ContextCompat.checkSelfPermission 관련 NullPointerException

Question

안드로이드 초보입니다. 카메라 버튼을 누르고 권한을 받지않은 경우 권한요청하고 권한 받은 경우 카메라 앱을 실행하는 코드를 작성중인데  로그캣에 따르면 checkPermission에서 NullPointerException가 발생하고있습니다 ㅠ어떻게 해줘야할지요..

 

[코드]

package com.ooh.review

import android.Manifest
import android.content.Intent
import android.content.pm.PackageManager
import android.os.Bundle
import android.provider.MediaStore
import android.util.Log
import android.widget.ImageView
import androidx.appcompat.app.AppCompatActivity
import androidx.core.content.ContextCompat
import com.ooh.review.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {
    val binding by lazy { ActivityMainBinding.inflate(layoutInflater) }
    val REQ_CAMERA = 101
    val REQ_STORAGE = 102
    val cameraPermission = ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(binding.root)

        setView()
    }
    fun setView(){
        binding.buttonCamera.setOnClickListener{
//            if (cameraPermission == PackageManager.PERMISSION_DENIED){
//                Log.d("my tag","권한이 필요하다고")
//            } else {
//
//            }

        }
        binding.buttonGallery.setOnClickListener{
            openGallery()
        }
    }
    fun openGallery(){
        val intent = Intent(Intent.ACTION_PICK)
        intent.type = MediaStore.Images.Media.CONTENT_TYPE
        startActivityForResult(intent, REQ_STORAGE)
    }
}

[에러]

2021-10-16 15:08:10.049 10454-10454/com.ooh.review E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.ooh.review, PID: 10454
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.ooh.review/com.ooh.review.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Context.checkPermission(java.lang.String, int, int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3194)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Context.checkPermission(java.lang.String, int, int)' on a null object reference
        at android.content.ContextWrapper.checkPermission(ContextWrapper.java:762)
        at androidx.core.content.ContextCompat.checkSelfPermission(ContextCompat.java:555)
        at com.ooh.review.MainActivity.<init>(MainActivity.kt:18)
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1243)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3182)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

Answer 1

퍼미션 체크하는 위치가 이상해 보입니다. 작성하신 코드는 액티비티가 초기화되기 이전에 퍼미션을 체크하고 있기 때문에 context가 null이 될 수 있습니다. 퍼미션 체크하는 

fun setView(){
        binding.buttonCamera.setOnClickListener{
              if (!hasCameraPermission()) {
                    //request permission
                    return
              }

//            if (cameraPermission == PackageManager.PERMISSION_DENIED){
//                Log.d("my tag","권한이 필요하다고")
//            } else {
//
//            }

        }

        binding.buttonGallery.setOnClickListener{
            if (!hasCameraPermission()) {
                    //request permission
                    return
              } 

            openGallery()
        }
    }
    fun openGallery(){
        val intent = Intent(Intent.ACTION_PICK)
        intent.type = MediaStore.Images.Media.CONTENT_TYPE
        startActivityForResult(intent, REQ_STORAGE)
    }
}

private fun hasCameraPermission(): Boolean {
   return ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) == Packagemanager.PERMISSION_GRANTED
}

위처럼, 코드를 퍼미션을 사용하기 직전에 호출해 보세요. 그래야 Context가 초기화 된 상태라 null이 되지 않을 것 같습니다.

 

 

Comments

안녕하세요 답변 너무 감사드립니다.
cameraPermission 초기화 위치를 onCreate 전에 했었는데 위치를 해당 함수 속으로 바꿨더니 해결되었습니다. 무슨차이가 있는지 모르겠지만 ㅠㅠ 아무튼 감사합니다.

---

Activity를 보시면 님이 직접 생성할 수가 없습니다. startActvity등을 통해 안드로이드 시스템이 생성하도록 만들어 주어야 합니다. Activity클래스의 onCreate메소드의 소스를 따라가보면

 @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        // Restore the Saved State first so that it is available to
        // OnContextAvailableListener instances
        mSavedStateRegistryController.performRestore(savedInstanceState);
        mContextAwareHelper.dispatchOnContextAvailable(this);
        super.onCreate(savedInstanceState);
        ReportFragment.injectIfNeededIn(this);
        if (mContentLayoutId != 0) {
            setContentView(mContentLayoutId);
        }
    }

public void dispatchOnContextAvailable(@NonNull Context context) {
        mContext = context;  // <--- 여기서 초기화가 됨.
        for (OnContextAvailableListener listener : mListeners) {
            listener.onContextAvailable(context);
        }
}
 

위처럼 onCreate 안에서 mContext가 초기화 되고 있습니다. 따라서 Activity안에서 context에 접근하려면 onCreate에서 super.onCreate가 호출된 뒤에 해야됩니다.