将listView数据从一个活动发送到另一个活动

Question

我试图找出如何从listView获取数据，将其存储在一个数组中，并能够访问另一个活动中的数据数组。我会为此做一个Intent并将其作为额外的传递吗？我一直在搜索，但没有得到一个明确的答案。我希望能够访问该数据数组，以便我可以在另一个活动中随机显示它。

ListView.Java

    public class ListView extends AppCompatActivity {
    private static final String TAG = "ListView";

    private EditText editText;
    private android.widget.ListView listView;

    DatabaseHelper mDatabaseHelper;
    Button btnAdd;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_view);
        mDatabaseHelper = new DatabaseHelper(this);
        btnAdd = (Button) findViewById(R.id.btnAdd);
        editText = (EditText) findViewById(R.id.editText);
        listView = (android.widget.ListView) findViewById(R.id.lv);


        ArrayList<String> list = getIntent().getStringArrayListExtra("myList");

        android.widget.ListView lv = (android.widget.ListView) findViewById(R.id.lv);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);

        lv.setAdapter(adapter);


        //Takes user back to the main activity after clicking on back arrow
        ImageView ivBack = (ImageView) findViewById(R.id.ivBackArrow);
        ivBack.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG, "onClick: pressed back arrow");
                Intent intent = new Intent(ListView.this, MainActivity.class);
                startActivity(intent);
            }
        });

        //Adds new hashtag to list and prompts if nothing is entered
        btnAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String newEntry = editText.getText().toString();

                if (editText.length() != 0) {
                    addData(newEntry);
                    editText.setText("");
                } else {
                    toastMessage("you must put something in the text field");
                }
            }
        });

        populateListView();
    }

    /**
     * Adds new data into the Database
     * @param newEntry
     */
    public void addData(String newEntry) {
        boolean insertData = mDatabaseHelper.addData(newEntry);

        if (insertData) {
            toastMessage("Successfully inserted");
            recreate();
        } else {
            toastMessage("Whoops, something went wrong");
        }
    }

    /**
     * Default toastMessage
     * @param message
     */
    private void toastMessage(String message) {
        Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
    }

    /**
     * Populate listView with data and create listener to navigate to editDeleteList
     */
    private void populateListView() {
        Log.d(TAG, "populateListView: displaying data in the listview");

        //get data and append to list
        Cursor data = mDatabaseHelper.getData();
        ArrayList<String> listData = new ArrayList<>();
        while(data.moveToNext()) {
            //get the value from the database in column 1
            //set it to the arraylist
            listData.add(data.getString(1));
        }
        //create arraylist and set it to the adapter
        ListAdapter adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listData);
        listView.setAdapter(adapter);

        //set onclick listen to edit activity
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
                String name = adapterView.getItemAtPosition(position).toString();
                Log.d(TAG, "onItemClick: you clicked on " + name);

                Cursor data = mDatabaseHelper.getItemID(name); //get the id associated with that name
                int itemID = -1;
                while (data.moveToNext()) {
                    itemID = data.getInt(0);
                }
                if (itemID > -1) {
                    Log.d(TAG, "onItemID: the ID is: " + itemID);
                    Intent editScreenIntent = new Intent(ListView.this, EditDeleteList.class);
                    editScreenIntent.putExtra("id",itemID);
                    editScreenIntent.putExtra("name",name);
                    startActivity(editScreenIntent);
                } else {
                    toastMessage("No ID found");
                }
            }
        });
    }

    /**
     * Updates the listView after navigating back from EditDeleteList activity
     */
    @Override
    protected void onResume() {
        super.onResume();
        populateListView();
    }
}

Answer 1

1. 从listView获取数据：

   public static String[] getStringArray(ListAdapter adapter){
   String[] a = new String[adapter.getCount()];
   for (int i = 0; i < a.length; i++)
   a[i] = adapter.getItem(i).toString();
   return a;}  

   String[] array = getStringArray(myListView.getAdapter());
2. 将数组从活动发送到另一个：

   Intent intent = new Intent(context, Class.class);
   intent.putExtra("mylist", array);

3. 在另一项活动中获取它： ArrayList<String> myList = (ArrayList<String>) getIntent().getSerializableExtra("mylist");
4. 如果ArrayList<E>类型是Serializable，您可以以相同的方式传递E。

Answer 2

我假设1）您正在修改ListView，2）按下按钮，您想要转到另一个活动，并从Activity2中的listview更新数据。从ListView的适配器，您可以创建一个将由Activity1实现的接口（UpdateListListener）。每当你按下按钮（编辑后）你只需a）调用notifyDatasetChanged（）并在实现的方法监听器（onUpdatedList（））上，您只需将列表发送到具有intent的其他活动。由于List是一个对象，您需要发送如下意图：

Intent intent = new Intent(this,Activity2.class);
intent.putExtra("myList", ListOfItems);
startActivity(intent);

ListOfItems实现Parcelable的位置。您需要研究Parcelable的工作原理。