Question

在我的活动中，我有ActionBar，其中包含一个新的动作按钮（在ListView上添加一个新项目）和一个ListView。问题是，在我添加一些项目然后按下后退按钮后，ListView将返回上一个ListView并减少项目，并在一两秒后显示包含所有项目的完整列表视图。我认为这个问题类似于listview与之前的重复。这是我的活动：

public class ListNotesActivity extends ActionBarActivity {

private ArrayList<Note> notes;
private Database db;
private long lastBackPressTime = 0;
private Toast toast;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_notes);
    notes = new ArrayList<Note>();
    db = new Database(this);
    getNotes();
    ActionBar ab = getSupportActionBar();
    ab.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#E89619")));
    ab.setTitle("Your notes");
}

@Override
public void onBackPressed() {
    if (this.lastBackPressTime < System.currentTimeMillis() - 4000) {
        toast = Toast.makeText(this, "Press back again to exit", 4000);
        toast.show();
        this.lastBackPressTime = System.currentTimeMillis();
    } else {
        if (toast != null) 
            toast.cancel();
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.list_notes, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    switch (id) {
    case R.id.action_new:
        //In this activity that I start, It will save the new Item in the database and then it starts this activity again that will read the database with the new item.
        Intent i = new Intent(ListNotesActivity.this,
                NotesActivity.class);
        i.putExtra(NEWNOTE, true);
        startActivity(i);
        return true;
    default:
        return super.onOptionsItemSelected(item);
    }
}

public void getNotes() {
    final Toast t = Toast.makeText(this, R.string.retrieving_notes,
            Toast.LENGTH_SHORT);
    AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {
        @Override
        protected Void doInBackground(Void... params) {
            notes = db.getNotes();
            Log.v("MyActivity",
                    "Read notes on the database: " + notes.size());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            populateList();
        }
    };
    t.show();
    task.execute();
}

public void populateList() {
    NoteAdapter adapter = new NoteAdapter(this, notes);
    final ListView listView = (ListView) findViewById(R.id.list_notes);
    listView.setAdapter(adapter);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parentView, View childView,
                int position, long id) {
            Note note = notes.get(position);
            Log.v("MyActivity",
                    "LISTNOTESACTIVITY: note's title: " + note.getTitle());
            Bundle b = new Bundle();
            b.putSerializable(EDITNOTE2, note);
            Intent i = new Intent(ListNotesActivity.this,
                    NotesActivity.class);
            i.putExtra(EDITNOTE, true);
            i.putExtra(EDITNOTE2, b);
            startActivity(i);
        }
    });
}

我希望我能说清楚。提前谢谢！

Answer 1

尝试从getNotes（）方法中删除此行

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

Answer 2

您的列表视图仅在创建活动时更新（而不是在恢复活动时），因为您只在onCreate（）中调用getNotes（）。在方法getNotes（）中，您进行异步操作。

如果您想立即更新列表视图，请采取这样的策略。

为结果启动新活动，在创建新项目之后在第二个活动中将数据传递回第一个活动。

在创建新项目后的NotesActivity中添加并调用此方法

private void saveItem(Note note)
{
     Intent data = new Intent();
     // set all data from your item
     data.putExtra(name, value);
     setResult(RESULT_OK, data);
}

在ListNotesActivity中，您应该使用此调用启动新活动

startActivityForResult(intent, 1);

并覆盖此方法

@Override
protected void onResume()
{
    super.onResume();
    // This call on your list view to update rows
    listViewAdapter.notifyDataSetChanged();
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
    if(resultCode == RESULT_OK && requestCode == 1)
    {
        Note note = new Note();
        // Extract your data from intent 
        data.getExtra(name); // and set to note variable

        // add your new item to list view adapter
        listViewAdapter.addNewItem(note);
    }
}

我希望这会对你有所帮助。

Android Listview复制按下后退按钮

2 个答案: