久违了，我又开始写代码了，几天后我的代码仍然有问题。
我的应用程序中有一个预填充的数据库，其中包含两个表。第一个用于第一个活动（AllEnglandList）并显示一个列表。单击该列表中的一行时，会从第二个表中的数据中调出第二个列表视图 Activity (AllTrails)。为此，我使用了 .putExtra 并且效果很好。
单击此列表中的一行时，我试图使用单击行中的字符串从我的数据库中调用特定单元格。因此，例如，如果单击 Apple，它将查看我的数据库中的 FruitName 列，并查看哪一行包含 Apple。然后它将读取该行并返回 Column FruitDescription 的内容。
目前，单击时我得到一个空白活动（AllEnglandList）。
这是我的助手
class AllEnglandHelper extends SQLiteOpenHelper {
// we declare a bunch of useful constants
// they should be pretty obvious what they are!
private static final String DATABASE_PATH = "/data/data/com.wills.master/databases/";
private static final String DATABASE_NAME = "Fruit.db";
private static final int SCHEMA_VERSION = 1;
public static final String TABLE_NAME = "Databasing_Index";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_TITLE = "ObjectIndex";
// BE AWARE - if you make changes to your database using sqlitebrower, you
// will need to refresh the assets folder in eclipse
public static final String SECOND_TABLE_NAME = "Databasing_Details";
public static final String SECOND_COLUMN_ID = "_id";
public static final String SECOND_COLUMN_TITLE = "ObjectName";
public static final String SECOND_COLUMN_TITLE2 = "ObjectDescription";
public SQLiteDatabase dbSqlite;
private final Context myContext;
public AllEnglandHelper(Context context) {
super(context, DATABASE_NAME, null, SCHEMA_VERSION);
this.myContext = context;
// check if exists and copy database from resource
// createDB();
}
@Override
public void onCreate(SQLiteDatabase db) {
// check if exists and copy database from resource
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public void createDatabase() {
createDB();
}
private void createDB() {
boolean dbExist = DBExists();
if (!dbExist) {
// By calling the method we create an empty database into the
// default system location
// We need this so we can overwrite that database with our database
this.getReadableDatabase();
// now we copy the database we included!
copyDBFromResource();
}
}
private boolean DBExists() {
SQLiteDatabase db = null;
try {
String databasePath = DATABASE_PATH + DATABASE_NAME;
db = SQLiteDatabase.openDatabase(databasePath, null,
SQLiteDatabase.OPEN_READWRITE);
db.setLocale(Locale.getDefault());
db.setLockingEnabled(true);
db.setVersion(1);
} catch (SQLiteException e) {
Log.e("SqlHelper", "database not found");
}
if (db != null) {
db.close();
}
return db != null ? true : false;
}
private void copyDBFromResource() {
InputStream inputStream = null;
OutputStream outStream = null;
String dbFilePath = DATABASE_PATH + DATABASE_NAME;
try {
inputStream = myContext.getAssets().open(DATABASE_NAME);
outStream = new FileOutputStream(dbFilePath);
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) > 0) {
outStream.write(buffer, 0, length);
}
outStream.flush();
outStream.close();
inputStream.close();
} catch (IOException e) {
throw new Error("Problem copying database from resource file.");
}
}
public void openDataBase() throws SQLException {
String myPath = DATABASE_PATH + DATABASE_NAME;
dbSqlite = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
}
@Override
public synchronized void close() {
if (dbSqlite != null) {
dbSqlite.close();
}
super.close();
}
// the following two methods return the column you want and it's title
// (getName)
public Cursor getCursor() {
SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
queryBuilder.setTables(TABLE_NAME);
String[] asColumnsToReturn = new String[] { COLUMN_ID, COLUMN_TITLE };
// make sure you get your search pass correctly!
Cursor mCursor = queryBuilder.query(dbSqlite, asColumnsToReturn, null,
null, null, null, "_id");
// the name after the nulls dictates how the results are returned. ie in
// order of "column name"
return mCursor;
}
public String getName(Cursor c) {
return (c.getString(1));
// where 1 refers to COLUMN_TITLE line 11 rows above (0 would be
// COLUMN_ID and so on)
}
public Cursor getTrailByType(String id) {
String[] args = {id};
return (getReadableDatabase()
.rawQuery("SELECT _id, ObjectName FROM Databasing_Details WHERE Index_id=?", args));
}
public Cursor getTrailByDetails(String id) {
String[] args = {id};
return (getReadableDatabase()
.rawQuery("SELECT _id, ObjectDescription FROM Databasing_Details WHERE ObjectName=?", args));
}
}
第一个活动
public class AllEnglandList extends Activity {
// we use a string to hold the name of our extra,
// it must include the full package name
public final static String ID_EXTRA = "com.wills.master._ID";
private AllEnglandHelper dbDataBaseHelper = null;
private Cursor ourCursor = null;
private DataBaseAdapter adapter = null;
@Override
public void onCreate(Bundle savedInstanceState) {
try {
super.onCreate(savedInstanceState);
setContentView(R.layout.trail_list);
// this is our ListView element, obtained by id from our XML Layout
ListView myListView = (ListView) findViewById(R.id.list_view);
// create our database Helper
dbDataBaseHelper = new AllEnglandHelper(this);
// we call the create right after initializing the helper, just in
// case
// they have never run the app before
dbDataBaseHelper.createDatabase();
//
// open the database!! Our helper now has a SQLiteDatabase database
// object
dbDataBaseHelper.openDataBase();
// get our cursor. A cursor is a pointer to a dataset, in this case
// a set of results from a database query
ourCursor = dbDataBaseHelper.getCursor();
// tell android to start managing the cursor
// we do this just incase our activity is interrupted or ends, we
// want the activity
// to close and deactivate the cursor, as needed
startManagingCursor(ourCursor);
// create our adapter
adapter = new DataBaseAdapter(ourCursor);
// set the adapter!!!
myListView.setAdapter(adapter);
// this is how we know what to do when a list item is clicked
myListView.setOnItemClickListener(onListClick);
} catch (Exception e) {
// this is the line of code that sends a real message to the Log
Log.e("ERROR", "ERROR IN CODE: " + e.toString());
// this is the line that prints out the location
// the code where the error occurred.
e.printStackTrace();
}
}
private AdapterView.OnItemClickListener onListClick = new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
// Create our intent, as per usual
Intent i = new Intent(AllEnglandList.this, AllTrails.class);
i.putExtra(ID_EXTRA, String.valueOf(id));
startActivity(i);
}
};
class DataBaseAdapter extends CursorAdapter {
DataBaseAdapter(Cursor c) {
super(AllEnglandList.this, c);
}
@Override
// this is a CursorAdapter
// instead of Using a getView and if(row=null)
// we use a bindView and newView calls
// we can get away with this because CursorAdapters have
// a default implementation of getView that calls bindView and newView
// as needed. This makes our code a bit cleaner, and is the better way
// to
// do this
public void bindView(View row, Context ctxt, Cursor c) {
DataBaseHolder holder = (DataBaseHolder) row.getTag();
holder.populateFrom(c, dbDataBaseHelper);
}
@Override
public View newView(Context ctxt, Cursor c, ViewGroup parent) {
LayoutInflater inflater = getLayoutInflater();
View row = inflater.inflate(R.layout.trail_list, parent, false);
DataBaseHolder holder = new DataBaseHolder(row);
row.setTag(holder);
return (row);
}
}
static class DataBaseHolder {
private TextView name = null;
DataBaseHolder(View row) {
name = (TextView) row.findViewById(R.id.row);
}
void populateFrom(Cursor c, AllEnglandHelper r) {
name.setText(r.getName(c));
}
}
}
第二次活动
public class AllTrails extends Activity{
String passedVar=null;
boolean passedVar1=false;
public final static String ID_EXTRA = "com.wills.master._ID";
private AllEnglandHelper dbTrailTypeHelper = null;
private Cursor ourCursor = null;
private TrailAdapter adapter=null;
public void onCreate(Bundle savedInstanceState) {
try {
super.onCreate(savedInstanceState);
setContentView(R.layout.trail_list);
//Get our passed variable from our intent's EXTRAS
passedVar=getIntent().getStringExtra(AllEnglandList.ID_EXTRA);
//this is our ListView element, obtained by id from our XML layout
ListView myListView = (ListView)findViewById(R.id.list_view);
String string = passedVar;
int passedInt = Integer.parseInt(string);
if (passedInt==1) { passedVar1 = true;
}
//create our database Helper
dbTrailTypeHelper=new AllEnglandHelper(this);
//a set of results from a database query
ourCursor=dbTrailTypeHelper.getTrailByType(passedVar);
//tell android to start managing the cursor,
//we do this just incase our activity is interrupted or ends, we want the activity
//to close and deactivate the cursor, as needed
startManagingCursor(ourCursor);
//create our adapter
adapter=new TrailAdapter(ourCursor);
//set the adapter!!!
myListView.setAdapter(adapter);
myListView.setOnItemClickListener(onListClick);
} catch (Exception e) {
// this is the line of code that sends a real message to the Log
Log.e("ERROR", "ERROR IN CODE: " + e.toString());
// this is the line that prints out the location
// the code where the error occurred.
e.printStackTrace();
}
}
private AdapterView.OnItemClickListener onListClick = new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
// Create our intent, as per usual
Intent i = new Intent(AllTrails.this, AllEnglandTrails.class);
i.putExtra(ID_EXTRA, String.valueOf(id));
startActivity(i);
}
};
class TrailAdapter extends CursorAdapter {
TrailAdapter(Cursor c) {
super(AllTrails.this, c);
}
@Override
//this is a CusorAdapter
//instead of Using a getView and if(row==null)
// we use bindView and newView calls
//we can get away with this because CursorAdapters have
//a default implementation of getView that calls bindView and newView
//as needed. This makes our code a bit cleaner, and is the better way to
//do this.
public void bindView(View row, Context ctxt,
Cursor c) {
TrailTypeHolder holder=(TrailTypeHolder)row.getTag();
holder.populateFrom(c, dbTrailTypeHelper);
}
@Override
public View newView(Context ctxt, Cursor c, ViewGroup parent) {
LayoutInflater inflater=getLayoutInflater();
View row=inflater.inflate(R.layout.trail_list, parent, false);
TrailTypeHolder holder=new TrailTypeHolder(row);
row.setTag(holder);
return(row);
}
}
static class TrailTypeHolder {
private TextView name=null;
TrailTypeHolder(View row) {
name=(TextView)row.findViewById(R.id.row);
}
void populateFrom(Cursor c, AllEnglandHelper r) {
name.setText(r.getName(c));
}
}
}
第三次活动
public class AllTrails extends Activity{
String passedVar=null;
boolean passedVar1=false;
public final static String ID_EXTRA = "com.wills.master._ID";
private AllEnglandHelper dbTrailTypeHelper = null;
private Cursor ourCursor = null;
private TrailAdapter adapter=null;
public void onCreate(Bundle savedInstanceState) {
try {
super.onCreate(savedInstanceState);
setContentView(R.layout.trail_list);
//Get our passed variable from our intent's EXTRAS
passedVar=getIntent().getStringExtra(AllEnglandList.ID_EXTRA);
//this is our ListView element, obtained by id from our XML layout
ListView myListView = (ListView)findViewById(R.id.list_view);
String string = passedVar;
int passedInt = Integer.parseInt(string);
if (passedInt==1) { passedVar1 = true;
}
//create our database Helper
dbTrailTypeHelper=new AllEnglandHelper(this);
//a set of results from a database query
ourCursor=dbTrailTypeHelper.getTrailByType(passedVar);
//tell android to start managing the cursor,
//we do this just incase our activity is interrupted or ends, we want the activity
//to close and deactivate the cursor, as needed
startManagingCursor(ourCursor);
//create our adapter
adapter=new TrailAdapter(ourCursor);
//set the adapter!!!
myListView.setAdapter(adapter);
myListView.setOnItemClickListener(onListClick);
} catch (Exception e) {
// this is the line of code that sends a real message to the Log
Log.e("ERROR", "ERROR IN CODE: " + e.toString());
// this is the line that prints out the location
// the code where the error occurred.
e.printStackTrace();
}
}
private AdapterView.OnItemClickListener onListClick = new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
// Create our intent, as per usual
Intent i = new Intent(AllTrails.this, AllEnglandTrails.class);
i.putExtra(ID_EXTRA, passedVar);
startActivity(i);
}
};
class TrailAdapter extends CursorAdapter {
TrailAdapter(Cursor c) {
super(AllTrails.this, c);
}
@Override
//this is a CusorAdapter
//instead of Using a getView and if(row==null)
// we use bindView and newView calls
//we can get away with this because CursorAdapters have
//a default implementation of getView that calls bindView and newView
//as needed. This makes our code a bit cleaner, and is the better way to
//do this.
public void bindView(View row, Context ctxt,
Cursor c) {
TrailTypeHolder holder=(TrailTypeHolder)row.getTag();
holder.populateFrom(c, dbTrailTypeHelper);
}
@Override
public View newView(Context ctxt, Cursor c, ViewGroup parent) {
LayoutInflater inflater=getLayoutInflater();
View row=inflater.inflate(R.layout.trail_list, parent, false);
TrailTypeHolder holder=new TrailTypeHolder(row);
row.setTag(holder);
return(row);
}
}
static class TrailTypeHolder {
private TextView name=null;
TrailTypeHolder(View row) {
name=(TextView)row.findViewById(R.id.row);
}
void populateFrom(Cursor c, AllEnglandHelper r) {
name.setText(r.getName(c));
}
}
}
我进行了多次搜索，但没有找到任何专门处理此问题的内容。