相机.takePicture空指针异常

Question

当我尝试使用此代码拍照时，我总是得到NullPointerException。它总是在camera.takePicture失败。

我试着用谷歌搜索这个问题，但没有找到任何东西。如有任何帮助，不胜感激。

代码

import android.annotation.TargetApi;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.hardware.Camera.CameraInfo;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

@TargetApi(Build.VERSION_CODES.GINGERBREAD)
public class CameraService extends Activity {
final static String DEBUG_TAG = "MakePhotoActivity";
  private Camera camera;
  private int cameraId = 0;
  @TargetApi(Build.VERSION_CODES.GINGERBREAD)
@Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    // do we have a camera?
    if (!getPackageManager()
        .hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
      Toast.makeText(this, "No camera on this device", Toast.LENGTH_LONG)
          .show();
    } else {
      cameraId = findFrontFacingCamera();
      if (cameraId < 0) {
        Toast.makeText(this, "No front facing camera found.",
            Toast.LENGTH_LONG).show();
      } else {
        camera = Camera.open(cameraId);
      }
    }
  }
  public void onClick(View view) {
    camera.takePicture(null, null,
        new PhotoHandler(getApplicationContext()));
  }
  private int findFrontFacingCamera() {
    int cameraId = -1;
    // Search for the front facing camera
    int numberOfCameras = Camera.getNumberOfCameras();
    for (int i = 0; i < numberOfCameras; i++) {
      CameraInfo info = new CameraInfo();
      Camera.getCameraInfo(i, info);
      if (info.facing == CameraInfo.CAMERA_FACING_FRONT) {
        Log.d(DEBUG_TAG, "Camera found");
        cameraId = i;
        break;
      }
    }
    return cameraId;
  }
  @Override
  protected void onPause() {
    if (camera != null) {
      camera.release();
      camera = null;
    }
    super.onPause();
  }

}

PhotoHandler代码

import java.io.File;
import java.io.FileOutputStream;
import java.text.SimpleDateFormat;
import java.util.Date;
import android.content.Context;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.os.Environment;
import android.util.Log;
import android.widget.Toast;
public class PhotoHandler implements PictureCallback{
private final Context context;
  public PhotoHandler(Context context) {
    this.context = context;
  }
  @Override
  public void onPictureTaken(byte[] data, Camera camera) {
    File pictureFileDir = getDir();
    if (!pictureFileDir.exists() && !pictureFileDir.mkdirs()) {
      Log.d(CameraService.DEBUG_TAG, "Can't create directory to save image.");
      Toast.makeText(context, "Can't create directory to save image.",
          Toast.LENGTH_LONG).show();
      return;
    }
    SimpleDateFormat dateFormat = new SimpleDateFormat("yyyymmddhhmmss");
    String date = dateFormat.format(new Date());
    String photoFile = "Picture_" + date + ".jpg";
    String filename = pictureFileDir.getPath() + File.separator + photoFile;
    File pictureFile = new File(filename);
    try {
      FileOutputStream fos = new FileOutputStream(pictureFile);
      fos.write(data);
      fos.close();
      Toast.makeText(context, "New Image saved:" + photoFile,
          Toast.LENGTH_LONG).show();
    } catch (Exception error) {
      Log.d(CameraService.DEBUG_TAG, "File" + filename + "not saved: "
          + error.getMessage());
      Toast.makeText(context, "Image could not be saved.",
          Toast.LENGTH_LONG).show();
    }
  }
  private File getDir() {
    File sdDir = Environment
      .getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
    return new File(sdDir, "CameraAPIDemo");
  }
}

logcat输出

04-15 18:24:42.316: E/AndroidRuntime(23331): FATAL EXCEPTION: main
04-15 18:24:42.316: E/AndroidRuntime(23331): java.lang.IllegalStateException: Could not execute method of the activity
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.view.View$1.onClick(View.java:3599)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.view.View.performClick(View.java:4204)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.view.View$PerformClick.run(View.java:17355)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.os.Handler.handleCallback(Handler.java:725)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.os.Handler.dispatchMessage(Handler.java:92)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.os.Looper.loop(Looper.java:137)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.app.ActivityThread.main(ActivityThread.java:5041)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at java.lang.reflect.Method.invokeNative(Native Method)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at java.lang.reflect.Method.invoke(Method.java:511)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at dalvik.system.NativeStart.main(Native Method)
04-15 18:24:42.316: E/AndroidRuntime(23331): Caused by: java.lang.reflect.InvocationTargetException
04-15 18:24:42.316: E/AndroidRuntime(23331):    at java.lang.reflect.Method.invokeNative(Native Method)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at java.lang.reflect.Method.invoke(Method.java:511)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.view.View$1.onClick(View.java:3594)
04-15 18:24:42.316: E/AndroidRuntime(23331):    ... 11 more
04-15 18:24:42.316: E/AndroidRuntime(23331): Caused by: java.lang.RuntimeException: takePicture failed
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.hardware.Camera.native_takePicture(Native Method)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.hardware.Camera.takePicture(Camera.java:1095)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at android.hardware.Camera.takePicture(Camera.java:1040)
04-15 18:24:42.316: E/AndroidRuntime(23331):    at com.egnoita.ignoramus.CameraService.onClick(CameraService.java:50)
04-15 18:24:42.316: E/AndroidRuntime(23331):    ... 14 more

Answer 1

我认为camera在您的onClick()函数中为空，因为onCreate()中没有保证的路径来创建camera。

修改onClick()如下:

public void onClick(View view) {
    if(camera == null) {
        // Warn user that camera is not available via "Toast" or similar.
    } else {
        camera.takePicture(null, null,
            new PhotoHandler(getApplicationContext()));
    }
}

Answer 2

我在2.3和4.0之间遇到了同样的兼容性问题。这里我假设在调用takePicture()之前调用了startPreview()。

请参阅下面的代码，它适用于我的2.3和4.0设备。

PictureCallback mJpegCallback;
SurfaceView surfaceViewDummy;
Camera mCamera;
mCamera = Camera.open();
try {
    // Important here!!! If use below line under 2.3 works,
    // but not work on 4.0! Will always got 
    // java.lang.RuntimeException: takePicture failed
    // Under 4.0 must create a real SurfaceView object on the screen!
    //surfaceViewDummy = new SurfaceView(this);
    surfaceViewDummy = (SurfaceView) findViewById(R.id.surfaceView1);
    mCamera.setPreviewDisplay(surfaceViewDummy.getHolder());
    mCamera.startPreview();
} catch (Exception e) {
    Log.d("", "Start preview error " + e.toString());
}
mJpegCallback = new PictureCallback() {
    public void onPictureTaken(byte[] data, Camera camera) {
        Log.d("", "Got picture data");
        // Save the picture data by yourself
        // ...
    }
};
mCamera.takePicture(null, null, mJpegCallback);

Answer 3

您的应用程序是否允许使用相机?

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

Answer 4

尝试将此添加到您的manifest文件

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

这将告诉设备应用程序使用了摄像头了解更多信息http://developer.android.com/guide/topics/media/camera.html

Answer 5

我在我的应用程序中使用与您相同的代码，我的应用程序也用于抛出空指针异常:

照相机。

(getApplicationContext());

我认为这是由于相机获得空值引起的。为了避免出现这种异常，我在这行代码的前面加了一个检查符。所以onClick函数看起来像:

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(cameraId);
  }
  camera.takePicture(null, null,new PhotoHandler(getApplicationContext()));
}

Answer 6

自从你发布查询很长时间，但问题是，你必须在调用takePicture API之前开始预览，那就是

 public void onClick(View view) {
camera.startPreview(); //Add this line
camera.takePicture(null, null,
    new PhotoHandler(getApplicationContext()));
}

我也在使用相同的代码。还要注意的是，除非你有前置摄像头，否则这将不允许你点击照片。如果你只是想用相机硬件拍照，请检查后置摄像头而不是前置摄像头。

Answer 7

你说NullPointerException在调用takePicture，所以我猜错误是在调用本身，而不是在PhotoHandler。我们需要LogCat来验证。

我认为罪魁祸首是:new PhotoHandler(getApplicationContext()。您应该在调用takePicture之前创建PhotoHandler，并在takePicture函数中使用它的值。

PhotoHandler mPhotoHandler = null;
public void onClick (View view) {
    mPhotoHandler = new PhotoHandler(getApplicationContext());
    camera.takePicture(null, null, mPhotoHandler);
}