Android makes SQLite table by reflection

Last Update:2015-07-17 Source: Internet

Author: User

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1. We write a dbhelper inherited from Sqliteopenhelper<pre> public classDBHelperextendssqliteopenhelper{//version of the database Private Final Static intDb_version = 1; //Database name Private Final StaticString db_name = "ladeng.db"; PrivateContext mcontext; //we call the constructor of the parent class directly with super, so that we only need to pass in a context parameter when we instantiate the Dbhelper. publicdbhelper (context Context) {Super(context, db_name,NULL, db_version); this. Mcontext =context; } //This method is called when the database does not exist.@Override public voidonCreate (sqlitedatabase db) {createtables (db,0,0); } //call this method when the version number is changed@Override public voidOnupgrade (sqlitedatabase db,intoldversion,intNewversion) { //1. Delete the original table//2. Call OnCreate to re-create the database } /*** Build a table statement, you can build a table in just one row*/ Private voidCreatetables (sqlitedatabase db,intoldversion,intNewversion) { //createtable (movie.class) returns the SQL Build table statement//Db.execsql (sql) executes this build statementDb.execsql (createtable (Movie.class)); } /*** If not, the default is to use class masterpieces to indicate *@paramClazz entity class *@return */ Private<T> String createtable (class<t>Clazz) { returncreatetable (clazz, clazz.getsimplename ()); } /*** The real way to build a table *@paramClazz entity class *@paramTableName indicates *@returnSQL Build Table statement*/ Private<T> String createtable (class<t>clazz, String TableName) { //instantiate a container that is used to stitch SQL statementsStringBuffer Sbuffer =NewStringBuffer (); //SQL statement, The first field is _id primary key auto-increment, This is universal, so write directly to the deadSbuffer.append ("create Table if not exists" + tableName + "+" (_id INTEGER PRIMARY KEY AutoIncrement not NULL, "); //get all the public properties in the entity classfield[] fields =Clazz.getfields (); //Traverse all of the public properties for(Field Field:fields) {//if the property is not _id, the description is a new field if(!field.getname (). equals ("_id")) { //get the basic data type of the propertyString type =field.gettype (). getsimplename (); //if the property is of type string, set the field type to text if(type.equals ("String") {sbuffer.append (field.getname () )+ "TEXT,"); //If the attribute is of type int, set the field type to integer}Else if(type.equals ("int") {sbuffer.append (field.getname () )+ "INTEGER,"); } } } //remove the last commaSbuffer.deletecharat (sbuffer.length ()-1); //replacement); Indicates the end of the SQL statementSbuffer.append (");"); //return this SQL statement returnsbuffer.tostring (); } }</pre>2.Movie entity class, the attribute in the entity class is the field in the table<pre><pre> public class Movie { public String title; public int rating; public String year; public String genre; public String country; public int price ;}</pre></pre>3. Add the following code to the Mainactivity.java<pre><pre> public class mainactivity extends Activity {@Override protected void onCreate (Bundle Savedinstancestate { super .oncreate (savedinstancestate) ; Setcontentview (r.layout.activity_main); // Instantiate our dbhelper dbhelper DBHelper = new dbhelper (this ); // DBHelper in OnCreate does not execute until this method is called dbhelper.getreadabledatabase (); }}</pre> </pre>4. We check whether the table has been built in the Data/data/package name/databases/ladeng.dbAndroid makes SQLite table by reflection

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Android makes SQLite table by reflection

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