我有一个新闻阅读器应用程序，如果你想稍后阅读它们，它有一个数据库来保存故事，但是我无法在savedStoriesActivity上显示这些故事。这是DB类：
public class newsReaderDB {
RSSItem insertRSSItem = new RSSItem();
// database constants
public static final String DB_NAME = "newsReader.db";
public static final int DB_VERSION = 1;
//table constants
public static final String newsReader_TABLE = "savedStories";
public static final String storyID = "_id";
public static final int storyID_COL = 0;
public static final String storyName = "storyName";
public static final int storyName_COL = 2;
public static final String storyDescription = "Description";
public static final int storyDescription_COL = 3;
public static final String storyLink = "storyLink";
public static final int storyLink_COL = 4;
public static final String storySource = "storySource";
public static final int storySource_COL = 5;
public static final String CREATE_newsReader_TABLE =
"CREATE TABLE " + newsReader_TABLE + " (" +
storyID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
storyName + " INTEGER, " +
storyDescription + " TEXT, " +
storyLink + " TEXT, " +
storySource + " TEXT);";
public static final String DROP_newReader_TABLE =
"DROP TABLE IF EXISTS " + newsReader_TABLE;
private static class DBHelper extends SQLiteOpenHelper {
public DBHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
// create tables
db.execSQL(CREATE_newsReader_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db,
int oldVersion, int newVersion) {
Log.d("Task list", "Upgrading db from version "
+ oldVersion + " to " + newVersion);
db.execSQL(newsReaderDB.DROP_newReader_TABLE);
onCreate(db);
}
}
// database and database helper objects
private SQLiteDatabase db;
private DBHelper dbHelper;
public newsReaderDB(Context context) {
dbHelper = new DBHelper(context, DB_NAME, null, DB_VERSION);
}
private void openReadableDB() {
db = dbHelper.getReadableDatabase();
}
private void openWriteableDB() {
db = dbHelper.getWritableDatabase();
}
private void closeDB() {
if (db != null)
db.close();
}
public ArrayList<RSSItem> getLists() {
ArrayList<RSSItem> lists = new ArrayList<RSSItem>();
openReadableDB();
Cursor cursor = db.query(newsReader_TABLE,
null, null, null, null, null, null);
while (cursor.moveToNext()) {
RSSItem list = new RSSItem();
list.setId(Integer.parseInt(cursor.getString(storyID_COL)));
list.setTitle(cursor.getString(storyName_COL));
list.setDescription(cursor.getString(storyDescription_COL));
list.setLink(cursor.getString(storyLink_COL));
list.setSource(cursor.getString(storySource_COL));
lists.add(list);
}
if (cursor != null)
cursor.close();
closeDB();
return lists;
}
public RSSItem getList(String name) {
String where = storyName + "= ?";
String[] whereArgs = { name };
openReadableDB();
Cursor cursor = db.query(newsReader_TABLE, null,
where, whereArgs, null, null, null);
RSSItem list = null;
cursor.moveToFirst();
list = new RSSItem();
list.setId(cursor.getInt(storyID_COL));
list.setTitle(cursor.getString(storyName_COL));
list.setDescription(cursor.getString(storyDescription_COL));
list.setLink(cursor.getString(storyLink_COL));
list.setSource(cursor.getString(storySource_COL));
if (cursor != null)
cursor.close();
this.closeDB();
return list;
}
public ArrayList<RSSItem> getStories(String storyName) {
String where =
storyID + " = ?";
int listID = getList(storyName).getId();
String[] whereArgs = { Integer.toString(listID) };
this.openReadableDB();
Cursor cursor = db.query(newsReader_TABLE, null,
where, whereArgs,
null, null, null);
ArrayList<RSSItem> tasks = new ArrayList<RSSItem>();
while (cursor.moveToNext()) {
tasks.add(getStoryFromCursor(cursor));
}
if (cursor != null)
cursor.close();
this.closeDB();
return tasks;
}
private static RSSItem getStoryFromCursor(Cursor cursor) {
if (cursor == null || cursor.getCount() == 0){
return null;
}
else {
try {
RSSItem story = new RSSItem();
story.setTitle(cursor.getString(storyName_COL));
story.setSource(cursor.getString(storySource_COL));
story.setDescription(cursor.getString(storyDescription_COL));
story.setLink(cursor.getString(storyLink_COL));
return story;
}
catch(Exception e) {
return null;
}
}
}
public long insertStory(RSSItem story) {
ContentValues cv = new ContentValues();
cv.put(storyName, story.getTitle());
cv.put(storyDescription, story.getDescription());
cv.put(storyLink, story.getLink());
cv.put(storySource, story.getSource());
this.openWriteableDB();
long rowID = db.insert(newsReader_TABLE, null, cv);
this.closeDB();
return rowID;
}
public int deleteStory(long id) {
String where = storyID+ "= ?";
String[] whereArgs = { String.valueOf(id) };
this.openWriteableDB();
int rowCount = db.delete(newsReader_TABLE, where, whereArgs);
this.closeDB();
return rowCount;
}
}
这是我的savedStoryActivity：
public class savedStoryList extends AppCompatActivity {
SharedPreferences sharedpreferences;
private static final String pref_file = "pref_file";
private RSSItem feed;
private ArrayList<RSSItem> feeds;
private FileIO io;
private ListView listViewNews;
private HashMap items;
newsReaderDB db = new newsReaderDB(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_saved_story_list);
listViewNews = (ListView) findViewById(R.id.listViewNews);
io = new FileIO(getApplicationContext());
listViewNews.setOnItemClickListener(new android.widget.AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
items = (HashMap) listViewNews.getItemAtPosition(position);
//Date parsing
Date date = new Date();
DateFormat outputFormat = new SimpleDateFormat("yyyy.MM.dd (HH:mm)");
DateFormat inputFormat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss Z");
String inputText = feed.getPubDate();
try {
date = inputFormat.parse(inputText);
} catch (Exception e) {
Log.d("Date Parser", e.getMessage());
}
String dateOutput = outputFormat.format(date);
Intent intent = new Intent(view.getContext(), ItemActivity.class);
intent.putExtra("source", items.get("source").toString());
intent.putExtra("pubdate", dateOutput);
intent.putExtra("title", feed.getTitle());
intent.putExtra("description", feed.getDescription());
intent.putExtra("link", feed.getLink());
startActivity(intent);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_spillover_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_settings:
startActivity(new Intent(getApplicationContext(), SettingsActivity.class));
return true;
case R.id.menu_about:
startActivity(new Intent(getApplicationContext(), AboutActivity.class));
return true;
case R.id.menu_savedStories:
startActivity(new Intent(getApplicationContext(),savedStoryList.class));
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void updateDisplay() {
if (feeds == null) {
Toast.makeText(getApplicationContext(), "Feed is null", Toast.LENGTH_SHORT).show();
}
ArrayList<HashMap<String, String>> data =
new ArrayList<HashMap<String, String>>();
for (int i = 0; i < feeds.size(); ++i) {
feed = feeds.get(i);
//Date parsing
Date date = new Date();
DateFormat outputFormat = new SimpleDateFormat("yyyy.MM.dd (HH:mm)");
DateFormat inputFormat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss Z");
String inputText = feed.getPubDate();
try {
date = inputFormat.parse(inputText);
} catch (Exception e) {
Log.d("Date Parser", e.getMessage());
}
String dateOutput = outputFormat.format(date);
for (RSSItem item :feeds) {
HashMap<String, String> map = new HashMap<String, String>();
map.put("source", item.getSource());
map.put("date", dateOutput); //map.put("date", item.getPubDateFormatted());
map.put("title", item.getTitle());
data.add(map);
}
}
// create the resource, from, and to variables
int resource = R.layout.news_list;
String[] from = {"source","date", "title"};
int[] to = {R.id.lblSource, R.id.lblPubDate, R.id.lblHeadline};
// create and set the adapter
SimpleAdapter adapter =
new SimpleAdapter(this, data, resource, from, to);
listViewNews.setAdapter(adapter);
Log.d("News reader", "Feed displayed");
}
}
我以为我有它工作，但不确定什么是错的，我也没有错误。
答案 0 :(得分：0)
顺便说一下，我正在修改你的班级命名是正确的 - 以大写字母开头。
您从未在活动代码中使用过数据库...
不清楚是否存在其他错误，但您应该在onCreate内初始化数据库，其中活动的上下文不为空。
public class SavedStoryListActivity extends AppCompatActivity {
private ArrayList<RSSItem> feeds;
private ListView listViewNews;
private ArrayAdapter<RSSItem> adapter;
private NewsReaderDB db; // Don't initialize yet
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_saved_story_list);
db = new NewsReaderDB(this); // Initialize db here
listViewNews = (ListView) findViewById(R.id.listViewNews);
feeds = db.getLists();
adapter = new ArrayAdapter<RSSItem>(this, android.R.simple_list_item_1, feeds);
listViewNews.setAdapter(adapter);
}
}
正如评论中所指出的那样，您必须在某个时候致电updateDisplay()，或者实际使用NewsReaderDB db.getLists()。
您可能想尝试使用CursorAdapter的变体，这意味着将数据库值显示到ListView