c#-winform-three-level linkage

Three-level linkage-Query the region, select the province to automatically show the province's cities, counties

Like the next database

　　

First, write the Query method

 Public classChinadata {SqlConnection conn=NULL; SqlCommand cmd=NULL;  PublicChinadata () {conn=NewSqlConnection ("server=.; Database=mydb;user=sa;pwd=123"); CMD=Conn.        CreateCommand (); }        //Query method parameters are parent code         PublicList<china> Select (stringPcode) {List<China> LC =NewList<china>(); Cmd.commandtext="Select *from chinastates where [email protected]"; Cmd.            Parameters.clear (); Cmd. Parameters.addwithvalue ("@a", Pcode); Conn.            Open (); SqlDataReader Dr=cmd.            ExecuteReader (); if(Dr. HasRows) { while(Dr. Read ()) {China C=NewChina (); C.areacode= dr["AreaCode"].                    ToString (); C.areaname= dr["AreaName"].                    ToString (); C.parentareacode= dr["Parentareacode"].                    ToString (); Lc.                ADD (c); }} conn.            Close (); returnLC; }    }

Query Method

Second, automatically read the database data when the form starts

  Public Partial classForm1:form { PublicForm1 () {InitializeComponent (); //when the window opens, automatic query Code 0001 sub-level data in China//Binding ProvinceCombobox1.datasource =NewChinadata (). Select ("0001"); Combobox1.displaymember="AreaName"; Combobox1.valuemember="AreaCode"; //Binding CityCombobox2.datasource =NewChinadata ().            Select (ComboBox1.SelectedValue.ToString ()); Combobox2.displaymember="AreaName"; Combobox2.valuemember="AreaCode"; //Bound CountiesCombobox3.datasource =NewChinadata ().            Select (ComboBox2.SelectedValue.ToString ()); Combobox3.displaymember="AreaName"; Combobox3.valuemember="AreaCode"; }    }

automatically read database data when form starts

Third, the implementation of change options, the presentation of sub-level content

//event When selected item is changed by province        Private voidComboBox1_SelectedIndexChanged (Objectsender, EventArgs e) {            //Binding CityCombobox2.datasource =NewChinadata ().            Select (ComboBox1.SelectedValue.ToString ()); Combobox2.displaymember="AreaName"; Combobox2.valuemember="AreaCode"; }        //event when the city selection changes        Private voidCombobox2_selectedindexchanged_1 (Objectsender, EventArgs e) {            //Bound CountiesCombobox3.datasource =NewChinadata ().            Select (ComboBox2.SelectedValue.ToString ()); Combobox3.displaymember="AreaName"; Combobox3.valuemember="AreaCode"; }

achieve two-level linkage, three-level linkage

Complete Regional selection

c#-winform-three-level linkage