返回活动时不显示保存的数据

Question

当我进入应用程序更深处的不同活动并按向上按钮返回原始活动时，不会显示使用 sqlite 存储的应用程序中保存的数据。

这是由 listactivity 膨胀的 listfragment。

请注意，我将查询放在 onCreate 中，以便在返回活动时再次执行它。

package com.example.sample;

import java.util.ArrayList;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import com.actionbarsherlock.app.SherlockListFragment;

/**
 * A list fragment representing a list of Courses. This fragment also supports
 * tablet devices by allowing list items to be given an 'activated' state upon
 * selection. This helps indicate which item is currently being viewed in a
 * {@link CourseDetailFragment}.
 * <p>
 * Activities containing this fragment MUST implement the {@link Callbacks}
 * interface.
 */
public class CourseListFragment extends SherlockListFragment {

SQLiteDatabase db;
DbHelper dbHelper;
boolean bool = false;

private static String courseName;
ArrayList<String> courseItems;
ArrayAdapter<String> adapter;
/**
 * The serialization (saved instance state) Bundle key representing the
 * activated item position. Only used on tablets.
 */
private static final String STATE_ACTIVATED_POSITION = "activated_position";

/**
 * The fragment's current callback object, which is notified of list item
 * clicks.
 */
private Callbacks mCallbacks = sDummyCallbacks;

/**
 * The current activated item position. Only used on tablets.
 */
private int mActivatedPosition = ListView.INVALID_POSITION;

/**
 * A callback interface that all activities containing this fragment must
 * implement. This mechanism allows activities to be notified of item
 * selections.
 */
public interface Callbacks {
    /**
     * Callback for when an item has been selected.
     */
    public void onItemSelected(String id);
}

/**
 * A dummy implementation of the {@link Callbacks} interface that does
 * nothing. Used only when this fragment is not attached to an activity.
 */
private static Callbacks sDummyCallbacks = new Callbacks() {
    @Override
    public void onItemSelected(String id) {
    }
};

/**
 * Mandatory empty constructor for the fragment manager to instantiate the
 * fragment (e.g. upon screen orientation changes).
 */
public CourseListFragment() {
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dbHelper = new DbHelper(getActivity());
    db = dbHelper.getReadableDatabase();
    courseItems = new ArrayList<String>();
    int layout = (Build.VERSION.SDK_INT >= 11) ? android.R.layout.simple_list_item_activated_1
            : android.R.layout.simple_list_item_1;
    adapter = new ArrayAdapter<String>(getActivity(), layout, courseItems);
    // TODO: replace with a real list adapter.
    setListAdapter(adapter);

    if (bool) {
        String[] projection = { DbHelper.COURSE_NAME };
        Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null,
                null, null, null);
        c.moveToFirst();

        while (c.moveToNext()) {
            courseName = c
                    .getString(c.getColumnIndex(DbHelper.COURSE_NAME));
            courseItems.add(courseName);
        }
        c.close();
        adapter.notifyDataSetChanged();
    }
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    // Restore the previously serialized activated item position.
    if (savedInstanceState != null
            && savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
        setActivatedPosition(savedInstanceState
                .getInt(STATE_ACTIVATED_POSITION));
    }
}

public void addCourse() {
    String[] projection = { DbHelper.COURSE_NAME };
    Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null, null,
            null, null);
    c.moveToFirst();

    while (c.moveToNext()) {
        courseName = c.getString(c.getColumnIndex(DbHelper.COURSE_NAME));
        courseItems.add(courseName);
    }
    c.close();
    adapter.notifyDataSetChanged();
    bool = true;
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    // Activities containing this fragment must implement its callbacks.
    if (!(activity instanceof Callbacks)) {
        throw new IllegalStateException(
                "Activity must implement fragment's callbacks.");
    }

    mCallbacks = (Callbacks) activity;
}

@Override
public void onDetach() {
    super.onDetach();

    // Reset the active callbacks interface to the dummy implementation.
    mCallbacks = sDummyCallbacks;
}

@Override
public void onListItemClick(ListView listView, View view, int position,
        long id) {
    super.onListItemClick(listView, view, position, id);
    // Notify the active callbacks interface (the activity, if the
    // fragment is attached to one) that an item has been selected.
    mCallbacks.onItemSelected(null);

}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    if (mActivatedPosition != ListView.INVALID_POSITION) {
        // Serialize and persist the activated item position.
        outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
    }
}

/**
 * Turns on activate-on-click mode. When this mode is on, list items will be
 * given the 'activated' state when touched.
 */
public void setActivateOnItemClick(boolean activateOnItemClick) {
    // When setting CHOICE_MODE_SINGLE, ListView will automatically
    // give items the 'activated' state when touched.
    getListView().setChoiceMode(
            activateOnItemClick ? ListView.CHOICE_MODE_SINGLE
                    : ListView.CHOICE_MODE_NONE);
}

public void setActivatedPosition(int position) {
    if (position == ListView.INVALID_POSITION) {
        getListView().setItemChecked(mActivatedPosition, false);
    } else {
        getListView().setItemChecked(position, true);
    }

    mActivatedPosition = position;
}
}

为 onoviewstaterestored 更新编辑

package com.example.sample;

import java.util.ArrayList;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import com.actionbarsherlock.app.SherlockListFragment;

/**
 * A list fragment representing a list of Courses. This fragment also supports
 * tablet devices by allowing list items to be given an 'activated' state upon
 * selection. This helps indicate which item is currently being viewed in a
 * {@link CourseDetailFragment}.
 * <p>
 * Activities containing this fragment MUST implement the {@link Callbacks}
 * interface.
 */
public class CourseListFragment extends SherlockListFragment {

SQLiteDatabase db;
DbHelper dbHelper;
boolean bool = false;

private static String courseName;
ArrayList<String> courseItems;
ArrayAdapter<String> adapter;
/**
 * The serialization (saved instance state) Bundle key representing the
 * activated item position. Only used on tablets.
 */
private static final String STATE_ACTIVATED_POSITION = "activated_position";

/**
 * The fragment's current callback object, which is notified of list item
 * clicks.
 */
private Callbacks mCallbacks = sDummyCallbacks;

/**
 * The current activated item position. Only used on tablets.
 */
private int mActivatedPosition = ListView.INVALID_POSITION;

/**
 * A callback interface that all activities containing this fragment must
 * implement. This mechanism allows activities to be notified of item
 * selections.
 */
public interface Callbacks {
    /**
     * Callback for when an item has been selected.
     */
    public void onItemSelected(String id);
}

/**
 * A dummy implementation of the {@link Callbacks} interface that does
 * nothing. Used only when this fragment is not attached to an activity.
 */
private static Callbacks sDummyCallbacks = new Callbacks() {
    @Override
    public void onItemSelected(String id) {
    }
};

/**
 * Mandatory empty constructor for the fragment manager to instantiate the
 * fragment (e.g. upon screen orientation changes).
 */
public CourseListFragment() {
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dbHelper = new DbHelper(getActivity());
    db = dbHelper.getReadableDatabase();
    courseItems = new ArrayList<String>();
    int layout = (Build.VERSION.SDK_INT >= 11) ? android.R.layout.simple_list_item_activated_1
            : android.R.layout.simple_list_item_1;
    adapter = new ArrayAdapter<String>(getActivity(), layout, courseItems);
    // TODO: replace with a real list adapter.
    setListAdapter(adapter);
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    // Restore the previously serialized activated item position.
    if (savedInstanceState != null
            && savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
        setActivatedPosition(savedInstanceState
                .getInt(STATE_ACTIVATED_POSITION));
    }
}

@Override
public void onViewStateRestored(Bundle savedInstanceState) {
    super.onViewStateRestored(savedInstanceState);
    String[] projection = { DbHelper.COURSE_NAME };
    Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null, null,
            null, null);
    c.moveToFirst();

    while (c.moveToNext()) {
        courseName = c.getString(c.getColumnIndex(DbHelper.COURSE_NAME));
        courseItems.add(courseName);
    }
    c.close();
    adapter.notifyDataSetChanged();
}


@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    // Activities containing this fragment must implement its callbacks.
    if (!(activity instanceof Callbacks)) {
        throw new IllegalStateException(
                "Activity must implement fragment's callbacks.");
    }

    mCallbacks = (Callbacks) activity;
}

@Override
public void onDetach() {
    super.onDetach();

    // Reset the active callbacks interface to the dummy implementation.
    mCallbacks = sDummyCallbacks;
}

@Override
public void onListItemClick(ListView listView, View view, int position,
        long id) {
    super.onListItemClick(listView, view, position, id);
    // Notify the active callbacks interface (the activity, if the
    // fragment is attached to one) that an item has been selected.
    mCallbacks.onItemSelected(null);

}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    if (mActivatedPosition != ListView.INVALID_POSITION) {
        // Serialize and persist the activated item position.
        outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
    }
}

/**
 * Turns on activate-on-click mode. When this mode is on, list items will be
 * given the 'activated' state when touched.
 */
public void setActivateOnItemClick(boolean activateOnItemClick) {
    // When setting CHOICE_MODE_SINGLE, ListView will automatically
    // give items the 'activated' state when touched.
    getListView().setChoiceMode(
            activateOnItemClick ? ListView.CHOICE_MODE_SINGLE
                    : ListView.CHOICE_MODE_NONE);
}

public void setActivatedPosition(int position) {
    if (position == ListView.INVALID_POSITION) {
        getListView().setItemChecked(mActivatedPosition, false);
    } else {
        getListView().setItemChecked(position, true);
    }

    mActivatedPosition = position;
}
}

Answer 1

我修好了！我必须使用最初使用的 addCourse 方法更新列表视图，然后在每次活动恢复时使用 onViewStateRestored 方法更新它。就方法内部的内容而言，它们都包含相同的内容。

这是我的工作列表片段的代码。

package com.example.sample;

import java.util.ArrayList;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import com.actionbarsherlock.app.SherlockListFragment;

/**
 * A list fragment representing a list of Courses. This fragment also supports
 * tablet devices by allowing list items to be given an 'activated' state upon
 * selection. This helps indicate which item is currently being viewed in a
 * {@link CourseDetailFragment}.
 * <p>
 * Activities containing this fragment MUST implement the {@link Callbacks}
 * interface.
 */
public class CourseListFragment extends SherlockListFragment {

SQLiteDatabase db;
DbHelper dbHelper;
boolean bool = false;

private static String courseName;
ArrayList<String> courseItems;
ArrayAdapter<String> adapter;
/**
 * The serialization (saved instance state) Bundle key representing the
 * activated item position. Only used on tablets.
 */
private static final String STATE_ACTIVATED_POSITION = "activated_position";

/**
 * The fragment's current callback object, which is notified of list item
 * clicks.
 */
private Callbacks mCallbacks = sDummyCallbacks;

/**
 * The current activated item position. Only used on tablets.
 */
private int mActivatedPosition = ListView.INVALID_POSITION;

/**
 * A callback interface that all activities containing this fragment must
 * implement. This mechanism allows activities to be notified of item
 * selections.
 */
public interface Callbacks {
    /**
     * Callback for when an item has been selected.
     */
    public void onItemSelected(String id);
}

/**
 * A dummy implementation of the {@link Callbacks} interface that does
 * nothing. Used only when this fragment is not attached to an activity.
 */
private static Callbacks sDummyCallbacks = new Callbacks() {
    @Override
    public void onItemSelected(String id) {
    }
};

/**
 * Mandatory empty constructor for the fragment manager to instantiate the
 * fragment (e.g. upon screen orientation changes).
 */
public CourseListFragment() {
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dbHelper = new DbHelper(getActivity());
    db = dbHelper.getReadableDatabase();
    courseItems = new ArrayList<String>();
    int layout = (Build.VERSION.SDK_INT >= 11) ? android.R.layout.simple_list_item_activated_1
            : android.R.layout.simple_list_item_1;
    adapter = new ArrayAdapter<String>(getActivity(), layout, courseItems);
    // TODO: replace with a real list adapter.
    setListAdapter(adapter);
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    // Restore the previously serialized activated item position.
    if (savedInstanceState != null
            && savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
        setActivatedPosition(savedInstanceState
                .getInt(STATE_ACTIVATED_POSITION));
    }
}

@Override
public void onViewStateRestored(Bundle savedInstanceState) {
    super.onViewStateRestored(savedInstanceState);
    String[] projection = { DbHelper.COURSE_NAME };
    Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null, null,
            null, null);
    c.moveToFirst();

    while (c.moveToNext()) {
        courseName = c.getString(c.getColumnIndex(DbHelper.COURSE_NAME));
        courseItems.add(courseName);
    }
    c.close();
    adapter.notifyDataSetChanged();
}

public void addCourse() {
    String[] projection = { DbHelper.COURSE_NAME };
    Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null, null,
            null, null);
    c.moveToFirst();

    while (c.moveToNext()) {
        courseName = c.getString(c.getColumnIndex(DbHelper.COURSE_NAME));
        courseItems.add(courseName);
    }
    c.close();
    adapter.notifyDataSetChanged();
    bool = true;
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    // Activities containing this fragment must implement its callbacks.
    if (!(activity instanceof Callbacks)) {
        throw new IllegalStateException(
                "Activity must implement fragment's callbacks.");
    }

    mCallbacks = (Callbacks) activity;
}

@Override
public void onDetach() {
    super.onDetach();

    // Reset the active callbacks interface to the dummy implementation.
    mCallbacks = sDummyCallbacks;
}

@Override
public void onListItemClick(ListView listView, View view, int position,
        long id) {
    super.onListItemClick(listView, view, position, id);
    // Notify the active callbacks interface (the activity, if the
    // fragment is attached to one) that an item has been selected.
    mCallbacks.onItemSelected(null);

}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    if (mActivatedPosition != ListView.INVALID_POSITION) {
        // Serialize and persist the activated item position.
        outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
    }
}

/**
 * Turns on activate-on-click mode. When this mode is on, list items will be
 * given the 'activated' state when touched.
 */
public void setActivateOnItemClick(boolean activateOnItemClick) {
    // When setting CHOICE_MODE_SINGLE, ListView will automatically
    // give items the 'activated' state when touched.
    getListView().setChoiceMode(
            activateOnItemClick ? ListView.CHOICE_MODE_SINGLE
                    : ListView.CHOICE_MODE_NONE);
}

public void setActivatedPosition(int position) {
    if (position == ListView.INVALID_POSITION) {
        getListView().setItemChecked(mActivatedPosition, false);
    } else {
        getListView().setItemChecked(position, true);
    }

    mActivatedPosition = position;
}
}