我花了很多时间搜索和阅读类似的帖子，但似乎没有一个真正反映我的问题，因此我没有找到任何适合我的东西。 我有一个数据库，我在其上执行查询，其结果存储在游标中。这有两件事： - 每次按下某个按钮时执行查询（因此查询位于该Button的OnClickListener内） - 查询返回带有String值的两个不同列，必须单独处理（一列存储必须在ListView中显示的名称，另一列存储与行关联的图像的路径） 我的问题是，我尝试创建一个String []，我需要将其传递给ListView的ArrayAdapter创建者，但尝试为其指定大小为Cursor的getCount（）会导致我的活动崩溃。我希望代码更多的是解释：
OnClickListener searchListener = new OnClickListener() {
public void onClick(View v) {
CardDatabaseOpenHelper helper = new
CardDatabaseOpenHelper(DeckEditorScreen1.this);
SQLiteDatabase db = helper.getReadableDatabase();
String columns[] = {"name","number","path"};
Cursor c = db.query("cards", columns, null, null, null, null, "number");
int count = c.getCount();
String[] resultNameStrings;
if (count != 0) resultNameStrings = new String[count];
else {resultNameStrings = new String[1]; resultNameStrings[1] = "No results";}
// This is the offending code
//Note that if I assign fixed values to resutNameStrings, the code works just
//fine
for (int i = 0; i < count; ++i) {
c.moveToNext();
int col = c.getColumnIndex("name");
String s = c.getString(col);
//Ideally here I would to something like:
//resultNameStrings[i] = s;
col = c.getColumnIndex("number");
int conv = c.getInt(col);
col = c.getColumnIndex("path");
String s2 = c.getString(col);
}
db.close();
ArrayAdapter<?> searchResultItemAdapter = new ArrayAdapter<String>
(DBScreen.this,
R.layout.search_result_item,
resultNameStrings);
ListView searchResultList = (ListView)
DBScreen.this.findViewById(R.id.search_result_list);
searchResultList.setAdapter(searchResultItemAdapter);
}
};
Button search_button = (Button) findViewById(R.id.search_button);
search_button.setOnClickListener(searchListener);
答案 0 :(得分：1)
已编辑 两次：）
在“Android Way”中执行...
首先使用CursorAdapter（fx：具有覆盖的SimpleCursorAdapter
public Cursor runQueryOnBackgroundThread(CharSequence constraint) {
Cursor cursor = managedQuery(MobileTraderProvider.CONTENT_URI,
null, null, new String[] { constraint.toString() }, null);
return cursor;
}
然后
customAdapter.getFilter().filter(filterText)
// it will call runQueryOnBackgroundThread
第二次使用ContentProvider（它将为您管理curosors ......如果数据发生变化，它甚至会重新查询）
编辑：
首先真正使用我的建议
之前的第二个
for (int i = 0; i < count; ++i) {
c.moveToNext();
//...
添加c.moveToFirst（）;
thrid：使用
if(c.moveToNext())
{
int col = c.getColumnIndex("name");
//..... rest goes here
}
第二次编辑：
MyProvider.java
public class MyProvider extends ContentProvider {
static final String LTAG = "MyAppName";
public static final Uri CONTENT_URI = Uri.parse("content://my.app.Content");
static final int CARDS = 1;
static final int CARD = 2;
public static final String CARDS_MIME_TYPE = ContentResolver.CURSOR_DIR_BASE_TYPE + "/Cards";
public static final String CARD_MIME_TYPE = ContentResolver.CURSOR_ITEM_BASE_TYPE + "/Cards";
static final UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
static final HashMap<String, String> map = new HashMap<String, String>();
static {
//static "Constructor"
matcher.addURI(Constants.AUTHORITY, "Cards", LISTS);
matcher.addURI(Constants.AUTHORITY, "Cards/*", LIST);
map.put(BaseColumns._ID, "ROWID AS _id");
map.put(Tables.Cards.C_NAME, Tables.Cards.C_NAME);
map.put(Tables.Cards.C_NUMBER, Tables.Cards.C_NUMBER);
map.put(Tables.Cards.C_PATH, Tables.Cards.C_PATH);
}
private CardDatabaseOpenHelper mDB;
@Override
public boolean onCreate() {
try {
mDB = new CardDatabaseOpenHelper(getContext());
} catch (Exception e) {
Log.e(LTAG, e.getLocalizedMessage());
}
return true;
}
public int delete(Uri uri, String selection, String[] selectionArgs) {
String table = null;
switch (matcher.match(uri)) {
case CARD:
//overriding selection and selectionArgs
selection = "ROWID=?";
selectionArgs = new String[] { uri.getPathSegments().get(1) };
table = uri.getPathSegments().get(0);
break;
case CARDS:
//this version will delete all rows if you dont provide selection and selectionargs
table = uri.getPathSegments().get(0);
break;
default:
throw new IllegalArgumentException("Unknown URL " + uri);
}
int ret = mDB.getWritableDatabase().delete(table, selection, selectionArgs);
getContext().getContentResolver().notifyChange(Uri.withAppendedPath(CONTENT_URI, table), null);
return ret;
}
@Override
public String getType(Uri uri) {
switch (matcher.match(uri)) {
case CARDS:
return CARDS_MIME_TYPE;
case CARD:
return CARD_MIME_TYPE;
default:
throw new IllegalArgumentException("Unknown URL " + uri);
}
}
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
String table, rowid;
switch (matcher.match(uri)) {
case CARD:
//overriding selection and selectionArgs
selection = "ROWID=?";
selectionArgs = new String[] { uri.getPathSegments().get(1) };
table = uri.getPathSegments().get(0);
break;
case CARDS:
//this version will update all rows if you dont provide selection and selectionargs
table = uri.getPathSegments().get(0);
break;
default:
throw new IllegalArgumentException("Unknown URL " + uri);
}
int ret = mDB.getWritableDatabase().update(table, values, selection, selectionArgs);
getContext().getContentResolver().notifyChange(Uri.withAppendedPath(CONTENT_URI, table), null);
return ret;
}
public Uri insert(Uri uri, ContentValues values) {
String table = null;
switch (matcher.match(uri)) {
case CARDS:
table = uri.getPathSegments().get(0);
break;
default:
throw new IllegalArgumentException("Unknown URL " + uri);
}
mDB.getWritableDatabase().insert(table, null, values);
getContext().getContentResolver().notifyChange(Uri.withAppendedPath(CONTENT_URI, table), null);
return null;
}
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder builder = new SQLiteQueryBuilder();
switch (matcher.match(uri)) {
case CARDS:
builder.setTables(uri.getPathSegments().get(0));
break;
case CARD:
builder.setTables(uri.getPathSegments().get(0));
selection = "ROWID=?";
selectionArgs = new String[] { uri.getPathSegments().get(1) };
default:
throw new IllegalArgumentException("Unknown URL " + uri);
}
builder.setProjectionMap(map);
Cursor cursor = builder.query(mDB.getReadableDatabase(), projection, selection, selectionArgs, null, null, sortOrder);
if (cursor == null) {
return null;
}
cursor.setNotificationUri(getContext().getContentResolver(), uri);
return cursor;
}
}
CardCursorAdapter.java
class CardCursorAdapter extends SimpleCursorAdapter {
public MyCursorAdapter(Context context, int layout, Cursor c,
String[] from, int[] to) {
super(context, layout, c, from, to);
}
@Override
public Cursor runQueryOnBackgroundThread(CharSequence constraint) {
//search in cards.name
String selection = Tables.Cards.C_NAME + " LIKE ?";
String[] selectionArgs = new String[] {"%" + constraint.toString() + "%"};
Cursor cursor = managedQuery(Uri.withAppendedPath(MyProvider.CONTENT_URI, Tables.Cards.Name),
getCursor().getColumnNames(), selection, selectionArgs, null);
return cursor;
}
}
Tables.java
public static class Tables {
//table definition
public static interface Cards {
public static final String NAME = "cards";
public static final String C_NAME = "name";
public static final String C_NUMBER = "number";
public static final String C_PATH = "path";
}
//other tables go here
}
的AndroidManifest.xml
</manifest>
</application>
<!-- ....... other stuff ....... -->
<provider android:name="MyProvider" android:authorities="my.app.Content" />
</application>
</manifest>
然后在活动中
onCreate(...){
listView.setAdapter(new CardCursorAdapter(this, R.layout.listrow,
managedQuery(Uri.withAppendedPath(MyProvider.CONTENT_URI, Tables.Cards.NAME),
new String[] { BaseColumns._ID, Tables.Cards.C_NAME, Tables.Cards.C_NUMBER, Tables.Cards.C_PATH },
null,null, number),
new String[] { Tables.Cards.C_NAME, Tables.Cards.C_NUMBER, Tables.Cards.C_PATH },
new int[] { R.id.tName, R.id.tNumber, R.id.tPath }));
}
OnClickListener searchListener = new OnClickListener() {
public void onClick(View v) {
DeckEditorScreen1.this.listView.getAdapter().getFilter().filter("text for search in name column of card table set me to empty for all rows");
}
}
答案 1 :(得分：0)
好的，我做了一些测试，我想我知道是什么问题。 Java允许构造如：
String[] whatever;
if (something) whatever = new String[avalue];
else whatever = new String[anothervalue];
如果您没有为[i]的每个字段分配具体值，则会发生崩溃。剩下的代码现在很好，虽然我添加了Selvin的修正
if (c.moveToNext) ...
c.moveToFirst（）在我的情况下未正确使用，因为for迭代计数次数。如果先执行moveToFirst，则总是缺少光标指向的第一个元素。