Androidフラッシュライトアプリが他のすべての起動時にクラッシュする

Question

私はアプリ開発を初めて使い、楽しみのために簡単な懐中電灯アプリを作りたかったのです。しかし、何らかの理由で私の懐中電灯アプリが1回おきにクラッシュする。私はonDestroy()メソッドが必要かもしれないと思ったが、それが問題なのかどうかはわからない。私はいつもNullPointerExceptionを得て、問題はonCreate()の方法のようです。助けてくれてありがとう！

package com.monstartech.superuser.flashlight; 

import android.annotation.SuppressLint; 
import android.support.v7.app.ActionBar; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.os.Handler; 
import android.view.MotionEvent; 
import android.view.View; 

import android.app.Activity; 
import android.app.AlertDialog; 
import android.content.DialogInterface; 
import android.content.pm.PackageManager; 
import android.hardware.Camera; 
import android.hardware.Camera.Parameters; 
import android.widget.ImageButton; 


/** 
* An example full-screen activity that shows and hides the system UI (i.e. 
* status bar and navigation/system bar) with user interaction. 
*/ 
public class FullscreenActivity extends AppCompatActivity { 


    //Camera variables: 
    private Camera camera; 
    ImageButton flashlightSwitchImg; 
    private boolean isFlashLightOn; 
    Parameters params; 


    /** 
    * Whether or not the system UI should be auto-hidden after 
    * {@link #AUTO_HIDE_DELAY_MILLIS} milliseconds. 
    */ 
    private static final boolean AUTO_HIDE = true; 

    /** 
    * If {@link #AUTO_HIDE} is set, the number of milliseconds to wait after 
    * user interaction before hiding the system UI. 
    */ 
    private static final int AUTO_HIDE_DELAY_MILLIS = 3000; 

    /** 
    * Some older devices needs a small delay between UI widget updates 
    * and a change of the status and navigation bar. 
    */ 
    private static final int UI_ANIMATION_DELAY = 300; 
    private final Handler mHideHandler = new Handler(); 
    private View mContentView; 


    private final Runnable mHidePart2Runnable = new Runnable() { 
     @SuppressLint("InlinedApi") 
     @Override 
     public void run() { 
      // Delayed removal of status and navigation bar 

      // Note that some of these constants are new as of API 16 (Jelly Bean) 
      // and API 19 (KitKat). It is safe to use them, as they are inlined 
      // at compile-time and do nothing on earlier devices. 
      mContentView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LOW_PROFILE 
        | View.SYSTEM_UI_FLAG_FULLSCREEN 
        | View.SYSTEM_UI_FLAG_LAYOUT_STABLE 
        | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY 
        | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION 
        | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION); 
     } 
    }; 

    private View mControlsView; 
    private final Runnable mShowPart2Runnable = new Runnable() { 
     @Override 
     public void run() { 
      // Delayed display of UI elements 
      ActionBar actionBar = getSupportActionBar(); 
      if (actionBar != null) { 
       actionBar.show(); 
      } 
      mControlsView.setVisibility(View.VISIBLE); 
     } 
    }; 
    private boolean mVisible; 
    private final Runnable mHideRunnable = new Runnable() { 
     @Override 
     public void run() { 
      hide(); 
     } 
    }; 
    /** 
    * Touch listener to use for in-layout UI controls to delay hiding the 
    * system UI. This is to prevent the jarring behavior of controls going away 
    * while interacting with activity UI. 
    */ 
    private final View.OnTouchListener mDelayHideTouchListener = new View.OnTouchListener() { 
     @Override 
     public boolean onTouch(View view, MotionEvent motionEvent) { 
      if (AUTO_HIDE) { 
       delayedHide(AUTO_HIDE_DELAY_MILLIS); 
      } 
      return false; 
     } 
    }; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_fullscreen); 

     mVisible = true; 
     mControlsView = findViewById(R.id.fullscreen_content_controls); 
     mContentView = findViewById(R.id.fullscreen_content); 

     // Set up the user interaction to manually show or hide the system UI. 
     mContentView.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       toggle(); 
      } 
     }); 


     // Upon interacting with UI controls, delay any scheduled hide() 
     // operations to prevent the jarring behavior of controls going away 
     // while interacting with the UI. 
     //TODO: uncoment? findViewById(R.id.dummy_button).setOnTouchListener(mDelayHideTouchListener); 

     //Camera Stuff's old spot 
     //Camera Stuff: 
     flashlightSwitchImg = (ImageButton) findViewById(R.id.flashlightSwitch); 
     boolean isCameraFlash = getApplicationContext().getPackageManager(). 
       hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH); 

     if(!isCameraFlash) { 
      showNoCameraAlert(); 
     } else { 
      camera = Camera.open(); 
      params = camera.getParameters(); 
     } 

     flashlightSwitchImg.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       if(isFlashLightOn) { 
        setFlashLightOff(); 
       } else { 
        setFlashLightOn(); 
       } 
      } 


     }); 
    } 

    private void showNoCameraAlert() { 
     new AlertDialog.Builder(this).setTitle("Error: No Camera Flash Found!!"). 
       setMessage("Camera flashlight not available in this Android device!"). 
       setPositiveButton(android.R.string.yes,new DialogInterface.OnClickListener() { 
        public void onClick(DialogInterface dialog, int which) { 
         finish(); 
        } 
       }) 
       .setIcon(android.R.drawable.ic_dialog_alert) 
       .show(); 
     return; 
    } 

    //setFlashLightOn 
    private void setFlashLightOn() { 
     params = camera.getParameters(); 
     params.setFlashMode(Parameters.FLASH_MODE_TORCH); 
     camera.setParameters(params); 
     camera.startPreview(); 
     isFlashLightOn = true; 
     flashlightSwitchImg.setImageResource(R.drawable.light_on); 
    } 

    //setFlashLightOff 
    private void setFlashLightOff() { 
     params.setFlashMode(Parameters.FLASH_MODE_OFF); 
     camera.setParameters(params); 
     camera.stopPreview(); 
     isFlashLightOn = false; 
     flashlightSwitchImg.setImageResource(R.drawable.light_off); 
    } 

    @Override 
    protected void onStop() { 
     super.onStop(); 
     if(camera != null) { 
      camera.release(); 
      camera = null; 
     } 
    } 
    //end Camera stuff 




    @Override 
    protected void onPostCreate(Bundle savedInstanceState) { 
     super.onPostCreate(savedInstanceState); 

     // Trigger the initial hide() shortly after the activity has been 
     // created, to briefly hint to the user that UI controls 
     // are available. 
     delayedHide(100); 
    } 

    private void toggle() { 
     if (mVisible) { 
      hide(); 
     } else { 
      show(); 
     } 
    } 

    private void hide() { 
     // Hide UI first 
     ActionBar actionBar = getSupportActionBar(); 
     if (actionBar != null) { 
      actionBar.hide(); 
     } 
     mControlsView.setVisibility(View.GONE); 
     mVisible = false; 

     // Schedule a runnable to remove the status and navigation bar after a delay 
     mHideHandler.removeCallbacks(mShowPart2Runnable); 
     mHideHandler.postDelayed(mHidePart2Runnable, UI_ANIMATION_DELAY); 
    } 

    @SuppressLint("InlinedApi") 
    private void show() { 
     // Show the system bar 
     mContentView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN 
       | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION); 
     mVisible = true; 

     // Schedule a runnable to display UI elements after a delay 
     mHideHandler.removeCallbacks(mHidePart2Runnable); 
     mHideHandler.postDelayed(mShowPart2Runnable, UI_ANIMATION_DELAY); 
    } 

    /** 
    * Schedules a call to hide() in [delay] milliseconds, canceling any 
    * previously scheduled calls. 
    */ 
    private void delayedHide(int delayMillis) { 
     mHideHandler.removeCallbacks(mHideRunnable); 
     mHideHandler.postDelayed(mHideRunnable, delayMillis); 
    } 

    @Override 
    protected void onDestroy(){ 
     super.onDestroy(); 
     //Your code 
    } 
} 

Logcat

05-11 15:11:39.793 18729-18729/com.monstartech.superuser.flashlight D/Activity: #1 setTransGradationModeColor false 
05-11 15:11:40.583 18729-18729/com.monstartech.superuser.flashlight D/ViewRootImpl: ViewPostImeInputStage ACTION_DOWN 
05-11 15:11:40.653 18729-18729/com.monstartech.superuser.flashlight D/AndroidRuntime: Shutting down VM 
05-11 15:11:40.653 18729-18729/com.monstartech.superuser.flashlight W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x41d01da0) 
05-11 15:11:40.653 18729-18729/com.monstartech.superuser.flashlight E/AndroidRuntime: FATAL EXCEPTION: main 
                         Process: com.monstartech.superuser.flashlight, PID: 18729 
                         java.lang.NullPointerException 
    at com.monstartech.superuser.flashlight.FullscreenActivity.setFlashLightOn(FullscreenActivity.java:173) 
    at com.monstartech.superuser.flashlight.FullscreenActivity.access$700(FullscreenActivity.java:24) 
    at com.monstartech.superuser.flashlight.FullscreenActivity$6.onClick(FullscreenActivity.java:150) 
    at android.view.View.performClick(View.java:4754) 
    at android.view.View$PerformClick.run(View.java:19591) 
    at android.os.Handler.handleCallback(Handler.java:733) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:146) 
    at android.app.ActivityThread.main(ActivityThread.java:5731) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107) 
    at dalvik.system.NativeStart.main(Native Method) 
05-11 15:11:41.773 18729-18729/com.monstartech.superuser.flashlight 

I/Process: Sending signal. PID: 18729 SIG: 9 

Answer 1

あなたのLogcatによると、このアプリは、それがこのラインであるように見えるれ、ライン173でクラッシュしている：

params = camera.getParameters(); 

だからあなたのカメラ変数は、おそらくnullです。ヌルカメラを確認してください。おそらく、ライン137から同じロジックを使用してカメラを初期化することができます。

private void setFlashLightOn() { 
    if (camera == null) { 
     // make isCameraFlash a class level variable 
     if(!isCameraFlash) { 
      showNoCameraAlert(); 
     } else { 
      camera = Camera.open(); 
      params = camera.getParameters(); 
     } 
    } 

    params = camera.getParameters(); 
    // etc 

Answer 2

あなたはカメラonStopをヌル・アウトが、カメラオブジェクトonStartを再作成されていません。私はカメラをキャンセルするだけですが、ヌルにしないでくださいonStop。

onStopあなたのアプリが破壊されたわけではありません。この場合、ヌルのカメラオブジェクトを使用して、そのままにして再開されます。