java - 相机 NullPointerException

Question

我正在研究 Android 相机教程，SDK 11。出于某种原因，我在 handleCameraPhoto() 中得到了一个空指针。我唯一看到的是“无法将结果 ResultInfo{who=null, request=100, result=-1, data=null} 传递给 Activity ”，但我无法弄清楚原因。

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

Activity :

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        // create Intent to take a picture and return control to the calling application
        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        fileUri = getOutputMediaFileUri(MEDIA_TYPE_IMAGE); // create a file to save the image
        intent.putExtra(MediaStore.EXTRA_OUTPUT, fileUri); // set the image file name

        ///Toast.makeText(this, "File Uri"+fileUri.toString(), Toast.LENGTH_LONG).show();
        // start the image capture Intent
        startActivityForResult(intent, CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE);

    }   
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE) {
            if (resultCode == RESULT_OK) {
                // Image captured and saved to fileUri specified in the Intent
                handleCameraPhoto(data);
            } else if (resultCode == RESULT_CANCELED) {
                // User cancelled the image capture
                finish();
            } else {
                // Image capture failed, advise user
                finish();
                Toast.makeText(this, "Image capture failed, quiting", Toast.LENGTH_LONG).show();
            }
        }
    }
    /**
     * 
     * @param intent
     */
    private void handleCameraPhoto(Intent data) {
        Toast.makeText(this, "Image saved to:\n" +
                data.getData(), Toast.LENGTH_LONG).show();
    }

    /** Create a file Uri for saving an image or video */
    private static Uri getOutputMediaFileUri(int type){
          return Uri.fromFile(getOutputMediaFile(type));
    }

    /** Create a File for saving an image or video */
    private static File getOutputMediaFile(int type){
        // To be safe, you should check that the SDCard is mounted
        // using Environment.getExternalStorageState() before doing this.

        File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
                  Environment.DIRECTORY_PICTURES), "Shindiggy");
        // This location works best if you want the created images to be shared
        // between applications and persist after your app has been uninstalled.

        // Create the storage directory if it does not exist
        if (! mediaStorageDir.exists()){
            if (! mediaStorageDir.mkdirs()){
                Log.d("Shindiggy", "failed to create directory");
                return null;
            }
        }

        // Create a media file name
        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
        File mediaFile;
        if (type == MEDIA_TYPE_IMAGE){
            mediaFile = new File(mediaStorageDir.getPath() + File.separator +
            "IMG_"+ timeStamp + ".jpg");
        } else {
            return null;
        }

        return mediaFile;
    }

错误猫

11-19 11:39:06.782: W/dalvikvm(7719): threadid=1: thread exiting with uncaught exception (group=0x41549700)
11-19 11:39:06.782: E/AndroidRuntime(7719): FATAL EXCEPTION: main
11-19 11:39:06.782: E/AndroidRuntime(7719): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=100, result=-1, data=null} to activity {com.shindiggy.shindiggy/com.shindiggy.shindiggy.CameraActivity}: java.lang.NullPointerException
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.app.ActivityThread.deliverResults(ActivityThread.java:3367)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.app.ActivityThread.handleSendResult(ActivityThread.java:3410)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.app.ActivityThread.access$1100(ActivityThread.java:141)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1304)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.os.Looper.loop(Looper.java:137)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.app.ActivityThread.main(ActivityThread.java:5103)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at java.lang.reflect.Method.invokeNative(Native Method)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at java.lang.reflect.Method.invoke(Method.java:525)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at dalvik.system.NativeStart.main(Native Method)
11-19 11:39:06.782: E/AndroidRuntime(7719): Caused by: java.lang.NullPointerException
11-19 11:39:06.782: E/AndroidRuntime(7719):     at com.shindiggy.shindiggy.CameraActivity.handleCameraPhoto(CameraActivity.java:68)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at com.shindiggy.shindiggy.CameraActivity.onActivityResult(CameraActivity.java:51)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.app.Activity.dispatchActivityResult(Activity.java:5322)
11-19 11:39:06.782: E/AndroidRuntime(7719):     at android.app.ActivityThread.deliverResults(ActivityThread.java:3363)
11-19 11:39:06.782: E/AndroidRuntime(7719):     ... 11 more

Answer 1

似乎 handleCameraPhoto(asdf) 是在您的代码中使用参数调用的(但您没有向我们展示这部分)，问题是对象 asdf 未分配 new。这意味着程序内存中没有物理对象。

所以当方法的指令被执行时，更具体地说是 data.getData()，崩溃发生了，因为名称 data 没有引用有效的对象在程序的内存中。

NullPointerException 错误发生在我们尝试访问未正确分配的对象的成员时。 确保在调用 handleCameraPhoto() 时分配对象。