不使用 SharedPreferences 将项目添加到列表中？

Question

我正在尝试制作一个应用程序，您可以在其中使用 EditText 和 ListView 将项目添加到列表中。它必须记住您添加到列表中的内容，因为有多个活动，所以我使用 SharedPreferences。活动第一次打开时它崩溃了，因为它查找了一个 SharedPreferences 文件但它不存在，所以我添加了

if (newquestion == null) {
        return;
    }

但现在它从不向列表中添加任何内容。

此活动的完整代码：

package com.example.dogwise;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.AdapterView;
import android.content.SharedPreferences;

public class Questions extends AppCompatActivity {
    ListView listview;
    String[] ListElements = new String[]{
            "How much food should I feed my dog?",
            "How do I teach my dog to sit?"
    };

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

        listview = (ListView) findViewById(R.id.QuestionsList);

        final List<String> ListElementsArrayList = new ArrayList<String>(Arrays.asList(ListElements));
        final ArrayAdapter<String> adapter = new ArrayAdapter<String>
                (Questions.this, android.R.layout.simple_list_item_1, ListElementsArrayList);
        listview.setAdapter(adapter);
        adapter.notifyDataSetChanged();

        SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", MODE_PRIVATE);
        String newquestion=pref.getString("key_question", null);

        if (newquestion == null) {
            return;
        }

        ListElementsArrayList.add(newquestion);
        adapter.notifyDataSetChanged();

        Bundle newQuestion = getIntent().getExtras();
        if (newQuestion == null) {
            return;
        }
        final String QuestionName = newQuestion.getString("QuestionName");

        ListElementsArrayList.add(QuestionName);
        adapter.notifyDataSetChanged();

        SharedPreferences.Editor editor = getSharedPreferences("MyPref", MODE_PRIVATE).edit();
        editor.putString("key_question", QuestionName);

        editor.apply();

        listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                if (position == 0) {
                    Intent myIntent = new Intent(view.getContext(), Question_1.class);
                    startActivityForResult(myIntent, 0);
                }

                if (position == 1) {
                    Intent myIntent = new Intent(view.getContext(), Question_2.class);
                    startActivityForResult(myIntent, 0 );
                }

                if (position == 2) {
                    Intent myIntent = new Intent(view.getContext(), Question_Asked.class);
                    myIntent.putExtra("QuestionTitle", QuestionName);
                    startActivityForResult(myIntent, 0);
                }
            }
        });
    }

    ;

    public void backHomeOnClick(View view) {
        Intent b = new Intent(this, HomeScreen.class);
        startActivity(b);
    }

    public void askAQuestionOnClick(View view) {
        Intent i = new Intent(this, AskAQuestion.class);
        startActivity(i);
    }

    ;
}

Answer 1

您正在使用 key="QuestionTitle" 将数据发布到 Intent 中，但尝试使用 key="QuestionName" 检索该数据。