Spinner reads data from the database and achieves Level 2 Interaction

This is mainly implemented here. The second-level association between provinces and cities. Select a province. Level 2 corresponds to all cities in the province

See the code below;
1. Activity
@ Override
Protected void oncreate (bundle savedinstancestate ){
// Todo auto-generated method stub
Super. oncreate (savedinstancestate );
Setcontentview (R. layout. test_layout );
This. mcontext = this;
Map <integer, list> DATA = provincedb. getprovince (); // obtain database data
Provincelist = data. Get (1 );
Provincedata = data. Get (0 );

Arrayadapter provinceadapter = new arrayadapter (mcontext, Android. R. layout. simple_spinner_item, provincelist );
Provinceadapter. setdropdownviewresource (Android. R. layout. simple_spinner_dropdown_item); // Style

Spprovince. setadapter (provinceadapter );
Spprovince. setonitemselectedlistener (itemselectedlistener );

}

// Select the province to associate with the target City
Private onitemselectedlistener itemselectedlistener = new onitemselectedlistener (){
@ Override
Public void onitemselected (adapterview <?> Parent, view,
Int position, long ID ){
Spinner spprovince = (spinner) parent;
String selprovince = (string) spprovince. getitematposition (position );
Arrayadapter cityadapter = NULL;
Map <string, integer> DATA = (MAP) provincedata. Get (position); // obtain the corresponding province id based on the selected province ID and then obtain the city
Int pid = data. Get (selprovince); // obtain the province ID
List citylist = provincedb. getcitybypid (PID );
Cityadapter = new arrayadapter (mcontext, Android. R. layout. simple_spinner_item, citylist );
Cityadapter
. Setdropdownviewresource (Android. R. layout. simple_spinner_dropdown_item );
Spcity. setadapter (cityadapter );
Spcity. setonitemselectedlistener (cityselectedlistener );

}

@ Override
Public void onnothingselected (adapterview <?> Parent ){
// Todo auto-generated method stub
}
};

String selectedcity = NULL;
Private onitemselectedlistener cityselectedlistener = new onitemselectedlistener (){
@ Override
Public void onitemselected (adapterview <?> Parent, view,
Int position, long ID ){
Spinner spcity = (spinner) parent;
Selectedcity = (string) spcity. getitematposition (position );
}

@ Override
Public void onnothingselected (adapterview <?> Parent ){
// Todo auto-generated method stub
}
};

2. DB-type query data

Public class provincedb {
Public static Map <integer, list> getprovince (){
String SQL = "select n_provid, s_provname from dict_province ";
Sqlitedatabase DB = NULL;
Cursor c = NULL;
Map <integer, list> provincedata = new hashmap <integer, list> ();
List provincelist = NULL;
Try {
DB = databasehelper. getdatabase ();
C = dB. rawquery (SQL, null );
List provincelist1 = new arraylist ();
List provincelist2 = new arraylist ();
While (C. movetonext ()){
Map provincemap = new hashmap ();
Provincemap. Put (C. getstring (1), C. getint (0 ));
Provincelist1.add (provincemap );
Provincelist2.add (C. getstring (1 ));
}
Provincedata. Put (0, provincelist1 );
Provincedata. Put (1, provincelist2 );
} Catch (exception e ){
E. printstacktrace ();
} Finally {
If (C! = NULL ){
C. Close ();
}
If (DB! = NULL ){
DB. Close ();
}
}
Return provincedata;
}

Public static list <string> getcitybypid (int id ){
String SQL = "select s_cityname from dict_city where n_provid =" + ID;
Sqlitedatabase DB = NULL;
Cursor c = NULL;
List <string> citylist = NULL;
Try {
DB = databasehelper. getdatabase ();
C = dB. rawquery (SQL, null );
Citylist = new arraylist <string> ();
While (C. movetonext ()){
Citylist. Add (C. getstring (0 ));
}
} Catch (exception ex ){
Ex. printstacktrace ();
} Finally {
If (C! = NULL ){
C. Close ();
}
If (DB! = NULL ){
DB. Close ();
}
}
Return citylist;

}
}

3. test_layout.xml
<? XML version = "1.0" encoding = "UTF-8"?>
<Linearlayout xmlns: Android = "http://schemas.android.com/apk/res/android"
Android: layout_width = "fill_parent" Android: layout_height = "fill_parent"
Android: Orientation = "vertical">

<Linearlayout Android: layout_width = "fill_parent"
Android: layout_height = "wrap_content">
<Spinner Android: Id = "@ + ID/sp_bslprovice" Android: layout_width = "wrap_content"
Android: layout_height = "wrap_content" Android: layout_weight = "1"/>
<Spinner Android: Id = "@ + ID/sp_bslcity" Android: layout_width = "wrap_content"
Android: layout_height = "wrap_content" Android: layout_weight = "1"/>
</Linearlayout>