权限 java.lang.NullPointerException： 尝试调用虚拟方法 'android.content.Context android.content.Context.getApp

Question

我正在运行关于设置权限的错误。我在清单中声明了位置和互联网权限，并调用checkPermission()和onRequestPermissionsResult来显示权限对话框。然而，我无法启动我的应用程序，并收到相同的错误。

我试过了

private val hasFineLocationPermission = ActivityCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION)

我改变了context如applicationContext, this@MainActivity, MainActivity@This，但我仍然收到相同的错误。

MainActivity

class MainActivity : AppCompatActivity() {
private lateinit var binding : ActivityMainBinding
private var REQUIRED_PERMISSIONS = arrayOf<String>(
Manifest.permission.ACCESS_FINE_LOCATION,
Manifest.permission.ACCESS_BACKGROUND_LOCATION)
private val context : Context = applicationContext
private val hasFineLocationPermission = ActivityCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION)
private val hasBackgroundLocationPermission = ActivityCompat.checkSelfPermission(context, Manifest.permission.ACCESS_BACKGROUND_LOCATION)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
checkPermission()
}
fun checkPermission() {
if (hasFineLocationPermission == PackageManager.PERMISSION_GRANTED
) {
// Fine Location permission is granted
// Check if current android version >= 11, if >= 11 check for Background Location permission
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
if (hasBackgroundLocationPermission == PackageManager.PERMISSION_GRANTED
) {
// Background Location Permission is granted so do your work here
} else {
// Ask for Background Location Permission
askPermissionForBackgroundUsage()
}
}
} else {
// Fine Location Permission is not granted so ask for permission
askForLocationPermission();
}
}
private fun askForLocationPermission() {
if (ActivityCompat.shouldShowRequestPermissionRationale(this@MainActivity,
Manifest.permission.ACCESS_FINE_LOCATION)
) {
AlertDialog.Builder(this)
.setTitle("Permission Needed!")
.setMessage("Location Permission Needed!")
.setPositiveButton("OK", DialogInterface.OnClickListener { dialogInterface, int ->
ActivityCompat.requestPermissions(this@MainActivity, arrayOf(
Manifest.permission.ACCESS_FINE_LOCATION), hasFineLocationPermission)
})
.setNegativeButton("CANCEL", DialogInterface.OnClickListener { dialogInterface, int ->
// Permission is denied by the user
throw RuntimeException("denied")
})
.create().show()
} else {
ActivityCompat.requestPermissions(this,
arrayOf(Manifest.permission.ACCESS_FINE_LOCATION), hasFineLocationPermission)
}
}
private fun askPermissionForBackgroundUsage() {
if (ActivityCompat.shouldShowRequestPermissionRationale(this@MainActivity,
Manifest.permission.ACCESS_BACKGROUND_LOCATION)
) {
AlertDialog.Builder(this)
.setTitle("Permission Needed!")
.setMessage("Background Location Permission Needed!, tap "Allow all time in the next screen"")
.setPositiveButton("OK", DialogInterface.OnClickListener { dialogInterface, int ->
ActivityCompat.requestPermissions(this@MainActivity,
arrayOf(Manifest.permission.ACCESS_BACKGROUND_LOCATION), hasBackgroundLocationPermission)
})
.setNegativeButton("CANCEL", DialogInterface.OnClickListener { dialogInterface, int ->
// Permission is denied by the user
throw RuntimeException("denied")
})
.create().show()
} else {
ActivityCompat.requestPermissions(this,
arrayOf(Manifest.permission.ACCESS_BACKGROUND_LOCATION), hasBackgroundLocationPermission)
}
}
override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults)
//        if (requestCode == PERMISSIONS_REQUEST_CODE && grantResults.size == 
REQUIRED_PERMISSIONS.size) {
if (requestCode ==  hasFineLocationPermission) {
if (grantResults[0] == PackageManager.PERMISSION_GRANTED){
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R){
if (hasBackgroundLocationPermission == PackageManager.PERMISSION_GRANTED) {
//                        var check_result = true
//                        for (result in grantResults) {
//                            if (result != PackageManager.PERMISSION_GRANTED) {
//                                check_result = false;
//                                break;
//                            }
//                        }
} else {
askPermissionForBackgroundUsage()
}
}
} else {
if (ActivityCompat.shouldShowRequestPermissionRationale(this,
REQUIRED_PERMISSIONS[0])
) {
Toast.makeText(this,
"denied",
Toast.LENGTH_SHORT).show()
finish()
} else {
Toast.makeText(this, "denied", Toast.LENGTH_SHORT)
.show()
}
}
} else if (requestCode == hasBackgroundLocationPermission) {
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// User granted for Background Location Permission.
} else {
ActivityCompat.shouldShowRequestPermissionRationale(this,
REQUIRED_PERMISSIONS[1])
}
}
}
}

Answer 1

活动不会初始化，直到onCreate被调用。这意味着在此之前你不能使用像getApplicationContext这样的函数。基本上，Activities不应该有init块。如果onCreate依赖于上下文，它们应该运行onCreate中的所有内容。