camera.takePicture空指针异常(camera.takePicture null po

2019-11-02 01:17发布

站内文章 / 前端开发
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我总是一个NullPointerException当我尝试使用此代码拍照。 它总是失败的camera.takePicture。

我试图谷歌这个问题，并没有发现任何东西。 任何帮助，将不胜感激。

下面是代码

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();
  }

}

代码PhotoHandler 

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");
  }
}

该logcat的输出

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:

我得到了2.3和4.0之间的相同的兼容性问题。 在这里，我假设你叫startPreview()调用之前takePicture()

请参阅我下面的代码，它为我的作品都2.3和4.0的设备。 

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 2:

我认为camera是在你空onClick()函数，因为在没有保证路径onCreate()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 3:

难道你的应用程序许可使用的相机？ 

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


Answer 4:

尝试添加到您的清单文件

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

这将告诉该应用程序使用相机欲了解更多信息的设备http://developer.android.com/guide/topics/media/camera.html



Answer 5:

我使用相同的代码，你在我的应用程序和我的应用程序也用完就扔就行了空指针异常：

camera.takePicture（NULL，NULL，新PhotoHandler（getApplicationContext（）））;

我认为，这是由于摄像机引起越来越空value.To避免这种例外，我把支票在这条线code.So的了的onClick函数看起来像的顶部： 

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()));
}

希望能帮助到你 ！



Answer 6:

因为您发布的查询，但问题是，你必须调用API takePicture之前开始预览很长一段时间，也就是

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

我也是使用相同的代码。 还要注意的是，除非你有一个前置摄像头，这不会让你点击一个图片。 如果你只是想使用摄像头硬件拍摄照片，检查是否有后置摄像头，而不是前置摄像头。



Answer 7:

你说NullPointerException上调用takePicture ，所以我的猜测错误是在调用本身，而不是在PhotoHandler 。 我们需要LogCat验证。

我认为罪魁祸首是： new PhotoHandler(getApplicationContext()您应该创建PhotoHandler之前调用takePicture ，并在使用它的价值takePicture功能。 

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


文章来源: camera.takePicture null pointer exception
标签： android android-camera
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