Question

我使用了一个URI的ArrayList，以便能够遍历图像并每次更新单个ImageView。当我接近这样做时，我得到一个NullPointerException，并且我认为它与相机旋转我的屏幕（破坏活动）有关，当它出现以前提到的图片时。

使用onSaveInstanceState和onResume时会出现什么样？ -

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageURI(android.net.Uri)' on a null object reference
at plaidshorts.rafael.myapplication.Person1Screen$5.onClick(Person1Screen.java:124)
at android.view.View.performClick(View.java:5209)
at android.view.View$PerformClick.run(View.java:21174)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5477)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

第124行是：

mainView.setImageURI(happyList.get(0));

我的dispatchTakePictureIntent提示相机或图库两次（参见开头的循环）。然后，OnActivityResult获取URI并将其添加到happyList（在onCreate中实例化）。

private void dispatchTakePictureIntent() {
    pictureCounter = -1;
    for(int i = 0; i < 2; i++) {
        pictureCounter++;
        Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
            // Create the File where the photo should go
            File photoFile = null;
            try {
                photoFile = createImageFile();
                outputFileUri = Uri.fromFile(photoFile);
            } catch (IOException ex) {
                Log.w("error","IOException");
            }catch (NullPointerException nullEx) {
                Log.w("error","NullPointerException");
            }
            // Camera.
            final List<Intent> cameraIntents = new ArrayList<Intent>();
            final Intent captureIntent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
            final PackageManager packageManager = getPackageManager();
            final List<ResolveInfo> listCam = packageManager.queryIntentActivities(captureIntent, 0);
            for (ResolveInfo res : listCam) {
                final String packageName = res.activityInfo.packageName;
                final Intent intent = new Intent(captureIntent);
                intent.setComponent(new ComponentName(res.activityInfo.packageName, res.activityInfo.name));
                intent.setPackage(packageName);
                intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photoFile));
                cameraIntents.add(intent);
            }
            // Filesystem.
            final Intent galleryIntent = new Intent();
            galleryIntent.setType("image/*");
            galleryIntent.setAction(Intent.ACTION_GET_CONTENT);
            // Chooser of filesystem options.
            final Intent chooserIntent = Intent.createChooser(galleryIntent, "Select Source");
            // Add the camera options.
            chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS, cameraIntents.toArray(new Parcelable[cameraIntents.size()]));
            startActivityForResult(chooserIntent, REQUEST_TAKE_PHOTO);
        }
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (resultCode == RESULT_OK) {
            if (requestCode == REQUEST_TAKE_PHOTO) {
                final boolean isCamera;
                if (data == null) {
                    isCamera = true;
                } else {
                    final String action = data.getAction();
                    if (action == null) {
                        isCamera = false;
                    } else {
                        isCamera = action.equals(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
                    }
                }
                Uri selectedImageUri;
                if (isCamera) {
                    selectedImageUri = outputFileUri;
                } else {
                    selectedImageUri = data == null ? null : data.getData();
                }
               // mainView.setImageURI(selectedImageUri);
               // Log.d("Before adding", selectedImageUri.toString());
                happyList.add(selectedImageUri);
            }
        }
    }

Answer 1

ArrayList<URI> uris = ..
//inStop of your application
SharedPreference sp = context.getSharePreference("imagineThis",0);
SharedPreference.Editor ed = sp.edit();
byte i =0;
for(Uri u : uris){ i++;
   ed.put(String.valueOf(i), u.toString());}
ed.commit();
//in onrestart of your app
uris.clear();//provided is not null;
SharedPreference sp = context.getSharePreference("imagineThis",0);
SharedPreference.Editor ed = sp.edit();
for(String s : ((Map<String,String>)sp.getAll()).values()){
   uris.add(Uri.parse(s));
}
ed.clear();
ed.commit();

我认为你现在很好

Answer 2

嘿，您只需覆盖活动中的onRetainNonConfigurationInstance并返回您的arraylist对象，并在onCreate（）方法中检查您的对象是否为null，如果其null使用getLastNonConfigurationInstance（）来检索对象

//PseudoCode 
onRetainNonConfigurationInstance()  {

return arraylistObject;

}

oncreate(Bundle onSavedInstance){

if(arraylistObject == null){

arraylistObject = (cast properly)getLastNonConfigurationInstance();

}

}

这是最简单的一种，但建议使用片段来保存旋转状态

Answer 3

将您的数据存储在onSaveInstanceState（）

中

@Override
public void onSaveInstanceState (Bundle outState) {
    // TODO Auto-generated method stub
    super.onSaveInstanceState(outState);
    outState.putSerializable("array", arrayDetails);
}

将这些代码行放在活动的OnCreate（）方法中，以获取方向更改中的arrayList。

if (savedInstanceState != null) {
      arrayDetails = (ArrayList<yourListType>)savedInstanceState.getSerializable("array");
}

如何在屏幕旋转上保存ArrayList <uri>？

3 个答案: