android studio去除无用资源 android studio清除数据

本篇博客来介绍安卓studio的数据删除与修改

源码如下：

Mainactivity

package com.example.sqlitetest;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
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;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private Button generateBtn,addBtn,deleteBtn,updateBtn,selectBtn;
    private EditText et_username,et_password,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);
        myDbhelper=new MyDbHelper(MainActivity.this,"MyDatabase.db",null,666);
        initView();
        generateBtn.setOnClickListener(this);
        addBtn.setOnClickListener(this);
        selectBtn.setOnClickListener(this);
        deleteBtn.setOnClickListener(this);
        updateBtn.setOnClickListener(this);
    }

    @SuppressLint("WrongViewCast")
    private void initView() {
       generateBtn=findViewById(R.id.generate);
        addBtn=findViewById(R.id.add);
        deleteBtn=findViewById(R.id.delete);
        updateBtn=findViewById(R.id.update);
        selectBtn=findViewById(R.id.select);
        et_username=findViewById(R.id.username);
         et_password=findViewById(R.id.password);
       showInfo=findViewById(R.id.showInfo);
        et_selection=findViewById(R.id.selection);
    }

    @Override
    public void onClick(View v) {
        switch(v.getId())
        {

            case R.id.add:
                //通过帮助类获取数据对象
                db=myDbhelper.getWritableDatabase();
                String username=et_username.getText().toString();
                String password=et_password.getText().toString();

               /* //创建一个ContentValues对象，用于存储记录的字段值，以键值对的方式储存，“键”对应就是字段名，“值”对应就是某个字段具体的值
                ContentValues contentValues=new ContentValues();

                contentValues.put("userName",username);
                contentValues.put("password",password);
                db.insert("user",null,contentValues);*/
                db.execSQL("insert into user(userName,password) values(?,?)",new Object[]{username,password});
             db.close();
                break;
            case R.id.select://普通查询
                db=myDbhelper.getWritableDatabase();
                Cursor cursor=db.query("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://条件查询
                db=myDbhelper.getWritableDatabase();
                String selection=et_selection.getText().toString();
               // Cursor cursor1=db.query("user",new String[]{"username","password"},"username=?",new String[]{selection},null,null,null,null);
                Cursor cursor1=db.rawQuery("select userName,password from 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();
                break;
            case R.id.delete:
                db=myDbhelper.getWritableDatabase();
                String selection1=et_selection.getText().toString();
                /*int i=db.delete("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.execSQL("delete from user where username=?",new Object[]{selection1});

                db.close();
                break;
                case R.id.update:
                    db=myDbhelper.getWritableDatabase();
                    String username1=et_username.getText().toString();
                    String password1=et_password.getText().toString();
                    String selection2=et_selection.getText().toString();
                    db.execSQL("update 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("user",contentValues,"userName=?",new String[]{selection2});

                     */
                    db.close();
                   break;

        }
    }

    //格式化快捷键 ctrl+alt+l
    //数据库帮助类
    class MyDbHelper extends SQLiteOpenHelper{
//构造器的作用，参数含义：上下文，数据库名称，结果集工厂，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，用来建表
        @Override
        public void onCreate(SQLiteDatabase db) {
db.execSQL("create table user(user_id integer primary key autoincrement,userName varchar(10),password varchar(10))");
        }
//升级方法
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        }
    }
}

在源码里面包含了安卓studio内数据的增删改查内容，通过

setOnClickListener(this)和

 public void onClick(View v) {

switch(v.getId())
}
语句实现了通过调用switch语句进行增删改查，每种方法都要两种形式