当我回按钮时,前一个Activity中的值丢失,但是当调用this.finish()时则没有

Question

所以我有一个奇怪的问题.我正在进行2项活动.其中一个活动显示一个ListView,其数据通过一个很长的Extra来获取,我用它来通过database.query中的WHERE子句获取结果.单击ListView项时会调用另一个Activity,允许某人向ListView的数据库添加内容.

活动名称是DaysActivity.java(列表视图DayAddActivity.java的活动)和(允许某人添加一天的活动,然后显示在DaysActivity.javaListView中).

我遇到的问题是,当finish() DayAddActivity.java它返回时DaysActivity,ListView仍然完全填充.但是,如果我点击后退按钮DayAddActivity.java(带有我的应用程序图标的操作栏中标题左侧的按钮),当它返回到DaysActivity.java时,ListView为空/消失.

下面是两个代码:

DaysActivity.java:

package com.gauvion.gfit;

import android.annotation.SuppressLint;
import android.app.ListActivity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.database.Cursor;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;

public class DaysActivity extends ListActivity {

    private DaysDataSource datasource;
    private SimpleCursorAdapter dataAdapter;
    private boolean isEditing = false;
    private Toast toast_deleted;
    private String[] columns = new String[] { MySQLiteHelper.COLUMN_NAME, MySQLiteHelper.COLUMN_DAY };
    private int[] to;
    private long routineDataID;
    private String routineDataName;

    @SuppressLint("ShowToast")
    @Override
    public void onCreate(Bundle savedInstanceState) {       
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_days); 

        routineDataID = getIntent().getLongExtra("routineDataID", 0);
        routineDataName = getIntent().getStringExtra("routineDataName");
        setTitle(routineDataName);

        toast_deleted = Toast.makeText(this, "", Toast.LENGTH_SHORT);
        datasource = new DaysDataSource(this);
        datasource.open();

        Cursor cursor = datasource.fetchAllDays(routineDataID);
        to = new int[] { R.id.listitem_day_name, R.id.listitem_day_day };
        dataAdapter = new SimpleCursorAdapter(this, R.layout.listitem_day, cursor, columns, to, 0);
        setListAdapter(dataAdapter);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {     
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.activity_days, menu);
        return true;        
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {     
        Cursor cursor = datasource.fetchAllDays(routineDataID);
        switch (item.getItemId()) {
        case R.id.button_days_add:
            Intent startDayAdd = new Intent(this, DayAddActivity.class);
            startDayAdd.putExtra("routineDataID", routineDataID);
            this.startActivity(startDayAdd);
            return true;

        case R.id.button_days_edit:
            to = new int[] { R.id.listitem_day_edit_name, R.id.listitem_day_edit_day };
            dataAdapter = new SimpleCursorAdapter(this, R.layout.listitem_day_edit, cursor, columns, to, 0);
            setListAdapter(dataAdapter);

            isEditing = true;
            invalidateOptionsMenu();
            return true;

        case R.id.button_days_edit_done:
            to = new int[] { R.id.listitem_day_name, R.id.listitem_day_day };
            dataAdapter = new SimpleCursorAdapter(this, R.layout.listitem_day, cursor, columns, to, 0);
            setListAdapter(dataAdapter);

            isEditing = false;
            invalidateOptionsMenu();
            return true;

        default:
            return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);

        menu.findItem(R.id.button_days_edit).setVisible(!isEditing);
        menu.findItem(R.id.button_days_edit_done).setVisible(isEditing);

        return true;
    }

    @Override
    protected void onResume() {
        datasource.open();
        Cursor cursor = datasource.fetchAllDays(routineDataID);
        dataAdapter.changeCursor(cursor);

        super.onResume();
    }

    @Override
    protected void onPause() {
        datasource.close();
        super.onPause();
    }

} 

DayAddActivity.java:

package com.gauvion.gfit;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;
import android.support.v4.app.NavUtils;

public class DayAddActivity extends Activity {
    private RoutinesDataSource datasource;
    private EditText dayName;
    private Spinner dayDay;
    private Button saveButton;
    private long routineDataID;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_day_add);
        routineDataID = getIntent().getLongExtra("routineDataID", 0);
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case android.R.id.home:
            NavUtils.navigateUpFromSameTask(this);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public void cancelDay(View view) {
        this.finish();
    }

}

cancelDay()单击"取消"按钮时会调用该函数activity_day_add.xml.就像我说的,当我点击里面的"取消"按钮时DayAddActivity.java,它会返回到DaysActivity.javaListView就可以了.所有数据都在那里.但是,如果我按下操作栏中的后退按钮(包含后面箭头的按钮和活动标题旁边的应用程序图标),ListView for DaysActivity.java为空/消失,标题也为空(因为这也是生成的)通过Extra String值).

Answer 1

您的游标不受活动管理，这可能会导致内存泄漏甚至 ANR。您应该考虑使用加载器来使用游标填充列表。您可以在这里找到一个示例：http://developer.android.com/guide/components/loaders.html。

加载器工作得更好，因为在获得与数据库的连接时它们不会冻结应用程序，并且它们将从活动的一个实例传递到另一个实例，从而防止内存泄漏和重用资源。

但同样，正如您在上一篇文章中所说：额外内容似乎在 onResume() 中丢失，您应该了解 onSaveInstanceState 和 onCreate 之间的链接，以将参数传递给活动的未来自身。看这个帖子，得分最高的答案是：onSaveInstanceState()和onRestoreInstanceState()。