android对数据库的增删改查操作

      当应用程序需要处理的数据量比较大时，为了方便对数据的管理，通常需要使用数据库来存储数据。

package com.example.sample7_5;import android.app.Activity;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;public class MainActivity extends Activity {private SQLiteDatabase sld;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);InitViews();}private void InitViews() {Button b = (Button) findViewById(R.id.Button01);b.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {createOrOpenDatabase();//创建数据库}});b = (Button) findViewById(R.id.Button02);b.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {closeDatabase();//关闭数据库}});b = (Button) findViewById(R.id.Button03);b.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {insert();//添加记录}});b = (Button) findViewById(R.id.Button04);b.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {delete();//删除记录}});b = (Button) findViewById(R.id.Button05);b.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {update();//更新记录}});b = (Button) findViewById(R.id.Button06);b.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {query();//查询记录}});}protected void query() {try {String sql = "select * from student where sage>?";Cursor cur = sld.rawQuery(sql, new String[]{"20"});appendMessage("学号\t\t姓名\t\t年龄\t班级");while(cur.moveToNext()){String sno = cur.getString(0);String sname = cur.getString(1);int sage = cur.getInt(2);String sclass = cur.getString(3);appendMessage(sno+"\t"+sname+"\t\t"+sage+"\t"+sclass);}cur.close();} catch (Exception e) {Toast.makeText(MainActivity.this, "数据库错误："+e.toString(), Toast.LENGTH_SHORT).show();e.printStackTrace();}}protected void update() {try {String sql = "update student set stuname='李勇'";sld.execSQL(sql);appendMessage("成功更新记录");} catch (Exception e) {Toast.makeText(MainActivity.this, "数据库错误："+e.toString(), Toast.LENGTH_SHORT).show();e.printStackTrace();}}protected void delete() {try {String sql = "delete from student;";sld.execSQL(sql);appendMessage("成功删除所有记录");} catch (Exception e) {Toast.makeText(MainActivity.this, "数据库错误："+e.toString(), Toast.LENGTH_SHORT).show();e.printStackTrace();}}protected void insert() {try {String sql = "insert into student values('10001','王强', 23, '97002')";sld.execSQL(sql);appendMessage("成功插入一条记录");} catch (Exception e) {Toast.makeText(MainActivity.this, "数据库错误："+e.toString(), Toast.LENGTH_SHORT).show();e.printStackTrace();}}protected void closeDatabase() {sld.close();}protected void createOrOpenDatabase() {try {sld = SQLiteDatabase.openDatabase("/data/data/com.example.sample7_5/mydb", null, SQLiteDatabase.OPEN_READWRITE|SQLiteDatabase.CREATE_IF_NECESSARY);appendMessage("数据库已经成功打开");String sql = "create table if not exists student(sno char(5), stuname varchar(20), sage integer, sclass char(5))";sld.execSQL(sql);appendMessage("student 已经成功创建!");} catch (Exception e) {Toast.makeText(MainActivity.this, "数据库错误："+e.toString(), Toast.LENGTH_SHORT).show();e.printStackTrace();}}private void appendMessage(String message) {EditText et = (EditText) findViewById(R.id.EditText01);et.append(message+"\n");;}}

如果想借用代码，需要改动的就是创建数据库的位置，即改动下面的代码即可。

sld = SQLiteDatabase.openDatabase("/data/data/com.example.sample7_5/mydb", null, SQLiteDatabase.OPEN_READWRITE|SQLiteDatabase.CREATE_IF_NECESSARY);

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