光标和适配器 [英] Cursor and Adapter
本文介绍了光标和适配器的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
有人可以看到我有什么错我的光标：不返回从数据库中的数据（至少画面是空白）。我觉得这是我的问题。在DDMS显示它打开和放大器;关闭分贝。我不知道是什么光标databaseCursor = NULL;'需要。日Thnx！
该活动：
私人无效displayResultList（）{
光标databaseCursor = NULL;
DomainAdapter databaseListAdapter =新DomainAdapter（这一点，
R.layout.list_item，databaseCursor，新的String [] {标签，
标题，说明}，新的INT [] {R.id.label，
R.id.listTitle，R.id.caption}）;
databaseListAdapter.notifyDataSetChanged（）;
this.setListAdapter（databaseListAdapter）;
}
私人无效openAndQueryDatabase（）{
如果（android.os.Environment.getExternalStorageState（）。等于（
android.os.Environment.MEDIA_MOUNTED））{
。extStorageDirectory = Environment.getExternalStorageDirectory（）的toString（）;
文件DBFILE =新的文件（extStorageDirectory
+/Aero-Technologies/flyDroid/dB/flyDroid.db）;
SQLiteDatabase DB = SQLiteDatabase.openOrCreateDatabase（DBFILE，NULL）;
Log.i（DB开，标签）;
尝试 {
db.rawQuery（SELECT * FROM AC_list，NULL）;
} 最后 {
如果（DB！= NULL）
Log.i（标签，DB封闭）;
db.close（）;
}
}否则，如果（android.os.Environment.getExternalStorageState（）。等于（
android.os.Environment.MEDIA_UNMOUNTED））{
Log.i（标签，SD卡不可写/安装）;
Alerts.sdCardMissing（本）;
}
}
我的适配器：
公共类DomainAdapter扩展SimpleCursorAdapter {
私人光标dataCursor;
私人LayoutInflater mInflater;
公共DomainAdapter（上下文的背景下，INT布局，光标dataCursor，字符串[]而成，
INT []键）{
超（背景下，布局，dataCursor，从，到）;
this.dataCursor = dataCursor;
mInflater = LayoutInflater.from（上下文）;
}
公共查看getView（INT位置，查看convertView，ViewGroup中父）{
ViewHolder持有人;
如果（convertView == NULL）{
convertView = mInflater.inflate（R.layout.list_item，NULL）;
持有人=新ViewHolder（）;
holder.text1 =（TextView中）convertView.findViewById（R.id.label）;
holder.text2 =（TextView中）convertView.findViewById（R.id.listTitle）;
holder.text3 =（TextView中）convertView.findViewById（R.id.caption）;
convertView.setTag（保持器）;
} 其他 {
支架=（ViewHolder）convertView.getTag（）;
}
dataCursor.moveToPosition（位置）;
INT label_index = dataCursor.getColumnIndex（标签）;
字符串标签= dataCursor.getString（label_index）;
INT title_index = dataCursor.getColumnIndex（标题）;
字符串标题= dataCursor.getString（title_index）;
INT description_index = dataCursor.getColumnIndex（详细描述）;
字符串描述= dataCursor.getString（description_index）;
holder.text1.setText（标签）;
holder.text2.setText（职称）;
holder.text3.setText（介绍）;
返回convertView;
}
静态类ViewHolder {
TextView的文本1;
TextView的文本2;
TextView的文本3;
}
}
修订版：
更改displayResultList方法如下（工作）：
私人无效displayResultList（）{
如果（android.os.Environment.getExternalStorageState（）。等于（
android.os.Environment.MEDIA_MOUNTED））{
extStorageDirectory = Environment.getExternalStorageDirectory（）
的ToString（）;
文件DBFILE =新的文件（extStorageDirectory
+/Aero-Technologies/flyDroid/dB/flyDroid.db）;
SQLiteDatabase DB = SQLiteDatabase.openOrCreateDatabase（DBFILE，
空值）;
光标databaseCursor = db.rawQuery（SELECT * FROM AC_list，NULL）;
DomainAdapter databaseListAdapter =新DomainAdapter（这一点，
R.layout.list_item，databaseCursor，新的String [] {标签，
标题，说明}，新的INT [] {R.id.label，
R.id.listTitle，R.id.caption}）;
databaseListAdapter.notifyDataSetChanged（）;
this.setListAdapter（databaseListAdapter）;
}否则，如果（android.os.Environment.getExternalStorageState（）。等于（
android.os.Environment.MEDIA_UNMOUNTED））{
Log.i（标签，SD卡不可写/安装）;
Alerts.sdCardMissing（本）;
}
}
解决方案
我觉得你的问题是在
尝试{
db.rawQuery（SELECT * FROM AC_list，NULL）;
} 最后 {
如果（DB！= NULL）
Log.i（标签，DB封闭）;
db.close（）;
}
你，只要你查询关闭它和您的查询永远不会保存到databaseCursor，你想做的事，也许是什么：
尝试{
databaseCursor = db.rawQuery（SELECT * FROM AC_list，NULL）;
}赶上（例外五）{
如果（DB！= NULL）
Log.i（标签，DB封闭）;
db.close（）;
}
我希望这有助于
can someone see what I have wrong with my cursor: The data from the db is not returned (at least the screen is blank). I think that is my problem. In the DDMS shows it opens & closes the db. I am not sure what 'Cursor databaseCursor = null;' needs to be. Thnx!!
The Activity:
private void displayResultList() {
Cursor databaseCursor = null;
DomainAdapter databaseListAdapter = new DomainAdapter(this,
R.layout.list_item, databaseCursor, new String[] { "label",
"title", "description" }, new int[] { R.id.label,
R.id.listTitle, R.id.caption });
databaseListAdapter.notifyDataSetChanged();
this.setListAdapter(databaseListAdapter);
}
private void openAndQueryDatabase() {
if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_MOUNTED)) {
extStorageDirectory = Environment.getExternalStorageDirectory().toString();
File dbfile = new File(extStorageDirectory
+ "/Aero-Technologies/flyDroid/dB/flyDroid.db");
SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase(dbfile, null);
Log.i("tag", "db opened");
try {
db.rawQuery("SELECT * FROM AC_list", null);
} finally {
if (db != null)
Log.i("tag", "db closed");
db.close();
}
} else if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_UNMOUNTED)) {
Log.i("tag", "SDCard is NOT writable/mounted");
Alerts.sdCardMissing(this);
}
}
My Adapter:
public class DomainAdapter extends SimpleCursorAdapter{
private Cursor dataCursor;
private LayoutInflater mInflater;
public DomainAdapter(Context context, int layout, Cursor dataCursor, String[] from,
int[] to) {
super(context, layout, dataCursor, from, to);
this.dataCursor = dataCursor;
mInflater = LayoutInflater.from(context);
}
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item, null);
holder = new ViewHolder();
holder.text1 = (TextView) convertView.findViewById(R.id.label);
holder.text2 = (TextView) convertView.findViewById(R.id.listTitle);
holder.text3 = (TextView) convertView.findViewById(R.id.caption);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
dataCursor.moveToPosition(position);
int label_index = dataCursor.getColumnIndex("label");
String label = dataCursor.getString(label_index);
int title_index = dataCursor.getColumnIndex("title");
String title = dataCursor.getString(title_index);
int description_index = dataCursor.getColumnIndex("discription");
String description = dataCursor.getString(description_index);
holder.text1.setText(label);
holder.text2.setText(title);
holder.text3.setText(description);
return convertView;
}
static class ViewHolder {
TextView text1;
TextView text2;
TextView text3;
}
}
REVISED:
Change the displayResultList method to the following (working):
private void displayResultList() {
if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_MOUNTED)) {
extStorageDirectory = Environment.getExternalStorageDirectory()
.toString();
File dbfile = new File(extStorageDirectory
+ "/Aero-Technologies/flyDroid/dB/flyDroid.db");
SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase(dbfile,
null);
Cursor databaseCursor = db.rawQuery("SELECT * FROM AC_list", null);
DomainAdapter databaseListAdapter = new DomainAdapter(this,
R.layout.list_item, databaseCursor, new String[] { "label",
"title", "description" }, new int[] { R.id.label,
R.id.listTitle, R.id.caption });
databaseListAdapter.notifyDataSetChanged();
this.setListAdapter(databaseListAdapter);
} else if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_UNMOUNTED)) {
Log.i("tag", "SDCard is NOT writable/mounted");
Alerts.sdCardMissing(this);
}
}
解决方案
I think your problem is in
try {
db.rawQuery("SELECT * FROM AC_list", null);
} finally {
if (db != null)
Log.i("tag", "db closed");
db.close();
}
you are closing it as soon as you query and your query is never saved into databaseCursor, maybe what you wanted to do was:
try {
databaseCursor = db.rawQuery("SELECT * FROM AC_list", null);
} catch(Exception e) {
if (db != null)
Log.i("tag", "db closed");
db.close();
}
I hope this helps
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