首页 \ 问答 \ Android Studio：SQlite db ListView项目在startActivity上消失(Android Studio: SQlite db ListView items disappear on startActivity)

Android Studio：SQlite db ListView项目在startActivity上消失(Android Studio: SQlite db ListView items disappear on startActivity)

 我是Android Studio和应用创建的新手。 我跟随Johhny Mansons Youtube quide寻找新的应用程序，并大大扩展了工作。 
 

 我的问题是，退出应用程序会在新登录时从列表视图中删除项目。 
 

 当我实现登录功能时，我将LoginActivity更改为主页面，按照startActivity到达MainActivity.java登录后应用程序功能齐全.A可以提交图片和文本，保存到SQLite并显示在ListView选项卡中。 
 

 但是，每当我退出或退回，然后再次登录。 数据被擦除。 我相信这是因为startActivity重新执行MainActivity，这可能是创建一个新数据库并删除旧数据库。 但我不确定原因及其发生的原因。 在实现LoginActivity之前，应用程序会保留数据。 
 

 LoginActivity（登录页面） 
 

mLogin = (Button) findViewById(R.id.oButton);
    mLogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            User user = new User(dbHandlerUsers.getUserCount(), String.valueOf(mUsername.getText()), String.valueOf(mPassword.getText()), null);
            if (validUser(user)) {

                CurrentUser g = CurrentUser.getInstance();
                g.setCurrentUser(String.valueOf(mUsername.getText()));

                Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                startActivity(intent);
                return;
            }
            Toast.makeText(getApplicationContext(), "Wrong username or password", Toast.LENGTH_SHORT).show();
        }
    });

 

 MainActivity（功能处理问题） 
 

 populateList（）应该让myListView显示问题。 值得注意的是，我正在使用两个数据库，一个用于用户，一个用于提问。 
 

public class MainActivity extends ActionBarActivity {

private static final int EDIT = 0, DELETE = 1;

EditText questionTxt; //include picture too
ImageView questionImageImgView;
List<Question> Questions = new ArrayList<Question>();
List<Question> OtherQuestions = new ArrayList<Question>(); //Preparing for incoming data
ListView myListView;
ListView otherListView;
Uri imageUri = Uri.parse("android.resource://kaist624.projekt.kse624_projekt1"+R.drawable.no_user_logo);
DatabaseHandler dbHandler;
double myLongitude = 0.0d, myLatitude = 0.0d; //Later remove 0.0d
double qLongitude = 0.0d, qLatitude = 0.0d;
int longClickedItemIndex;
ArrayAdapter<Question> questionAdapter;

private float currentValue;
private long lastUpdate;

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

    dbHandler = new DatabaseHandler(getApplicationContext());

    questionTxt = (EditText) findViewById(R.id.txtQuestion);
    myListView = (ListView) findViewById(R.id.listView);
    otherListView = (ListView) findViewById(R.id.listView2);
    questionImageImgView = (ImageView) findViewById(R.id.imgQuestion);

    //This make our items in listView clickable on an event.
    registerForContextMenu(myListView);
    myListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
        @Override
        public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
            longClickedItemIndex = position; //Position tell where the item was clicked

            return false;
        }
    });

    TabHost tabHost = (TabHost) findViewById(R.id.tabHost);
    tabHost.setup();
    ...


    final Button addBtn = (Button) findViewById(R.id.btnAdd);
    addBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //Find the currently logged in user
            CurrentUser user = CurrentUser.getInstance();
            String currentUser=user.getCurrentUser();

            //Add question
            Question question = new Question(dbHandler.getQuestionsCount(), String.valueOf(questionTxt.getText()), qLongitude, qLatitude, imageUri, currentUser);
            dbHandler.createQuestion(question);
            Questions.add(question);
            questionAdapter.notifyDataSetChanged();
            Toast.makeText(getApplicationContext(), String.valueOf(questionTxt.getText()) + " has been added", Toast.LENGTH_SHORT).show();
            clearFields();
        }
    });

    questionTxt.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            addBtn.setEnabled(String.valueOf(questionTxt.getText()).trim().length() > 0);
        }

        @Override
        public void afterTextChanged(Editable s) {

        }
    });




    //Populate list view with questions
    if (dbHandler.getQuestionsCount() !=0)  //If there are contacts
        Questions.addAll(dbHandler.getAllQuestions()); //Add content

    populateList();

}

...

    dHandler.deleteQuestion(Questions.get(longClickedItemIndex));
            Questions.remove(longClickedItemIndex);
            questionAdapter.notifyDataSetChanged();
            break;
    }

    return super.onContextItemSelected(item);
}

public void onActivityResult(int reqCode, int resCode, Intent data) {
    if (resCode == RESULT_OK) {
        if (reqCode == 1) {
            imageUri = data.getData();
            questionImageImgView.setImageURI(data.getData());

        }
    }
}

private void populateList() {
    questionAdapter = new QuestionListAdapter();
    myListView.setAdapter(questionAdapter);
    //Add method to search for other phone's adapter list
    otherListView.setAdapter(questionAdapter);
}

private class QuestionListAdapter extends ArrayAdapter<Question> { //THIS CREATES A GROUP OF QUESTION, DISTANCE AND IMAGE - AS ONE OBJECT
    public QuestionListAdapter() {
        super (MainActivity.this, R.layout.listview_item, Questions);
    }
    @Override
    public View getView(int position, View view, ViewGroup parent) {
        if (view == null)
            view = getLayoutInflater().inflate(R.layout.listview_item, parent, false);

        Question currentQuestion = Questions.get(position);

        TextView question = (TextView) view.findViewById(R.id.qQuestion);
        question.setText(currentQuestion.getQuestion());
        TextView username = (TextView) view.findViewById(R.id.qLongitude);
        username.setText(currentQuestion.getUser());
        //TextView longitude = (TextView) view.findViewById(R.id.qLongitude);
        //longitude.setText(currentQuestion.getUser());
        TextView latitude = (TextView) view.findViewById(R.id.qLatitude);
        latitude.setText(Double.toString(currentQuestion.getLatitude()) + " meters");
        ImageView  questionImage = (ImageView) view.findViewById(R.id.qImageView);
        questionImage.setImageURI(currentQuestion.getImageURI());

        //TextView distance = (TextView) view.findViewById(R.id.qDistance);
        //distance.setText(Double.toString(currentQuestion.getDistance()));

        return view;
    }
}

 

 如果我应该提供更多信息，请告诉我。 
 

 类概述 - CurrentUser - DatabaseHandler - DatabaseHandlerUser - LoginActivity 
 - 主要活动 
 - 题 
 - RegisterActivity - 用户 

I am new to Android Studio and app creation. I followed Johhny Mansons Youtube quide for new apps, and extended the work greatly. 
 

My problem is, logging out of the app removes items from the list view, upon a new login. 
 

When I implemented login functionality, I changed LoginActivity to the main page, following a startActivity to reach MainActivity.java The app is fully functional once you log in. A can submit a picture and text, it is saved to SQLite and display in ListView tab. 
 

However, whenever I log out, or tab back, and login again. The data is wiped. I believe it is because the startActivity executes MainActivity anew, which could be creating a new database and removing the old. But I am not quite sure of the cause and why it happens. Before implmeneting LoginActivity, the app would retain the data fine.
 

LoginActivity (Login page)
 

mLogin = (Button) findViewById(R.id.oButton);
    mLogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            User user = new User(dbHandlerUsers.getUserCount(), String.valueOf(mUsername.getText()), String.valueOf(mPassword.getText()), null);
            if (validUser(user)) {

                CurrentUser g = CurrentUser.getInstance();
                g.setCurrentUser(String.valueOf(mUsername.getText()));

                Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                startActivity(intent);
                return;
            }
            Toast.makeText(getApplicationContext(), "Wrong username or password", Toast.LENGTH_SHORT).show();
        }
    });

 

MainActivity (Function handling questions)
 

It is the populateList() that should get myListView to display Questions. It might also be worth noting that I am using two databases, one for users and one for questions.
 

public class MainActivity extends ActionBarActivity {

private static final int EDIT = 0, DELETE = 1;

EditText questionTxt; //include picture too
ImageView questionImageImgView;
List<Question> Questions = new ArrayList<Question>();
List<Question> OtherQuestions = new ArrayList<Question>(); //Preparing for incoming data
ListView myListView;
ListView otherListView;
Uri imageUri = Uri.parse("android.resource://kaist624.projekt.kse624_projekt1"+R.drawable.no_user_logo);
DatabaseHandler dbHandler;
double myLongitude = 0.0d, myLatitude = 0.0d; //Later remove 0.0d
double qLongitude = 0.0d, qLatitude = 0.0d;
int longClickedItemIndex;
ArrayAdapter<Question> questionAdapter;

private float currentValue;
private long lastUpdate;

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

    dbHandler = new DatabaseHandler(getApplicationContext());

    questionTxt = (EditText) findViewById(R.id.txtQuestion);
    myListView = (ListView) findViewById(R.id.listView);
    otherListView = (ListView) findViewById(R.id.listView2);
    questionImageImgView = (ImageView) findViewById(R.id.imgQuestion);

    //This make our items in listView clickable on an event.
    registerForContextMenu(myListView);
    myListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
        @Override
        public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
            longClickedItemIndex = position; //Position tell where the item was clicked

            return false;
        }
    });

    TabHost tabHost = (TabHost) findViewById(R.id.tabHost);
    tabHost.setup();
    ...


    final Button addBtn = (Button) findViewById(R.id.btnAdd);
    addBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //Find the currently logged in user
            CurrentUser user = CurrentUser.getInstance();
            String currentUser=user.getCurrentUser();

            //Add question
            Question question = new Question(dbHandler.getQuestionsCount(), String.valueOf(questionTxt.getText()), qLongitude, qLatitude, imageUri, currentUser);
            dbHandler.createQuestion(question);
            Questions.add(question);
            questionAdapter.notifyDataSetChanged();
            Toast.makeText(getApplicationContext(), String.valueOf(questionTxt.getText()) + " has been added", Toast.LENGTH_SHORT).show();
            clearFields();
        }
    });

    questionTxt.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            addBtn.setEnabled(String.valueOf(questionTxt.getText()).trim().length() > 0);
        }

        @Override
        public void afterTextChanged(Editable s) {

        }
    });




    //Populate list view with questions
    if (dbHandler.getQuestionsCount() !=0)  //If there are contacts
        Questions.addAll(dbHandler.getAllQuestions()); //Add content

    populateList();

}

...

    dHandler.deleteQuestion(Questions.get(longClickedItemIndex));
            Questions.remove(longClickedItemIndex);
            questionAdapter.notifyDataSetChanged();
            break;
    }

    return super.onContextItemSelected(item);
}

public void onActivityResult(int reqCode, int resCode, Intent data) {
    if (resCode == RESULT_OK) {
        if (reqCode == 1) {
            imageUri = data.getData();
            questionImageImgView.setImageURI(data.getData());

        }
    }
}

private void populateList() {
    questionAdapter = new QuestionListAdapter();
    myListView.setAdapter(questionAdapter);
    //Add method to search for other phone's adapter list
    otherListView.setAdapter(questionAdapter);
}

private class QuestionListAdapter extends ArrayAdapter<Question> { //THIS CREATES A GROUP OF QUESTION, DISTANCE AND IMAGE - AS ONE OBJECT
    public QuestionListAdapter() {
        super (MainActivity.this, R.layout.listview_item, Questions);
    }
    @Override
    public View getView(int position, View view, ViewGroup parent) {
        if (view == null)
            view = getLayoutInflater().inflate(R.layout.listview_item, parent, false);

        Question currentQuestion = Questions.get(position);

        TextView question = (TextView) view.findViewById(R.id.qQuestion);
        question.setText(currentQuestion.getQuestion());
        TextView username = (TextView) view.findViewById(R.id.qLongitude);
        username.setText(currentQuestion.getUser());
        //TextView longitude = (TextView) view.findViewById(R.id.qLongitude);
        //longitude.setText(currentQuestion.getUser());
        TextView latitude = (TextView) view.findViewById(R.id.qLatitude);
        latitude.setText(Double.toString(currentQuestion.getLatitude()) + " meters");
        ImageView  questionImage = (ImageView) view.findViewById(R.id.qImageView);
        questionImage.setImageURI(currentQuestion.getImageURI());

        //TextView distance = (TextView) view.findViewById(R.id.qDistance);
        //distance.setText(Double.toString(currentQuestion.getDistance()));

        return view;
    }
}

 

Let me know if I should provide more information. 
 

Class overview - CurrentUser - DatabaseHandler - DatabaseHandlerUser - LoginActivity
 - MainActivity
 - Question
 - RegisterActivity - User 

原文：https://stackoverflow.com/questions/29945756
更新时间：2023-04-13 11:04

最满意答案

 创建一个表单 ，每个图像都有一个复选框。 
 

 使用图片ID作为复选框的ID。 
 

 如果表单已提交且有效，则会对图像进行迭代以了解其复选框是否已选中： 
 

use Symfony\Component\HttpFoundation\Request;

use Symfony\Component\Form\Extension\Core\Type\CheckboxType;
use Symfony\Component\Form\Extension\Core\Type\SubmitType;

public function deleteImagesAction(Request $request){

    // ...

    $images = // ...

    $formBuilder = $this->createFormBuilder();

    foreach($images as $image){
        $formBuilder->add($image->getId(),CheckboxType::class,array('label'=>$image->getName(),'required'=>false));
    }

    $formBuilder->add('submit',SubmitType::class);

    $form = $formBuilder->getForm();

    $form->handleRequest($request);

    if($form->isValid()){
        $data = $form->getData();

        $em = $this->getDoctrine()->getEntityManager();

        foreach($images as $image){
            if($data[$image->getId()]){
                $em->remove($image);
            }
        }

        $em->flush();

        return $this->redirectToRoute(...);
    }

    return $this->render(...);
}


Create a Form, with a checkbox for each image.
 

Use the image id as id for the checkbox.
 

If the form is submitted and valid iterate over the images to know if their checkboxes were checked or not :
 

use Symfony\Component\HttpFoundation\Request;

use Symfony\Component\Form\Extension\Core\Type\CheckboxType;
use Symfony\Component\Form\Extension\Core\Type\SubmitType;

public function deleteImagesAction(Request $request){

    // ...

    $images = // ...

    $formBuilder = $this->createFormBuilder();

    foreach($images as $image){
        $formBuilder->add($image->getId(),CheckboxType::class,array('label'=>$image->getName(),'required'=>false));
    }

    $formBuilder->add('submit',SubmitType::class);

    $form = $formBuilder->getForm();

    $form->handleRequest($request);

    if($form->isValid()){
        $data = $form->getData();

        $em = $this->getDoctrine()->getEntityManager();

        foreach($images as $image){
            if($data[$image->getId()]){
                $em->remove($image);
            }
        }

        $em->flush();

        return $this->redirectToRoute(...);
    }

    return $this->render(...);
}

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