android - 空指针异常-图像捕获

Question

我是初学者。不知道我哪里搞砸了。所以非常感谢任何帮助。第二个 Activity 有一个按钮，用于打开第三个 Activity 。第三个 Activity 应该开始打开相机功能，并在显示之前等待捕获图像。然而，第三个 Activity 一开始就失败了。所以这是代码。

Java 代码(第二个 Activity )。

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(第三个 Activity )。

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" />

日志猫

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();
}

此处 dispatchTakePictureIntent() 间接调用函数 getAlbumDir()，该函数使用尚未初始化的 mAlbumStorageDirFactory，如 logcat 中所见:

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)

在调用dispatchTakePictureIntnet()之前设置mAlbumStorageDirFactory。