的Android應用程序崩潰，無法理解的logcat找到爲什麼

Question

我有這樣的代碼中的主要活動：

package flash.light.pro; 

import android.os.Bundle; 
import android.app.Activity; 
import android.content.Context; 
import android.content.pm.PackageManager; 
import android.hardware.Camera; 
import android.graphics.Color; 
import android.hardware.Camera.Parameters; 
import android.util.Log; 
import android.view.View; 
import android.view.WindowManager; 
import android.widget.Button; 
import android.view.View.OnLongClickListener; 


public class MainActivity extends Activity { 
    private boolean isBlack = false; 
    private boolean isLedOn = false; 
    private boolean supportsCamera = true; 
    private Camera camera; 
    final Parameters p = camera.getParameters(); 
    protected void onStop() { 
     super.onStop(); 

     if (camera != null) { 
      camera.release(); 
     } 
    } 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     setContentView(R.layout.activity_main); 
     final Button screen = (Button) findViewById (R.id.screen); 
     Context context = this; 
     PackageManager pm = context.getPackageManager(); 

     isBlack = false; 
     setBrightness(255); 

     if (!pm.hasSystemFeature(PackageManager.FEATURE_CAMERA)) { 
      Log.e("err", "Device has no camera!"); 
      supportsCamera = false; 
     } 


     try{ 
      camera = Camera.open(); 
     } catch (Exception e){ 
      Log.e(getString(R.string.app_name), "failed to open Camera"); 
      e.printStackTrace(); 
     } 

     screen.setOnClickListener(new Button.OnClickListener(){ 
      public void onClick(View v) { 
       if (isBlack){ 
        screen.setBackgroundColor(Color.WHITE); 
        isBlack = false; 
        setBrightness(255); 
       } 
       else{ 
        screen.setBackgroundColor(Color.BLACK); 
        isBlack = true; 
        setBrightness(0); 
       } 
      } 
     }); 

     if(supportsCamera){ 
      screen.setOnLongClickListener(new OnLongClickListener() { 
       public boolean onLongClick(View v) { 
        if(isLedOn){ 
         p.setFlashMode(Parameters.FLASH_MODE_TORCH); 
         camera.setParameters(p); 
         camera.startPreview(); 
         return true; 
        } 
        else{ 
         p.setFlashMode(Parameters.FLASH_MODE_OFF); 
         camera.setParameters(p); 
         camera.stopPreview(); 
         return true; 
        } 
       } 
      }); 
     } 
    } 

    private void setBrightness(int brightness) { 
     WindowManager.LayoutParams layoutParams = getWindow().getAttributes(); 
     layoutParams.screenBrightness = brightness/100.0f; 
     getWindow().setAttributes(layoutParams); 
    } 
} 

這AndroidManifest.xml中的代碼：

<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="flash.light.pro" 
    android:versionCode="1" 
    android:versionName="1.0" > 

    <uses-permission android:name="android.permission.CAMERA" /> 
    <uses-feature android:name="android.hardware.camera" /> 

    <uses-sdk 
     android:minSdkVersion="8" 
     android:targetSdkVersion="15" /> 
    <permission android:name="android.permission.FLASHLIGHT" 
      android:permissionGroup="android.permission-group.HARDWARE_CONTROLS" 
      android:protectionLevel="normal" 
      android:label="string/permlab_flashlight"/> 

    <application 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name=".MainActivity" 
      android:label="@string/title_activity_main" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
    </application> 

這是LogCat日誌：

11-14 20:05:06.772: D/AndroidRuntime(380): >>>>>> AndroidRuntime START com.android.internal.os.RuntimeInit <<<<<< 
11-14 20:05:06.772: D/AndroidRuntime(380): CheckJNI is ON 
11-14 20:05:07.371: D/AndroidRuntime(380): Calling main entry com.android.commands.pm.Pm 
11-14 20:05:07.392: D/AndroidRuntime(380): Shutting down VM 
11-14 20:05:07.400: I/AndroidRuntime(380): NOTE: attach of thread 'Binder Thread #3' failed 
11-14 20:05:07.411: D/dalvikvm(380): GC_CONCURRENT freed 101K, 71% free 297K/1024K, external 0K/0K, paused 1ms+1ms 
11-14 20:05:07.411: D/dalvikvm(380): Debugger has detached; object registry had 1 entries 
11-14 20:05:07.830: D/AndroidRuntime(390): >>>>>> AndroidRuntime START com.android.internal.os.RuntimeInit <<<<<< 
11-14 20:05:07.830: D/AndroidRuntime(390): CheckJNI is ON 
11-14 20:05:08.390: D/AndroidRuntime(390): Calling main entry com.android.commands.am.Am 
11-14 20:05:08.420: I/ActivityManager(61): Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] 

flg=0x10000000 cmp=flash.light.pro/.MainActivity } from pid 390 
11-14 20:05:08.450: I/ActivityManager(61): Start proc flash.light.pro for activity flash.light.pro/.MainActivity: pid=398 uid=10040 gids={1006} 
11-14 20:05:08.480: D/AndroidRuntime(390): Shutting down VM 
11-14 20:05:08.490: D/dalvikvm(390): GC_CONCURRENT freed 102K, 69% free 319K/1024K, external 0K/0K, paused 1ms+3ms 
11-14 20:05:08.500: D/dalvikvm(390): Debugger has detached; object registry had 1 entries 
11-14 20:05:09.270: D/AndroidRuntime(398): Shutting down VM 
11-14 20:05:09.270: W/dalvikvm(398): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
11-14 20:05:09.330: E/AndroidRuntime(398): FATAL EXCEPTION: main 
11-14 20:05:09.330: E/AndroidRuntime(398): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo 

{flash.light.pro/flash.light.pro.MainActivity}: java.lang.NullPointerException 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.os.Handler.dispatchMessage(Handler.java:99) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.os.Looper.loop(Looper.java:123) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.app.ActivityThread.main(ActivityThread.java:3683) 
11-14 20:05:09.330: E/AndroidRuntime(398): at java.lang.reflect.Method.invokeNative(Native Method) 
11-14 20:05:09.330: E/AndroidRuntime(398): at java.lang.reflect.Method.invoke(Method.java:507) 
11-14 20:05:09.330: E/AndroidRuntime(398): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
11-14 20:05:09.330: E/AndroidRuntime(398): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
11-14 20:05:09.330: E/AndroidRuntime(398): at dalvik.system.NativeStart.main(Native Method) 
11-14 20:05:09.330: E/AndroidRuntime(398): Caused by: java.lang.NullPointerException 
11-14 20:05:09.330: E/AndroidRuntime(398): at flash.light.pro.MainActivity.<init>(MainActivity.java:22) 
11-14 20:05:09.330: E/AndroidRuntime(398): at java.lang.Class.newInstanceImpl(Native Method) 
11-14 20:05:09.330: E/AndroidRuntime(398): at java.lang.Class.newInstance(Class.java:1409) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 
11-14 20:05:09.330: E/AndroidRuntime(398): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561) 
11-14 20:05:09.330: E/AndroidRuntime(398): ... 11 more 
11-14 20:05:09.410: W/ActivityManager(61): Force finishing activity flash.light.pro/.MainActivity 
11-14 20:05:09.940: W/ActivityManager(61): Activity pause timeout for HistoryRecord{4060c450 flash.light.pro/.MainActivity} 
11-14 20:05:20.739: W/ActivityManager(61): Activity destroy timeout for HistoryRecord{4060c450 flash.light.pro/.MainActivity} 
11-14 20:06:00.031: I/dalvikvm(61): Jit: resizing JitTable from 1024 to 2048 
11-14 20:06:19.377: D/SntpClient(61): request time failed: java.net.SocketException: Address family not supported by protocol 
11-14 20:08:35.071: I/Process(398): Sending signal. PID: 398 SIG: 9 
11-14 20:08:35.081: I/ActivityManager(61): Process flash.light.pro (pid 398) has died. 
11-14 20:08:35.111: W/InputManagerService(61): Window already focused, ignoring focus gain of: com.android.internal.view.IInputMethodClient$Stub 

$Proxy@4051a740 

該應用程序在啓動時崩潰，沒有錯誤，日誌不明確。我能做些什麼來解決它。通過爲什麼該應用程序應該是某種FlashLight。謝謝您的幫助。

Answer 1

private Camera camera; 
final Parameters p = camera.getParameters(); 

camera尚未初始化

我能找到出通過在你的第22行看作爲logcat的輸出指示。 不要被logcat中的信息量所淹沒，通常會發現包名的第一個實例將指示問題出在哪裏。

編輯：作爲旁註，您的包名應該是反向域名順序。因此，舉例來說，如果您的應用程序名爲flashlightpro，並且您的域名是example.com，那麼您的軟件包名稱應該是com.example.flashlightpro。這不是必需的，但它是一個標準慣例。

編輯2：相機的聲明更改爲：Camera camera = Camera.open();

編輯3：拍照的Android文檔的交易，但步驟1，2，3，10是你的情況很重要：

Obtain an instance of Camera from open(int). 
Get existing (default) settings with getParameters(). 
If necessary, modify the returned Camera.Parameters object and call setParameters(Camera.Parameters). 
... 
Important: Call release() to release the camera for use by other applications. Applications should release the camera immediately in onPause() (and re-open()it in onResume()). 

http://developer.android.com/reference/android/hardware/Camera.html

Answer 2

您試圖訪問一些東西，是不是initiliazed，這就是爲什麼越來越空指針Exception.The日誌說清楚。

檢查您的活動第22行您嘗試訪問尚未啓動的照相機。

Caused by: java.lang.NullPointerException 
11-14 20:05:09.330: E/AndroidRuntime(398): at flash.light.pro.MainActivity.<init> (MainActivity.java:22)