获得NullPointerException异常在我定制的Andr​​oid摄像头应用程序

问题描述

我想打造的Andr​​oid我第一个自定义的相机应用。

I'm trying to build my first custom camera-app in Android.

在模拟器我得到：

不幸的是，[应用程序名称]已经停止了

"Unfortunately, [app name] has stopped"

这是错误日志：（如果你要我贴的完全的日志，请说出来）

This is the error log: (if you want me to paste the full log, please say so)

11-13 19:14:04.023: E/AndroidRuntime(4474): FATAL EXCEPTION: main
11-13 19:14:04.023: E/AndroidRuntime(4474): java.lang.NullPointerException
11-13 19:14:04.023: E/AndroidRuntime(4474):     at com.kachingcamapp.CameraApplication.surfaceChanged(CameraApplication.java:80)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.SurfaceView.updateWindow(SurfaceView.java:554)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.SurfaceView.access$000(SurfaceView.java:81)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:169)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:671)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1818)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.Choreographer.doCallbacks(Choreographer.java:555)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.Choreographer.doFrame(Choreographer.java:525)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.os.Handler.handleCallback(Handler.java:615)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.os.Handler.dispatchMessage(Handler.java:92)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.os.Looper.loop(Looper.java:137)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at android.app.ActivityThread.main(ActivityThread.java:4745)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at java.lang.reflect.Method.invokeNative(Native Method)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at java.lang.reflect.Method.invoke(Method.java:511)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-13 19:14:04.023: E/AndroidRuntime(4474):     at dalvik.system.NativeStart.main(Native Method)

这里是我的code：

public class CameraApplication extends Activity implements OnClickListener,
                            SurfaceHolder.Callback, Camera.PictureCallback {

    private static final String TAG = "AppDebug";
    SurfaceView cameraView;
    SurfaceHolder surfaceHolder;
    Camera camera;

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

        setContentView(R.layout.cam_view);

        cameraView = (SurfaceView) this.findViewById(R.id.CameraView);

        surfaceHolder = cameraView.getHolder();
        surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
        surfaceHolder.addCallback(this);

        cameraView.setFocusable(true);
        cameraView.setFocusableInTouchMode(true);
        cameraView.setClickable(true);

        cameraView.setOnClickListener(this);
        Log.d(TAG,"before calling surfaceCreated");
        surfaceCreated(surfaceHolder);
        Log.d(TAG,"end of onCreate");
    }

    public void onClick(View v) {
        camera.takePicture(null, null, this);
    }

    public void onPictureTaken(byte[] data, Camera camera) {
       Uri imageFileUri =
          getContentResolver().insert(Media.EXTERNAL_CONTENT_URI, new ContentValues());
        try {
              OutputStream imageFileOS =
                       getContentResolver().openOutputStream(imageFileUri);
            imageFileOS.write(data);
            imageFileOS.flush();
            imageFileOS.close();
        } catch (FileNotFoundException e) {
            Toast t = Toast.makeText(this,e.getMessage(), Toast.LENGTH_SHORT);
            t.show();
        } catch (IOException e) {
            Toast t = Toast.makeText(this,e.getMessage(), Toast.LENGTH_SHORT);
            t.show();
        }
        camera.startPreview();
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        camera.startPreview();
    }

    public void surfaceCreated(SurfaceHolder holder) {
        camera = Camera.open();

        try {
            if(camera==null){
                throw new Exception("camera is null");
            }
            camera.setPreviewDisplay(holder);
   }
        catch (IOException exception)
        {
                      camera.release();
                      Log.d(TAG,exception.toString());
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
           camera.stopPreview();
        camera.release();
    }
} // End the Activity

和这里的Andr​​oidManifest XML：

And here's the AndroidManifest XML:

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

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

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

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

</manifest>

现在我知道，从上面的问题出在 surfaceChanged 方法，是precise，在 camera.start preVIEW 这是code在方法中唯一的一块。

Now I know that from above the problem lies in the surfaceChanged method, to be precise, the camera.startPreview which is the only piece of code in the method.

但我真的没有看到任何破损或错。东西肯定是空，但我不知道是什么。

But I really don't see anything broken or wrong with it. Something definitely is null, but I don't know what.

推荐答案

您说你混得错误：

public void onClick(View v) {
  camera.takePicture(null, null, this);
}

在您comments.I之一，因为相机是在有一个空值也有这种issue.Thats的moment.Modify您code如下：

in one of your comments.I too had this issue.Thats because the camera is having a null value at that moment.Modify your code as below:

public void onClick(View view) {
  if (camera != null) {
    Log.d("camera state","camera is NOT null");
  }else{
    Log.d("camera state","camera is null");
    camera = android.hardware.Camera.open();
}
  camera.takePicture(null, null,new PhotoHandler(getApplicationContext()));
}

PS：我曾在我的应用程序的PhotoHandler类，修改该按您的req.Hope它有助于

PS: I had the PhotoHandler class in my app,modify this as per your req.Hope it helps !

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