Android 数据库增删改查
文章目录
一、案例演示
二、实现步骤
1、activity_main.xml
页面布局
代码
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:id="@+id/tv_username"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="30sp"
android:layout_marginTop="10dp"
android:text="用户名："/>
<EditText
android:id="@+id/et_username"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:layout_toRightOf="@id/tv_username"
android:minLines="2" />
<EditText
android:id="@+id/et_password"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@id/et_username"
android:layout_alignLeft="@id/et_username"
android:layout_marginTop="10dp"
android:inputType="textPassword"
android:minLines="2"
android:textSize="30sp" />
<TextView
android:id="@+id/tv_choiceB"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@id/et_password"
android:textSize="30sp"
android:text="密 码："/>
<EditText
android:id="@+id/et_age"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@id/et_password"
android:layout_alignLeft="@id/et_password"
android:layout_marginTop="10dp"
android:minLines="2" />
<TextView
android:id="@+id/tv_age"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@id/et_age"
android:textSize="30sp"
android:text="年 龄："/>
<Button
android:id="@+id/bt_save"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/tv_age"
android:layout_alignTop="@id/bt_query"
android:text="保存"
android:textSize="25sp" />
<Button
android:id="@+id/bt_update"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="修改"
android:layout_toRightOf="@id/bt_query"
android:layout_below="@id/et_age"
android:layout_marginTop="10dp"
android:layout_marginLeft="10dp"
android:textSize="25sp"
/>
<Button
android:id="@+id/bt_delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="删除"
android:layout_toRightOf="@id/bt_update"
android:layout_below="@id/et_age"
android:layout_marginTop="10dp"
android:layout_marginLeft="10dp"
android:textSize="25sp"
/>
<Button
android:id="@+id/bt_query"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/et_age"
android:layout_marginLeft="10dp"
android:layout_marginTop="10dp"
android:layout_toRightOf="@id/bt_save"
android:text="查询"
android:textSize="25sp" />
<TextView
android:id="@+id/tv_show"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/bt_save"
android:textSize="25dp" />
</RelativeLayout>
2、MainActivity.java
通过点击不同的按钮，进行不同的增删改查操作
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private SQLiteOpenHelper helper;
private UserDao userDao;
private User user;
private EditText et_username,et_password,et_age;
private Button bt_save,bt_query,bt_update,bt_delete;
private TextView tv_show;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//初始化
init();
userDao=new UserDao(this);
}
public void init(){
et_username = findViewById(R.id.et_username);
et_password = findViewById(R.id.et_password);
et_age = findViewById(R.id.et_age);
bt_save = findViewById(R.id.bt_save);
bt_query = findViewById(R.id.bt_query);
bt_update = findViewById(R.id.bt_update);
bt_delete = findViewById(R.id.bt_delete);
tv_show = findViewById(R.id.tv_show);
bt_save.setOnClickListener(this);
bt_query.setOnClickListener(this);
bt_update.setOnClickListener(this);
bt_delete.setOnClickListener(this);
}
@Override
public void onClick(View view) {
switch (view.getId()){
case R.id.bt_save:{
user=new User(et_username.getText().toString(),et_password.getText().toString(),Integer.parseInt((et_age.getText().toString())));
long i=userDao.addUser(user);
if(i!=-1){
Toast.makeText(this, "添加成功", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(this, "添加失败", Toast.LENGTH_SHORT).show();
}
break;
}
case R.id.bt_delete:{
int i= userDao.deleteUser(et_username.getText().toString());
if(i!=0){
Toast.makeText(this, "删除成功", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(this, "删除失败", Toast.LENGTH_SHORT).show();
}
break;
}
case R.id.bt_update:{
user=new User(et_username.getText().toString(),et_password.getText().toString(),Integer.parseInt((et_age.getText().toString())));
int i= userDao.updateUser(user);
if(i!=0){
Toast.makeText(this, "修改成功", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(this, "修改失败", Toast.LENGTH_SHORT).show();
}
break;
}
case R.id.bt_query:{
//为了解决查询重复问题，需要先创建一个StringBuffer或者String类型对象，用于存储数据，存储后在给控件赋值就可以解决
ArrayList list=userDao.queryAll();
StringBuffer buffer=new StringBuffer();
if(list.size()==0){
tv_show.setText("没有数据");
}else {
for (int i=0;i<list.size();i++){
User user= (User) list.get(i);
buffer.append("id:" +user.getId()+
"用户名:"+user.getUsername()+
"密码:"+user.getPassword()+
"年龄:"+user.getAge()+"n");
}
tv_show.setText(buffer);
}
break;
}
}
}
}
3、UserDao.java
包含对数据库的增删改查方法
public class UserDao {
private SQLiteOpenHelper helper;
public UserDao(Context context){
helper=new SQLiteOpenHelper(context,"user1",null,1);
}
//添加数据
public long addUser(User user){
//1.获取数据库对象
SQLiteDatabase database=helper.getWritableDatabase();
//那些列为空，可以设置为空
ContentValues values=new ContentValues();
//key是数据表的列名，value是要放进去的值
values.put("username",user.getUsername());
values.put("password",user.getPassword());
values.put("age",user.getAge());
//第一个参数表明，第二个参数自动赋值为null的列名，第三个参数数据
//返回值long,插入成功行号，插入失败-1
long i=database.insert("users",null,values);
//关闭数据库
database.close();
return i;
}
//删除
public int deleteUser(String username){
//1.获取数据库对象
SQLiteDatabase database=helper.getWritableDatabase();
//第一个参数表明，第二个参数为删除条件，第三个参数为第二个参数中占位符所需值组成的字符串数组
int i=database.delete("users","username=?",new String[]{username+""});
//关闭数据库
database.close();
return i;
}
//修改
public int updateUser(User user){
//1.获取数据库对象
SQLiteDatabase database=helper.getWritableDatabase();
//那些列为空，可以设置为空
ContentValues values=new ContentValues();
//key是数据表的列名，value是要放进去的值
values.put("username",user.getUsername());
values.put("password",user.getPassword());
values.put("age",user.getAge());
//第一个参数表明，第二个参数新数据，第三个参数是条件
int i=database.update("users",values,"username=?",new String[]{user.getUsername()});
//关闭数据库
database.close();
return i;
}
//查询
public ArrayList queryAll(){
ArrayList list=new ArrayList();
SQLiteDatabase database=helper.getWritableDatabase();
Cursor cursor=database.query("users",null,null,null,null,null,null);
list=convertFromCursor(cursor);
return list;
}
//通过对Cursor对象遍历查询结果，并将其范围为一个list集合
private ArrayList convertFromCursor(Cursor cursor){
ArrayList list=new ArrayList();
if(cursor!=null&&cursor.moveToFirst()){
//通过游标遍历这个集合
do{
int id=cursor.getInt(cursor.getColumnIndex("id"));
String username=cursor.getString(cursor.getColumnIndex("username"));
String password=cursor.getString(cursor.getColumnIndex("password"));
int age=cursor.getInt(cursor.getColumnIndex("age"));
User user=new User(id,username,password,age);
list.add(user);
}while (cursor.moveToNext());
}
return list;
}
}
4、User.java
实体类对应着user表中的字段
public class User {
private int id;
private String username;
private String password;
private int age;
public User(int id, String username, String password, int age) {
this.id = id;
this.username = username;
this.password = password;
this.age = age;
}
public User(String username, String password, int age) {
this.username = username;
this.password = password;
this.age = age;
}
public User(){};
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
5、SQLiteOpenHelper.java
创建表，更新表方法
public class SQLiteOpenHelper extends android.database.sqlite.SQLiteOpenHelper {
private Context context;
public static final String CREATE_TABLES="create table users ("+
"id integer primary key autoincrement,"+
"username text,"+
"password text,"+
"age integer)";
public static final String CREATE_DEPARTMENT="create table department ("+
"id integer primary key autoincrement,"+
"departmentName text,"+
"departCode text)";
public SQLiteOpenHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
this.context=context;
}
//创建数据表(只有在第一次创建数据库的时候才会被调用)
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
sqLiteDatabase.execSQL(CREATE_TABLES);
Toast.makeText(context, "success databases", Toast.LENGTH_SHORT).show();
}
//数据库的更新（第一个参数数据库对象，第二个参数旧版本号，第三个参数新版本号）
//新版本号大于旧版本号就会调用onUpgrade方法
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
/**
* //如果数据表存在就删除
* sqLiteDatabase.execSQL("drop table if exists users");
* sqLiteDatabase.execSQL("drop table if exists department");
* onCreate(sqLiteDatabase);
*/
switch (i){
case 1:sqLiteDatabase.execSQL(CREATE_DEPARTMENT);
}
}
}