Question

我正在创建一个简单的程序，它将文本和计数存储在表中。此数据显示在listView中。我无法获取数据以及何时更新。但是，当我关闭并打开应用程序时，数据加载正常。我已经加入了我的计划。

MainActivity：

dailyAt()

数据库处理器：

public class MainActivity extends AppCompatActivity {

    private List<Habit> habits;
    private ListAdapter adapter;
    private DatabaseHandler handler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = ( Toolbar ) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        handler = new DatabaseHandler(getApplicationContext());
        habits = handler.getAllHabit();
        View empty = getLayoutInflater().inflate(R.layout.list_item_empty, null, false);
        addContentView(empty, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
        ListView habitList = ( ListView ) findViewById(R.id.habitList);
        adapter = new ListAdapter(habits);
        if ( habitList != null ) {
            habitList.setAdapter(adapter);
            habitList.setEmptyView(empty);
            habitList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    Habit habit = ( Habit ) adapter.getItem(position);
                    habit.updateCount();
                    handler.updateHabit(habit);
                    updateList();
                }
            });
            habitList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
                @Override
                public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
                    Habit habit = (Habit) adapter.getItem(position);
                    handler.deleteHabit(habit);
                    updateList();
                    return true;
                }
            });
        }
    }


    private void getNewHabit() {

        final AlertDialog.Builder alertDialog = new AlertDialog.Builder(new ContextThemeWrapper(this, R.style.Dialog));
        alertDialog.setTitle("New Habit");
        alertDialog.setMessage("Enter the name of the new habit");
        final EditText input = new EditText(getApplicationContext());
        int padding = Math.round(getResources().getDimension(R.dimen.margin));
        input.setPadding(padding,padding,padding,padding);
        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
        input.setLayoutParams(params);
        alertDialog.setView(input);
        alertDialog.setPositiveButton("Add", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Habit habit = new Habit();
                habit.setHabit(input.getText().toString());
                habit.setCount(0);
                handler.addHabit(habit);
                updateList();
            }
        });
        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });
        alertDialog.show();
    }

    private void updateList() {
        habits.clear();
        habits = handler.getAllHabit();
        adapter.notifyDataSetChanged();
    }
}

Answer 1

我得到了它的工作。我不知道这是否是正确的方法，或者它是否只是一种解决方法。在updateList()方法中，我更改了行

habits = handler.getAllHabit();

到

habits.addAll(handler.getAllHabit());

使用AlertDialog添加项目后，listView立即立即更新。

Answer 2

只要数据库中有更新，就使用SimpleCursorAdapter并在适配器对象上调用changeCursor(newCursor)。

将cursorAdpater声明为实例变量：

SimpleCursorAdapter cursorAdapter;

然后在onCreate中，初始化cursorAdapter并在listview上设置它：

Cursor cursor = handler.getAllHabit();//Change the return type of your getAllHabit method to Cursor
String[] from = new String[]{"name","count"};//database column names
int[] to = new int[]{R.id.tvName,R.id.tvCount};//TextView id's from custom list row layout
cursorAdapter = new SimpleCursorAdapter(this,R.layout.list_row,cursor,from,to,CursorAdapter.FLAG_AUTO_REQUERY);
habitList.setAdapter(cursorAdapter);

每当数据库中有任何更新时，将更新的数据放入新游标并在cursorAdapter上调用changeCursor()并传递新游标。

Cursor newCursor = handler.getAllHabit();
cursorAdapter.changeCursor(newCursor);

Answer 3

使用finishAffinity()这种方法完成此活动，并尝试完成其下方的所有活动在具有相同亲和力的当前任务中。

ActivityCompat.finishAffinity(this);

无法从数据库中获取数据

3 个答案: