Android相机示例空指针异常

我想从Android website实现相机SDK示例代码，但是当我尝试运行该应用程序时，我得到这个空指针异常和logcat并没有真正给我一大堆信息去上。我对Android开发很新，所以我不知道如何继续调试这个问题。Android相机示例空指针异常

06-07 09:48:24.960  927-927/com.luketim.cam.cam2.app E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    Process: com.luketim.cam.cam2.app, PID: 927 
    java.lang.NullPointerException 
      at com.luketim.cam.cam2.app.CameraPreview.surfaceCreated(CameraPreview.java:34) 
      at android.view.SurfaceView.updateWindow(SurfaceView.java:572) 
      at android.view.SurfaceView.access$000(SurfaceView.java:86) 
      at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:175) 
      at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:847) 
      at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1871) 
      at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000) 
      at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670) 
      at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761) 
      at android.view.Choreographer.doCallbacks(Choreographer.java:574) 
      at android.view.Choreographer.doFrame(Choreographer.java:544) 
      at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747) 
      at android.os.Handler.handleCallback(Handler.java:733) 
      at android.os.Handler.dispatchMessage(Handler.java:95) 
      at android.os.Looper.loop(Looper.java:136) 
      at android.app.ActivityThread.main(ActivityThread.java:5017) 
      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:779) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
      at dalvik.system.NativeStart.main(Native Method)

以下是引发此NullPointerException的方法的类。

package com.luketim.cam.cam2.app; 

import android.content.Context; 
import android.hardware.Camera; 
import android.util.Log; 
import android.view.SurfaceHolder; 
import android.view.SurfaceView; 

import java.io.IOException; 

/** 
* Created by luketimothy on 06/06/2014. 
*/ 
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback { 
    private static final String TAG = ""; 
    private SurfaceHolder mHolder; 
    private Camera mCamera; 

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

     // Install a SurfaceHolder.Callback so we get notified when the 
     // underlying surface is created and destroyed. 
     mHolder = getHolder(); 
     mHolder.addCallback(this); 
     // deprecated setting, but required on Android versions prior to 3.0 
     mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); 
    } 

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

    public void surfaceDestroyed(SurfaceHolder holder) { 
     // empty. Take care of releasing the Camera preview in your activity. 
    } 

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { 
     // If your preview can change or rotate, take care of those events here. 
     // Make sure to stop the preview before resizing or reformatting it. 

     if (mHolder.getSurface() == null){ 
      // preview surface does not exist 
      return; 
     } 

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

     // set preview size and make any resize, rotate or 
     // reformatting changes here 

     // start preview with new settings 
     try { 
      mCamera.setPreviewDisplay(mHolder); 
      mCamera.startPreview(); 

     } catch (Exception e){ 
      Log.d(TAG, "Error starting camera preview: " + e.getMessage()); 
     } 
    } 
}

来源

2014-06-07 Luke

logcat中并没有真正给我一大堆信息中去

它会告诉你对你崩溃代码行（CameraPreview.java:34，在你surfaceCreated()法）为什么你坠毁（一NullPointerException occurred on that line)。

由于只有两行surfaceCreated()，很显然，mCamera是null。因为这是从代码个外部在您列出的位置上，您需要跟踪您打开相机的位置，并确定为何无法按预期工作。在Android中编写摄像头应用程序是一件很困难的事情。这不是一个新的Android应该尝试的东西。我提供a library来尝试简化在应用内使用相机，但即使这样也不能处理设备制造商所做的任何奇怪的事情。

来源

2014-06-07 14:08:24 CommonsWare

我并不是Java的新手，但自从我上次使用它之后已经过了几年了。不知何故，我设法错过了那里的行号！不过，我对Android很陌生。我会检查你的图书馆，它应该对像我这样的人有很大的帮助。谢谢！ – Luke

@Luke：对不起。通常，如果有人难以解释堆栈跟踪，他们是Java的新手。我从我的回答中找到了这个参考。 – CommonsWare

Android相机示例空指针异常

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