空指针异常 - 图像捕捉

Question

我是初学者。不知道我搞乱了什么。所以，任何帮助非常感谢。 第二项活动有一个意图打开第三项活动的按钮。第三项活动应开始使用相机功能打开，并在显示之前等待拍摄图像。然而，第三项活动一开始就失败了。 所以这里是代码。

Java代码（第2活动）。

public class CameraView extends Activity { 

public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    setContentView(R.layout.activity_camera_view); 
    // Show the Up button in the action bar. 
} 

public void onClickCam(View view) { 
    Intent intent = new Intent(this, ResultActivity.class); 
    startActivity(intent); 
} 



@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    switch (item.getItemId()) { 
    case android.R.id.home: 
     // This ID represents the Home or Up button. In the case of this 
     // activity, the Up button is shown. Use NavUtils to allow users 
     // to navigate up one level in the application structure. For 
     // more details, see the Navigation pattern on Android Design: 
     // 
     // http://developer.android.com/design/patterns/navigation.html#up-vs-back 
     // 
     NavUtils.navigateUpFromSameTask(this); 
     return true; 
    } 
    return super.onOptionsItemSelected(item); 
} 

} 

Java代码（第3活动）。

public class ResultActivity extends Activity { 

private static final int ACTION_TAKE_PHOTO_B = 1; 
private static final String BITMAP_STORAGE_KEY = "viewbitmap"; 
private static final String IMAGEVIEW_VISIBILITY_STORAGE_KEY = "imageviewvisibility"; 
private ImageView mImageView; 
private Bitmap mImageBitmap; 
private String mCurrentPhotoPath; 
private static final String JPEG_FILE_PREFIX = "IMG_"; 
private static final String JPEG_FILE_SUFFIX = ".jpg"; 
private AlbumStorageDirFactory mAlbumStorageDirFactory = null; 

/* Photo album for this application */ 
private String getAlbumName() { 
    return getString(R.string.album_name); 
} 

private File getAlbumDir() { 
    File storageDir = null; 

    if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) { 

     storageDir = mAlbumStorageDirFactory.getAlbumStorageDir(getAlbumName()); 

     if (storageDir != null) { 
      if (! storageDir.mkdirs()) { 
       if (! storageDir.exists()){ 
        Log.d("CameraSample", "failed to create directory"); 
        return null; 
       } 
      } 
     } 

    } else { 
     Log.v(getString(R.string.app_name), "External storage is not mounted READ/WRITE."); 
    } 

    return storageDir; 
} 

private File createImageFile() throws IOException { 
    // Create an image file name 
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date()); 
    String imageFileName = JPEG_FILE_PREFIX + timeStamp + "_"; 
    File albumF = getAlbumDir(); 
    File imageF = File.createTempFile(imageFileName, JPEG_FILE_SUFFIX, albumF); 
    return imageF; 
} 

private File setUpPhotoFile() throws IOException { 

    File f = createImageFile(); 
    mCurrentPhotoPath = f.getAbsolutePath(); 

    return f; 
} 

private void setPic() { 

    /* There isn't enough memory to open up more than a couple camera photos */ 
    /* So pre-scale the target bitmap into which the file is decoded */ 

    /* Get the size of the ImageView */ 
    int targetW = mImageView.getWidth(); 
    int targetH = mImageView.getHeight(); 

    /* Get the size of the image */ 
    BitmapFactory.Options bmOptions = new BitmapFactory.Options(); 
    bmOptions.inJustDecodeBounds = true; 
    BitmapFactory.decodeFile(mCurrentPhotoPath, bmOptions); 
    int photoW = bmOptions.outWidth; 
    int photoH = bmOptions.outHeight; 

    /* Figure out which way needs to be reduced less */ 
    int scaleFactor = 1; 
    if ((targetW > 0) || (targetH > 0)) { 
     scaleFactor = Math.min(photoW/targetW, photoH/targetH); 
    } 

    /* Set bitmap options to scale the image decode target */ 
    bmOptions.inJustDecodeBounds = false; 
    bmOptions.inSampleSize = scaleFactor; 
    bmOptions.inPurgeable = true; 

    /* Decode the JPEG file into a Bitmap */ 
    Bitmap bitmap = BitmapFactory.decodeFile(mCurrentPhotoPath, bmOptions); 

    /* Associate the Bitmap to the ImageView */ 
    mImageView.setImageBitmap(bitmap); 
    mImageView.setVisibility(View.VISIBLE); 
} 

private void galleryAddPic() { 
    Intent mediaScanIntent = new Intent("android.intent.action.MEDIA_SCANNER_SCAN_FILE"); 
    File f = new File(mCurrentPhotoPath); 
    Uri contentUri = Uri.fromFile(f); 
    mediaScanIntent.setData(contentUri); 
    this.sendBroadcast(mediaScanIntent); 
} 


private void dispatchTakePictureIntent(int actionCode) { 

    Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); 

    switch(actionCode) { 
    case ACTION_TAKE_PHOTO_B: 
     File f = null; 

     try { 
      f = setUpPhotoFile(); 
      mCurrentPhotoPath = f.getAbsolutePath(); 
      takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(f)); 
     } catch (IOException e) { 
      e.printStackTrace(); 
      f = null; 
      mCurrentPhotoPath = null; 
     } 
     break; 

    default: 
     break;   
    } // switch 

    startActivityForResult(takePictureIntent, actionCode); 
} 

private void handleBigCameraPhoto() { 

    if (mCurrentPhotoPath != null) { 
     setPic(); 
     galleryAddPic(); 
     mCurrentPhotoPath = null; 
    } 

} 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_result); 

    mImageView = (ImageView) findViewById(R.id.imageView1); 
    mImageBitmap = null; 

    Intent intent = new Intent(this, ResultActivity.class); 
    dispatchTakePictureIntent(ACTION_TAKE_PHOTO_B); 
    startActivity(intent); 

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.FROYO) { 
     mAlbumStorageDirFactory = new FroyoAlbumDirFactory(); 
    } else { 
     mAlbumStorageDirFactory = new BaseAlbumDirFactory(); 
    } 
} 

@Override 
protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
    switch (requestCode) { 
    case ACTION_TAKE_PHOTO_B: { 
     if (resultCode == RESULT_OK) { 
      handleBigCameraPhoto(); 
     } 
     break; 
    } // ACTION_TAKE_PHOTO_B 
    } // switch 
} 


// Some lifecycle callbacks so that the image can survive orientation change 
    @Override 
    protected void onSaveInstanceState(Bundle outState) { 
     outState.putParcelable(BITMAP_STORAGE_KEY, mImageBitmap); 
     outState.putBoolean(IMAGEVIEW_VISIBILITY_STORAGE_KEY, (mImageBitmap != null)); 
     super.onSaveInstanceState(outState); 
    } 

    @Override 
    protected void onRestoreInstanceState(Bundle savedInstanceState) { 
     super.onRestoreInstanceState(savedInstanceState); 
     mImageBitmap = savedInstanceState.getParcelable(BITMAP_STORAGE_KEY); 
     mImageView.setImageBitmap(mImageBitmap); 
     mImageView.setVisibility(
       savedInstanceState.getBoolean(IMAGEVIEW_VISIBILITY_STORAGE_KEY) ? 
         ImageView.VISIBLE : ImageView.INVISIBLE 
     ); 

    } 


/** 
* Indicates whether the specified action can be used as an intent. This 
* method queries the package manager for installed packages that can 
* respond to an intent with the specified action. If no suitable package is 
* found, this method returns false. 
* http://android-developers.blogspot.com/2009/01/can-i-use-this-intent.html 
* 
* @param context The application's environment. 
* @param action The Intent action to check for availability. 
* 
* @return True if an Intent with the specified action can be sent and 
*   responded to, false otherwise. 
*/ 
public static boolean isIntentAvailable(Context context, String action) { 
    final PackageManager packageManager = context.getPackageManager(); 
    final Intent intent = new Intent(action); 
    List<ResolveInfo> list = 
     packageManager.queryIntentActivities(intent, 
       PackageManager.MATCH_DEFAULT_ONLY); 
    return list.size() > 0; 
} 

} 

XML代码。

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
tools:context=".ResultActivity" > 

<ImageView 
    android:id="@+id/imageView1" 
    android:layout_height="wrap_content" 
    android:layout_width="wrap_content" 
    android:visibility="visible" 
    android:layout_centerHorizontal="true" 
    android:layout_centerVertical="true" /> 

logcat的

08-26 01:45:55.845: E/AndroidRuntime(3471): FATAL EXCEPTION: main 
08-26 01:45:55.845: E/AndroidRuntime(3471): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.camoid/com.example.camoid.ResultActivity}: java.lang.NullPointerException 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at android.os.Handler.dispatchMessage(Handler.java:99) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at android.os.Looper.loop(Looper.java:137) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at android.app.ActivityThread.main(ActivityThread.java:5103) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at java.lang.reflect.Method.invokeNative(Native Method) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at java.lang.reflect.Method.invoke(Method.java:525) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
08-26 01:45:55.845: E/AndroidRuntime(3471):  at dalvik.system.NativeStart.main(Native Method) 
08-26 01:45:55.845: E/AndroidRuntime(3471): Caused by: java.lang.NullPointerException 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.getAlbumDir(ResultActivity.java:47) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.createImageFile(ResultActivity.java:69) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.setUpPhotoFile(ResultActivity.java:76) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.dispatchTakePictureIntent(ResultActivity.java:135) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.onCreate(ResultActivity.java:171) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at android.app.Activity.performCreate(Activity.java:5133) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175) 

Answer 1

dispatchTakePictureIntent(ACTION_TAKE_PHOTO_B); 
startActivity(intent); 

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.FROYO) { 
    mAlbumStorageDirFactory = new FroyoAlbumDirFactory(); 
} else { 
    mAlbumStorageDirFactory = new BaseAlbumDirFactory(); 
} 

这里dispatchTakePictureIntent()间接调用一个函数getAlbumDir()使用mAlbumStorageDirFactory其作为logcat的观察尚未初始化，：

08-26 01:45:55.845: E/AndroidRuntime(3471): Caused by: java.lang.NullPointerException 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.getAlbumDir(ResultActivity.java:47) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.createImageFile(ResultActivity.java:69) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.setUpPhotoFile(ResultActivity.java:76) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.dispatchTakePictureIntent(ResultActivity.java:135) 
08-26 02:33:57.415: E/AndroidRuntime(3730):  at com.example.camoid.ResultActivity.onCreate(ResultActivity.java:171) 

设置mAlbumStorageDirFactory调用dispatchTakePictureIntnet()之前。

Answer 2

一个完整的工作解决方案

final private int PICK_IMAGE = 1; 
    final private int CAPTURE_IMAGE = 2; 
private String imgPath; 

btnGallery.setOnClickListener(new OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       Intent intent = new Intent(); 
       intent.setType("image/*"); 
       intent.setAction(Intent.ACTION_GET_CONTENT); 
       startActivityForResult(Intent.createChooser(intent, ""), PICK_IMAGE); 

      } 
     }); 

     btnCapture.setOnClickListener(new OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       final Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); 
       intent.putExtra(MediaStore.EXTRA_OUTPUT, setImageUri()); 
       startActivityForResult(intent, CAPTURE_IMAGE); 
      } 
     }); 


public Uri setImageUri() { 
     // Store image in dcim 
     File file = new File(Environment.getExternalStorageDirectory() + "/DCIM/", "image" + new Date().getTime() + ".png"); 
     Uri imgUri = Uri.fromFile(file); 
     this.imgPath = file.getAbsolutePath(); 
     return imgUri; 
    } 


    public String getImagePath() { 
     return imgPath; 
    } 


@Override 
    protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
     if (resultCode != Activity.RESULT_CANCELED) { 
      if (requestCode == PICK_IMAGE) { 
       selectedImagePath = getAbsolutePath(data.getData()); 
       imgUser.setImageBitmap(decodeFile(selectedImagePath)); 
      } else if (requestCode == CAPTURE_IMAGE) { 
       selectedImagePath = getImagePath(); 
       imgUser.setImageBitmap(decodeFile(selectedImagePath)); 
      } else { 
       super.onActivityResult(requestCode, resultCode, data); 
      } 
     } 

    } 

public String getAbsolutePath(Uri uri) { 
     String[] projection = { MediaColumns.DATA }; 
     @SuppressWarnings("deprecation") 
     Cursor cursor = managedQuery(uri, projection, null, null, null); 
     if (cursor != null) { 
      int column_index = cursor.getColumnIndexOrThrow(MediaColumns.DATA); 
      cursor.moveToFirst(); 
      return cursor.getString(column_index); 
     } else 
      return null; 
    } 

public Bitmap decodeFile(String path) { 
     try { 
      // Decode image size 
      BitmapFactory.Options o = new BitmapFactory.Options(); 
      o.inJustDecodeBounds = true; 
      BitmapFactory.decodeFile(path, o); 
      // The new size we want to scale to 
      final int REQUIRED_SIZE = 70; 

      // Find the correct scale value. It should be the power of 2. 
      int scale = 1; 
      while (o.outWidth/scale/2 >= REQUIRED_SIZE && o.outHeight/scale/2 >= REQUIRED_SIZE) 
       scale *= 2; 

      // Decode with inSampleSize 
      BitmapFactory.Options o2 = new BitmapFactory.Options(); 
      o2.inSampleSize = scale; 
      return BitmapFactory.decodeFile(path, o2); 
     } catch (Throwable e) { 
      e.printStackTrace(); 
     } 
     return null; 

    } 

Answer 3

我看到两种可能性。或者你a）忘记在清单中声明你的第二个活动，或者b）你的意图开始第二个活动是不正确的。

如果）

你需要你的<application>标签内的下列

<activity 
    android:name=".ResultActivity" 
    android:label="@string/app_name" > 
</activity> 

如果B）

这是开始一个活动的一种方式：

startActivityForResult(new Intent(this, ResultActivity.class), 0);