快速格式化代码：ctrl+alt+l
1. SQList 方式存储数据数据
关键一：监听器过多的情况下如何优化代码。
1.1 添加数据
1. 用db.insert方法
case R.id.add:
//获取数据库对象
db = myDbHelper.getWritableDatabase();
String uname = et_uname.getText().toString();
String upwd = et_upwd.getText().toString();
//创建一个ContentValues对象用于存储记录的字段值;
// 以键值对存储，键对应字段名，值是字段的具体值
ContentValues contentValues=new ContentValues();
// contentValues.put("userId",1);//因为是自增长所以可以不用写
contentValues.put("userName",uname);
contentValues.put("password",upwd);
db.insert("az_user",null,contentValues);
2. 用db.execSQL方法
一行搞定
//创建一个ContentValues对象用于存储记录的字段值;
// 以键值对存储，键对应字段名，值是字段的具体值
// ContentValues contentValues=new ContentValues();
//// contentValues.put("userId",1);//因为是自增长所以可以不用写
// contentValues.put("userName",uname);
// contentValues.put("password",upwd);
// db.insert("az_user",null,contentValues);
db.execSQL("insert into az_user(userName,password) values(?,?)", new Object[]{uname,upwd});
1.2 查询
1.2.1 查询所有1用query查询
db = myDbHelper.getWritableDatabase();
//Cursor：结果集，结果集中会有游标指向结果集中的某一条记录。
Cursor cursor = db.query("az_user",new String[]{"userName","password"},null,null,null,null,null,null);
cursor.moveToFirst();
showInfo.setText("用户名："+cursor.getString(0)+",密码："+cursor.getString(1));
while(cursor.moveToNext()){
showInfo.append("\n"+"用户名："+cursor.getString(0)+",密码："+cursor.getString(1));
}
cursor.close();
db.close();
1.2.1 条件查询1用query查询
case R.id.generate:
db=myDbHelper.getWritableDatabase();
String selection = et_selection.getText().toString();
Cursor cursor1 = db.query("az_user",new String[]{"userName","password"},"userName=?",new String[] {selection},null,null,null,null);
showInfo.setText("查询结果如下：");
while(cursor1.moveToNext()){
showInfo.append("\n"+"用户名："+cursor1.getString(0)+"密码："+cursor1.getString(1));
}
cursor1.close();
db.close();
1.2.2 条件查询2用rawQuery查询
case R.id.generate:
db=myDbHelper.getWritableDatabase();
String selection = et_selection.getText().toString();
// Cursor cursor1 = db.query("az_user",new String[]{"userName","password"},"userName=?",new String[] {selection},null,null,null,null);
Cursor cursor1=db.rawQuery("select userName,password from az_user where userName=?",new String[]{selection});
showInfo.setText("查询结果如下：");
while(cursor1.moveToNext()){
showInfo.append("\n"+"用户名："+cursor1.getString(0)+"密码："+cursor1.getString(1));
}
cursor1.close();
db.close();
1.3 删除
1.3.1 通过delete方法
db = myDbHelper.getWritableDatabase();
String selection1 = et_selection.getText().toString();
int i=db.delete("az_user","userName=?",new String[]{selection1});
if(i>0){
Toast.makeText(MainActivity.this,"删除成功,删除了"+i+"条",Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(MainActivity.this,"删除失败",Toast.LENGTH_SHORT).show();
}
db.close();
1.3.2 通过execSQL方法
注意只能操作，不能返回删掉了几条。
case R.id.delete:
db = myDbHelper.getWritableDatabase();
String selection1 = et_selection.getText().toString();
// int i=db.delete("az_user","userName=?",new String[]{selection1});
db.execSQL("delete from az_user where userName=?",new Object[]{selection1});
// if(i>0){
// Toast.makeText(MainActivity.this,"删除成功,删除了"+i+"条",Toast.LENGTH_SHORT).show();
// }else{
// Toast.makeText(MainActivity.this,"删除失败",Toast.LENGTH_SHORT).show();
// }
db.close();
break;
1.4 修改
用update实现
case R.id.update:
db = myDbHelper.getWritableDatabase();
String username1 = et_uname.getText().toString();
String password1 =et_upwd.getText().toString();
String selection2=et_selection.getText().toString();
ContentValues contentValues=new ContentValues();
contentValues.put("userName",username1);
contentValues.put("password",password1);
db.update("az_user",contentValues,"userName=?",new String[]{selection2});
db.close();
break;
用execSQL实现
case R.id.update:
db = myDbHelper.getWritableDatabase();
String username1 = et_uname.getText().toString();
String password1 =et_upwd.getText().toString();
String selection2=et_selection.getText().toString();
db.execSQL("update az_user set userName=?,password=? where userName=?",new Object[]{username1,password1,selection2});
// ContentValues contentValues=new ContentValues();
// contentValues.put("userName",username1);
// contentValues.put("password",password1);
// db.update("az_user",contentValues,"userName=?",new String[]{selection2});
db.close();
break;
2. 总的实现代码
这里为了方便，条件查询、更新、删除都是通过用户名进行的，也是通过同一个框进行输入。
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:gravity="center"
>
<ImageView
android:layout_width="100dp"
android:layout_height="100dp"
android:background="@mipmap/ic_launcher"
></ImageView>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="用户名"
></TextView>
<EditText
android:id="@+id/uname"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="20sp"
android:hint="输入用户名">
</EditText>
<EditText
android:id="@+id/upwd"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入密码"
android:textSize="20sp"
></EditText>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="条件查询"
android:id="@+id/generate"></Button>
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="输入用户名"
android:textSize="20sp"
android:id="@+id/selection"></EditText>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="@+id/add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="5dp"
android:text="添加"></Button>
<Button
android:id="@+id/delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="5dp"
android:text="删除"></Button>
<Button
android:id="@+id/update"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="5dp"
android:text="修改"></Button>
<Button
android:id="@+id/select"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="5dp"
android:text="查询"></Button>
</LinearLayout>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="查询结果"
android:textSize="25sp"
android:id="@+id/showInfo"
></TextView>
</LinearLayout>
MainActivity.java
package com.example.myapp;
import androidx.annotation.ContentView;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.util.Map;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private Button generateBtn,addBtn,deleteBtn,updateBtn,selectBtn;
private EditText et_uname,et_upwd,et_selection;
private TextView showInfo;
private MyDbHelper myDbHelper;
private SQLiteDatabase db;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//初始化数据库
myDbHelper=new MyDbHelper(MainActivity.this,"MyDatabase.db",null,666);
initView();
//优化，给按钮设置监听器，但是太多按钮了
generateBtn.setOnClickListener(this);
addBtn.setOnClickListener(this);
deleteBtn.setOnClickListener(this);
updateBtn.setOnClickListener(this);
selectBtn.setOnClickListener(this);
}
private void initView() {
addBtn = findViewById(R.id.add);
generateBtn=findViewById(R.id.generate);
deleteBtn = findViewById(R.id.delete);
updateBtn = findViewById(R.id.update);
selectBtn = findViewById(R.id.select);
et_uname = findViewById(R.id.uname);
et_upwd = findViewById(R.id.upwd);
showInfo = findViewById(R.id.showInfo);
et_selection=findViewById(R.id.selection);
}
@Override
public void onClick(View v) {
switch (v.getId()){
//1.添加数据
case R.id.add:
//获取数据库对象
db = myDbHelper.getWritableDatabase();
String uname = et_uname.getText().toString();
String upwd = et_upwd.getText().toString();
//创建一个ContentValues对象用于存储记录的字段值;
// 以键值对存储，键对应字段名，值是字段的具体值
// ContentValues contentValues=new ContentValues();
//// contentValues.put("userId",1);//因为是自增长所以可以不用写
// contentValues.put("userName",uname);
// contentValues.put("password",upwd);
// db.insert("az_user",null,contentValues);
db.execSQL("insert into az_user(userName,password) values(?,?)", new Object[]{uname,upwd});
db.close();
break;
//2.查找全部记录
case R.id.select:
db = myDbHelper.getWritableDatabase();
//Cursor：结果集，结果集中会有游标指向结果集中的某一条记录。
Cursor cursor = db.query("az_user",new String[]{"userName","password"},null,null,null,null,null,null);
cursor.moveToFirst();
showInfo.setText("用户名："+cursor.getString(0)+",密码："+cursor.getString(1));
while(cursor.moveToNext()){
showInfo.append("\n"+"用户名："+cursor.getString(0)+",密码："+cursor.getString(1));
}
cursor.close();
db.close();
break;
case R.id.generate:
db=myDbHelper.getWritableDatabase();
String selection = et_selection.getText().toString();
// Cursor cursor1 = db.query("az_user",new String[]{"userName","password"},"userName=?",new String[] {selection},null,null,null,null);
Cursor cursor1=db.rawQuery("select userName,password from az_user where userName=?",new String[]{selection});
showInfo.setText("查询结果如下：");
while(cursor1.moveToNext()){
showInfo.append("\n"+"用户名："+cursor1.getString(0)+"密码："+cursor1.getString(1));
}
cursor1.close();
db.close();
//删除
case R.id.delete:
db = myDbHelper.getWritableDatabase();
String selection1 = et_selection.getText().toString();
// int i=db.delete("az_user","userName=?",new String[]{selection1});
db.execSQL("delete from az_user where userName=?",new Object[]{selection1});
// if(i>0){
// Toast.makeText(MainActivity.this,"删除成功,删除了"+i+"条",Toast.LENGTH_SHORT).show();
// }else{
// Toast.makeText(MainActivity.this,"删除失败",Toast.LENGTH_SHORT).show();
// }
db.close();
break;
//修改
case R.id.update:
db = myDbHelper.getWritableDatabase();
String username1 = et_uname.getText().toString();
String password1 =et_upwd.getText().toString();
String selection2=et_selection.getText().toString();
db.execSQL("update az_user set userName=?,password=? where userName=?",new Object[]{username1,password1,selection2});
// ContentValues contentValues=new ContentValues();
// contentValues.put("userName",username1);
// contentValues.put("password",password1);
// db.update("az_user",contentValues,"userName=?",new String[]{selection2});
db.close();
break;
}
}
//数据库帮助类
class MyDbHelper extends SQLiteOpenHelper {
//构造器作用：参数含义：上下文、数据库文件名称、结果集工厂、数据库版本号
public MyDbHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
//数据库初始化创建表或者视图文件
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table az_user(userId integer primary key autoincrement, userName varchar(20),password varchar(20))");
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
}
}
}
标签：userName,10,String,改查,APP,db,contentValues,new,null From： https://www.cnblogs.com/hmy22466/p/17225182.html