "lon" + longitude,Toast.LENGTH_SHORT).show();
}
};
}
void requestUpdate(){
button.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view) {
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
}
});
}
@Override
public void onRequestPermissionsResult(int requestCode,
@NonNull String permissions[], @ NonNull int[] grantResults) {
switch (requestCode) {
case -1:{
//hello
}
case 10: {
if (grantResults.length>0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
requestUpdate();
}
}
}
}
}
以下是logcat错误:
java.lang.RuntimeException: Failure delivering result
ResultInfo{who=@android:requestPermissions:, request=10, result=-1,
data=Intent { act=android.content.pm.action.REQUEST_PERMISSIONS (has
extras) }} to activity
{com.example.hpi5.location/com.example.hpi5.location.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
at android.app.ActivityThread.deliverResults(ActivityThread.java:3699)
at
android.app.ActivityThread.handleSendResult(ActivityThread.java:3742)
at android.app.ActivityThread.-wrap16(ActivityThread.java)
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1393)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual
method 'void
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
com.example.hpi5.location.MainActivity.requestUpdate(MainActivity.java:80)
com.example.hpi5.location.MainActivity.onRequestPermissionsResult(MainActivity.java:95)
android.app.Activity.dispatchRequestPermissionsResult(Activity.java:6553)
at android.app.Activity.dispatchActivityResult(Activity.java:6432)
at android.app.ActivityThread.deliverResults(ActivityThread.java:3695)
android.app.ActivityThread.handleSendResult(ActivityThread.java:3742)
at android.app.ActivityThread.-wrap16(ActivityThread.java)
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1393)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
答案 0 :(得分:4)
编辑Coarse Permission
,按钮初始化。 onCreate()
并将ponit添加为onRequestPermissionsResult()
。
由于NullPointException
的空对象引起的错误是Button
:
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.Manifest;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.content.pm.PackageManager;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
Button button ;
LocationListener locationListener;
LocationManager locationManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view) {
requestUpdate();
}
});
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M){
if (checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION)
!= PackageManager.PERMISSION_GRANTED &&
ActivityCompat.checkSelfPermission
(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION,},
10);
return;
}
}
locationManager = (LocationManager)
getSystemService(LOCATION_SERVICE);
locationListener = new LocationListener()
{
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onLocationChanged(Location location) {
// TODO Auto-generated method stub
double latitude = location.getLatitude();
double longitude = location.getLongitude();
//double speed = location.getSpeed(); //spe2d in meter/minute
//speed = (speed*3600)/1000; // speed in km/minute
Toast.makeText(getApplicationContext(), "lat" + latitude + "lon" + longitude,Toast.LENGTH_SHORT).show();
}
};
}
void requestUpdate(){
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
}
@Override
public void onRequestPermissionsResult(int requestCode,
@NonNull String permissions[], @ NonNull int[] grantResults) {
switch (requestCode) {
case -1:
//hello
break;
case 10:
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
requestUpdate();
}else{
//do something if permission not granted.
}
break;
}
}
}
答案 1 :(得分:2)
在初始化button
之前请求权限,我假设回调在有机会完全初始化Button对象之前完成。尝试将权限检查移至onCreate
的末尾,如果没有,请仔细检查按钮的ID是否正确。
答案 2 :(得分:0)
移动线
button = (Button) findViewById(R.id.button);
到
之后的位置setContentView(..);