Question

我有一个包含listview的活动，活动（MainActivity）启动另一个活动（HomeworkAddActivity），这将从用户检索一个字符串并将其添加到listview（以上所有内容）作品）。

然而，为了让listview在其他活动启动时'记住'其内容，我尝试将列表保存到文件中，代码：

public void saveHomework() {
    try {
        @SuppressWarnings("resource")
        FileOutputStream fos = new FileOutputStream(homeworkFileName);
        fos = openFileOutput(homeworkFileName,
                Context.MODE_PRIVATE);
        ObjectOutputStream os = new ObjectOutputStream(fos);
        os.writeObject(homeworkItems);
        os.close();
        fos.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

@SuppressWarnings("unchecked")
public void populateHomework() {
    try {
        @SuppressWarnings("resource")
        FileInputStream fis = new FileInputStream(homeworkFileName);
        fis = getParent().openFileInput(homeworkFileName);
        ObjectInputStream is = new ObjectInputStream(fis);
        homeworkItems = (ArrayList<String>) is.readObject();
        is.close();
        fis.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (StreamCorruptedException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
}

然后我从文件中读到它。

saveHomework被称为onPause

和populateHomework：

    @Override
public void onResume() {
    super.onResume();
    homeworkItems = new ArrayList<String>();
    activity = this;
    homeworkListAdapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, homeworkItems);
    populateHomework();
    homeworkListAdapter.notifyDataSetChanged();
}

然而，它只显示addHomeworkActivity添加的项目，而不是“已保存”和“已恢复”的项目（它们未成功保存/恢复），为什么会这样？

Answer 1

它有2个问题

您的列表视图仍与旧适配器连接
notifyDataSetChanged在您的情况下可能不起作用，它与此答案有关

notifyDataSetChanged example

您需要在onResume（）

@Override
public void onResume() {
    super.onResume();
    homeworkItems = new ArrayList<String>();
    activity = this;
    populateHomework(); // I move this line up
    homeworkListAdapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, homeworkItems);

    //homeworkListAdapter.notifyDataSetChanged(); // this line might not work
    yourListView.setAdapter(homeworkListAdapter); // because your listview still connect with your old ArrayAdapter

}

我的arrayList没有成功保存和恢复？

1 个答案: