如何使用共享首选项保存列表视图

Question

我制作了一个简单的购物清单应用程序，用户可以在其中将项目添加到列表视图。 我的问题是当我离开应用程序时，项目不会保存。 我认为我需要使用共享偏好，但没有太多看实现它（我对编码相当陌生）如果有人知道如何实现共享偏好以便我的项目将保存它，将不胜感激。

我的代码：

public class CreateAList extends AppCompatActivity {
    //ArrayList for data
    private ArrayList<String> list = new ArrayList<>();
    ListView list_view;
    ArrayAdapter arrayAdapter;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_create_alist);
        //find view by id
        list_view = findViewById(R.id.list_view);
        arrayAdapter = new ArrayAdapter(CreateAList.this, android.R.layout.simple_list_item_1,list);
        list_view.setAdapter(arrayAdapter);



        list_view.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(final AdapterView<?> adapterView, View view, final int i, long l) {

                //Inflating is the process of adding a view(.xml) to activity on runtime
                PopupMenu popupMenu = new PopupMenu(CreateAList.this,view);
                popupMenu.getMenuInflater().inflate(R.menu.pop_up_menu,popupMenu.getMenu());

                popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                    @Override
                    public boolean onMenuItemClick(MenuItem menuItem) {

                            switch (menuItem.getItemId()){

                                case R.id.item_update:
                                    //function for update
                                    AlertDialog.Builder builder = new AlertDialog.Builder(CreateAList.this);
                                    View v = LayoutInflater.from(CreateAList.this).inflate(R.layout.item_dialog,null,false);
                                    builder.setTitle("Update Item");
                                    final EditText editText = v.findViewById(R.id.editItem);
                                    editText.setText(list.get(i));


                                    //set custom view to dialog
                                    builder.setView(v);

                                    builder.setPositiveButton("Update", new DialogInterface.OnClickListener(){
                                        @Override
                                        public void onClick(DialogInterface dialog, int which) {
                                            if (!editText.getText().toString().isEmpty()){
                                                list.set(i, editText.getText().toString().trim());
                                                arrayAdapter.notifyDataSetChanged();
                                                Toast.makeText(CreateAList.this, "Item Updated", Toast.LENGTH_SHORT).show();
                                            }else{
                                                editText.setError("add item here!");
                                            }
                                        }
                                    });

                                    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                                        @Override
                                        public void onClick(DialogInterface dialog, int i) {
                                            dialog.dismiss();
                                        }
                                    });

                                    builder.show();

                                    break;

                                case R.id.item_delete:
                                    //function for delete
                                    Toast.makeText(CreateAList.this, "Item Deleted", Toast.LENGTH_SHORT).show();
                                   list.remove(i);
                                   arrayAdapter.notifyDataSetChanged();

                                   break;

                            }

                        return true;
                    }
                });
                    popupMenu.show();
            }
        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu,menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()){
            case R.id.add_item:

                //function to add

                addItem();

                break;

        }

        return true;
    }
//method for adding item
    private void addItem() {
        AlertDialog.Builder builder = new AlertDialog.Builder(CreateAList.this);
        builder.setTitle("Add new Item");

        View v = LayoutInflater.from(CreateAList.this).inflate(R.layout.item_dialog,null,false);

        builder.setView(v);
        final EditText editItem = v.findViewById(R.id.editItem);
        builder.setPositiveButton("Add", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                if (!editItem.getText().toString().isEmpty()){
                    list.add(editItem.getText().toString().trim());
                    arrayAdapter.notifyDataSetChanged();
                }else{
                    editItem.setError("Add Item Here!");
                }

            }
        });
}

Answer 1

通过共享偏好教程来 go 将是一个好主意。 这样你会学到更多。 另请查找 Android 提供的用于存储数据的 SQLite 数据库。 如果您的列表视图中有简单的对象，我认为这将是更好的方法。

这是一个很好的教程： https://medium.com/@evancheese1/shared-preferences-saving-arraylists-and-more-with-json-and-gson-java-5d899c8b0235

Answer 2

void putSharedPreferencesStringSet（字符串键，设置值）

{
    SharedPreferences.Editor edit = getContext().getSharedPreferences("SHARED_PREFERENCE_NAME", 0).edit();
    edit.putStringSet(key, value);
    edit.apply();
}

void putSharedPreferencesStringSet(String key, String value)
{
    SharedPreferences.Editoredit = getContext().getSharedPreferences("SHARED_PREFERENCE_NAME", 0).edit();
    edit.putString(key, value);
    edit.apply();
}

String getSharedPreferencesString(String key)
{
    SharedPreferences prefs = AppConstants.appContext.getSharedPreferences(AppConstants.SHARED_PREFERENCE_NAME, 0);
    return prefs.getString(key, 0);
}

void removeSharedPreferencesString(String key)
{
    SharedPreferences edit = AppConstants.appContext.getSharedPreferences(AppConstants.SHARED_PREFERENCE_NAME, 0);
    edit.remove(key);
    edit.apply();

}

//以上函数是关于添加、获取和删除sharedPrefrences

如果您在将商品添加到购物车时需要使用数据库的另一种方法