Question

在过去的两天里，我一直在尝试使用ViewModel来存储ArrayList。但是，每次访问ViewModel时，它都会初始化ArrayList，并删除其中存储的数据。

我试图在ViewModel中包括一些方法来控制ArrayList的初始化，但是并没有帮助。每次访问ViewModel时，它将ArrayList重置为“ null”。

为什么会这样？我该如何阻止呢？

ViewModel_Quiz.java

import android.arch.lifecycle.ViewModel;
import java.util.ArrayList;

public class ViewModel_Quiz extends ViewModel {

    ArrayList<String> checkboxStatus;

    public void sendCheckboxStatus(ArrayList<String> arrayList){
        checkboxStatus = arrayList;
    }

    public ArrayList<String> getCheckboxStatus(){
        return checkboxStatus;
    }
}

FragmentQuiz_Selection.java

import android.arch.lifecycle.ViewModelProviders;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CheckBox;
import android.widget.ImageView;
import android.support.constraint.Group;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collections;

public class FragmentQuiz_Selection extends Fragment implements View.OnClickListener{

private FloatingActionButton fab_start;
//Create member variable for Checkbox loops
private boolean mChecked;
//Create ArrayList for QuizSelection
private ArrayList<String> mQuizSelection = new ArrayList<>();
//Create boolean for Expand/Collapse
//boolean iv_group_instruments = false;
//Create View variable
private View mView;
//Variables for database
private SQLiteDatabase mInstrumentsDB;
private InstrumentsDbHelper instrumentsDb;
//This contains the same data as mQuizSelection. It's used to prepare the database and populate mTotalRows.
private String[] mQuizSelectionArray;
//This is used as part of quizPrep() to populate mTotalRows. This may note need to be a memberVariable.
private int mTotalRows;
//This contains the total number of columns for the user's selection.
private int mTotalColumns;
//This holds all of the column/row pairs for the quiz.
private ArrayList<String> mQuizList = new ArrayList<>();
//This variable is used to interface with MainActivity
private OnQuizStarted mCallback;
//This ArrayList holds the CheckBox status for restoring the user's state
private ArrayList<String> mCheckboxStatus = new ArrayList<>();

public static FragmentQuiz_Selection newInstance() {
    FragmentQuiz_Selection fragment = new FragmentQuiz_Selection();
    return fragment;
}

//Create an interface to communicate with MainActivity
public interface OnQuizStarted {
    void onQuizStarted (ArrayList<String> arrayList);
}
// Connect the interface to MainActivity

@Override
public void onAttach(Context context) {
    super.onAttach(context);

    // This makes sure that the container activity has implemented
    // the callback interface. If not, it throws an exception
    try {
        mCallback = (OnQuizStarted) context;
    } catch (ClassCastException e) {
        throw new ClassCastException(context.toString()
                + " must implement OnQuizStarted");
    }
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    //Store views in variable
    mView = inflater.inflate(R.layout.fragment_quiz_selection, container, false);

    // Set onClickListeners
    setOnClickListeners();

    //Ensure all Checkboxes are set to 'false'
    ViewGroup constraintLayout = (ViewGroup) mView.findViewById(R.id.quiz_menu_layout);
    loopCheckboxesFalse(constraintLayout);

    //Create onClickListener for 'start' FAButton
    fab_start.setOnClickListener(new View.OnClickListener() {
        //If you click the FAButton, start the Quiz
        @Override
        public void onClick(View view) {
            //Create variable for ConstraintLayout
            ViewGroup constraintLayout = (ViewGroup) mView.findViewById(R.id.quiz_menu_layout);
            quizStart(constraintLayout);
        }
    });

    return mView;
}

//Handle actions when the user is returning to the Fragment
@Override
public void onResume() {
    super.onResume();
    Log.i("LIFECYCLE CHANGE", "Quiz_Selection, onResume has been called!");
    //Get mCheckboxStatus from ViewModel
    ViewModel_Quiz viewmodel = ViewModelProviders.of(this).get(ViewModel_Quiz.class);
    if (viewmodel.getCheckboxStatus() != null && !(viewmodel.getCheckboxStatus().isEmpty())) {
        mCheckboxStatus = viewmodel.getCheckboxStatus();
        setCheckboxStatus(mCheckboxStatus);
    }
    //If mChecked is 'true,' show FAButton. If mChecked is 'false,' hide FAButton.
    ViewGroup layout = mView.findViewById(R.id.quiz_menu_layout);
    mChecked = loopCheckboxesBoolean(layout);
    fabButton(mChecked, fab_start);
}

//Handle actions when the user is leaving, but not necessarily destroying, the Fragment
@Override
public void onPause() {
    super.onPause();
    Log.i("LIFECYCLE CHANGE", "Quiz_Selection, onPause has been called!");
    mCheckboxStatus.clear();
    recordCheckboxStatus(mCheckboxStatus);
    //Send mCheckboxStatus to ViewModel
    ViewModel_Quiz viewmodel = ViewModelProviders.of(this).get(ViewModel_Quiz.class);
    viewmodel.sendCheckboxStatus(mCheckboxStatus);
}

@Override
public void onClick(View view) {
    if (view instanceof CheckBox) {
        onCheckboxClicked(view);
    } else if (view instanceof ImageView) {
        onExpandCollapse(view);
    }
}

//METHOD:   Set Checkbox status for 'onCreate'
private void setCheckboxStatus (ArrayList<String> arrayList) {
    ViewGroup layout = mView.findViewById(R.id.quiz_menu_layout);
    int childCount = layout.getChildCount();
    //Iterate through the layout's CheckBox views
    for (int i = 0; i < childCount; i++) {
        View view = layout.getChildAt(i);
        //If item is a Checkbox, assign it as true or false
        if (view instanceof CheckBox) {
            if (arrayList.get(0) == "y") {
                ((CheckBox) view).setChecked(true);
                arrayList.remove(0);
            } else if (arrayList.get(0) == "n") {
                ((CheckBox) view).setChecked(false);
                arrayList.remove(0);
            }
        }
    }
}

//METHOD:   Store Checkbox status for 'onPause'
private void recordCheckboxStatus (ArrayList<String> arrayList) {
    ViewGroup layout = mView.findViewById(R.id.quiz_menu_layout);
    int childCount = layout.getChildCount();
    //Iterate through the layout's views
    for (int i = 0; i < childCount; i++) {
        View view = layout.getChildAt(i);
        //If item is a Checkbox && Checkbox is 'checked,' add 'y' to the arrayList.
        if (view instanceof CheckBox && ((CheckBox) view).isChecked()) {
            arrayList.add("y");
        //Else if item is a Checkbox && Checkbox is 'not checked,' add 'n' to the arrayList.
        } else if (view instanceof CheckBox && !((CheckBox) view).isChecked()){
            arrayList.add("n");
        //Else if item is not a Checkbox, skip this view and move to the next one
        } else {}
    }
}

}

Answer 1

您必须在ViewModel中使用MutableLiveData。

import android.arch.lifecycle.ViewModel;
import java.util.ArrayList;

public class ViewModel_Quiz extends ViewModel {

    MutableLiveData<Arraylist<String>> checkboxStatus;

    public void sendCheckboxStatus(ArrayList<String> arrayList){
        checkboxStatus.postValue(arrayList);
    }

    public ArrayList<String> getCheckboxStatus(){
        return checkboxStatus;
    }
}

Android ViewModel不断初始化ArrayList

1 个答案: