Android Camera.takePicture（） - nullPointerException

Question

我有一種感覺，這是一個小小的錯誤。我試圖設置一個自定義相機，當我點擊捕捉按鈕時，我得到一個空指針。也許我的相機實例是空的？不知道爲什麼我跟着文件非常密切。在下面發佈代碼和錯誤，謝謝！

主要類：

public class CameraActivity extends Activity { 
    private Camera mCamera; 
    private CameraPreview mPreview; 
    private String TAG = "CameraActivity"; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     this.requestWindowFeature(Window.FEATURE_NO_TITLE); 
     setContentView(R.layout.camera_preview); 

     // Create an instance of Camera 
     mCamera = getCameraInstance(); 

     // Create our Preview view and set it as the content of our activity. 
     mPreview = new CameraPreview(this, mCamera); 
     FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview); 
     preview.addView(mPreview); 

     Button captureButton = (Button) findViewById(R.id.button_capture); 
     captureButton.setOnClickListener(
      new View.OnClickListener() { 
       @Override 
       public void onClick(View v) { 
        // get an image from the camera 
        mCamera.takePicture(null, null, mPicture); 
       } 
      } 
     ); 
    } 

    /** A safe way to get an instance of the Camera object. */ 
    public static Camera getCameraInstance(){ 
     Camera mCamera = null; 
     try { 
      mCamera = Camera.open(); // attempt to get a Camera instance 
     } 
     catch (Exception e){ 
      // Camera is not available (in use or does not exist) 
     } 
     return mCamera; // returns null if camera is unavailable 
    } 

    @Override 
    protected void onPause() { 
     super.onPause(); 
     if (mCamera != null){ 
      mCamera.release();  // release the camera for other applications 
      mCamera = null; 
     } 
    } 

    @Override 
    protected void onResume() { 
     super.onResume(); 
     mCamera = getCameraInstance(); 
    } 

    private PictureCallback mPicture = new PictureCallback() { 

     @Override 
     public void onPictureTaken(byte[] data, Camera camera) { 
      Log.d(TAG, "Attempting to store picture..."); 
      final int MEDIA_TYPE_IMAGE = 100; 
      File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE); 
      if (pictureFile == null){ 
       Log.d(TAG, "Error creating media file, check storage permissions"); 
       return; 
      } 

      try { 
       FileOutputStream fos = new FileOutputStream(pictureFile); 
       fos.write(data); 
       fos.close(); 
      } catch (FileNotFoundException e) { 
       Log.d(TAG, "File not found: " + e.getMessage()); 
      } catch (IOException e) { 
       Log.d(TAG, "Error accessing file: " + e.getMessage()); 
      } 
     } 
    }; 

貓日誌：

03-27 01:13:06.892: E/AndroidRuntime(8008): FATAL EXCEPTION: main 
03-27 01:13:06.892: E/AndroidRuntime(8008): java.lang.NullPointerException 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at com.justbaumdev.tagsense.CameraActivity$2.onClick(CameraActivity.java:47) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at android.view.View.performClick(View.java:4204) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at android.view.View$PerformClick.run(View.java:17355) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at android.os.Handler.handleCallback(Handler.java:725) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at android.os.Handler.dispatchMessage(Handler.java:92) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at android.os.Looper.loop(Looper.java:137) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at java.lang.reflect.Method.invokeNative(Native Method) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at java.lang.reflect.Method.invoke(Method.java:511) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
03-27 01:13:06.892: E/AndroidRuntime(8008):  at dalvik.system.NativeStart.main(Native Method) 

預覽類：

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback { 
    private SurfaceHolder mHolder; 
    private Camera mCamera; 
    private int cameraId = 0; 
    private Context mContext; 
    private String TAG = "CameraPreview"; 

    public CameraPreview(Context context, Camera camera) { 
     super(context); 
     mContext = context; 
     mCamera = camera; 

     //get notified if surface created/destroyed 
     mHolder = getHolder(); 
     mHolder.addCallback(this); 
    } 

    @Override 
    public void surfaceCreated(SurfaceHolder holder) { 
     // The Surface has been created, now tell the camera where to draw the preview. 
     //setCameraDisplayOrientation(mContext, mCamera, cameraId); 
     try { 
      mCamera.setPreviewDisplay(holder); 
      mCamera.startPreview(); 
     } catch (IOException e) { 
      Log.d(TAG, "Error setting camera preview: " + e.getMessage()); 
     } 
    } 

    @Override 
    public void surfaceDestroyed(SurfaceHolder holder) { 
     //Take care of this in cameraActivity 
//  mCamera.stopPreview(); 
//  mCamera.release(); 
    } 


    @Override 
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) { 
     if(mHolder.getSurface() == null) 
      return; 

     // stop preview before making changes 
     try { 
      mCamera.stopPreview(); 
     } catch (Exception e){ 
      // ignore: tried to stop a non-existent preview 
     } 

     //setCameraDisplayOrientation(mContext, mCamera, cameraId); 


     // start preview with new settings 
     try { 
      mCamera.setPreviewDisplay(mHolder); 
      mCamera.startPreview(); 
     } catch (Exception e){ 
      Log.d(TAG, "Error starting camera preview: " + e.getMessage()); 
     } 
    } 

清單：

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

    <uses-sdk 
     android:minSdkVersion="16" 
     android:targetSdkVersion="16" /> 

    <uses-permission android:name="android.permission.INTERNET" /> 
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 
    <uses-permission android:name="android.permission.CAMERA" /> 
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> 
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" /> 
    <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" /> 
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> 
    <uses-permission android:name="android.permission.NFC" /> 

    <uses-feature android:name="android.hardware.camera" /> 
    <uses-feature android:name="android.hardware.nfc" /> 
    <uses-feature android:name="android.hardware.wifi.direct" /> 

    <uses-permission android:name="android.permission.READ_PROFILE" /> 
    <uses-permission android:name="android.permission.READ_CONTACTS" /> 

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

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
     <activity android:name="com.justbaumdev.tagsense.NFC"> 
      <intent-filter> 
       <action android:name="android.nfc.action.NDEF_DISCOVERED" /> 

       <category android:name="android.intent.category.DEFAULT" /> 

       <data android:mimeType="application/com.justbaumdev.tagsense" /> 
      </intent-filter> 
     </activity> 
     <activity android:name="AlbumGallery"></activity> 
     <activity android:name="CameraActivity"></activity> 
    </application> 

</manifest> 

Answer 1

我發現至少有一個錯誤。 你調用getCameraInstance()在onCreate()和onResume()和onResume()被調用onCreate()，這導致兩個camera.open()沒有camera.release()後調用。你應該撥打camera.open()在onResume()。

http://developer.android.com/training/camera/cameradirect.html

Answer 2

內

public static Camera getCameraInstance() 

要初始化本地（方法）可變

Camera mCamera = null; 

不是類實例變量（你打算）

private Camera mCamera; 

變化來自行：

Camera mCamera = null; 

到

this.mCamera = null; 

注：getCameraInstance()不應該是一個靜態方法。