主要用了一些sql语句和学习了基本的增删改查的语句，完成了数据库的链接。
代码如下：
mainactivity代码：
package com.example.sqlite;
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;
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;//全局变量
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();
addBtn.setOnClickListener(this);
selectBtn.setOnClickListener(this);
generateBtn.setOnClickListener(this);
deleteBtn.setOnClickListener(this);
updateBtn.setOnClickListener(this);
}
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);
et_selection = findViewById(R.id.selection);
showInfo = findViewById(R.id.showInfo);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.add:
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，以键值对的方式存储，“键“对应就是字段名，”值"对应的就是某个字段的具体的值
// 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});
//?占位符
db.close();
break;
case R.id.select:
showInfo.setText(" ");
db = myDbHelper.getWritableDatabase();
//Cursor:结果集，结果集中会有游标，游标会指向结果集中的某一条记录，我们获取的记录是哪一条，初始时指向第一条记录
Cursor cursor = db.query("user", new String[]{"username", "password"}, null, null, null, null, null, null);
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("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.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();
//创建一个ContentValues对象，用于存储记录的字段值，以键值对的方式存储，“键“对应就是字段名，”值"对应的就是某个字段的具体的值
ContentValues contentValues=new ContentValues();
contentValues.put("username",username1);
contentValues.put("password",password1);
db.update("user",contentValues,"username=?",new String[]{selection2});
db.close();
break;
}
}
//快速格式化的快捷键ctrl+alt+l
//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，版本号
public MyDbHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
//数据库初始化的时候，用于创建表或者视图文件
@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 sqLiteDatabase, int i, int i1) {
}
}
}
布局代码如下：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
android:orientation="vertical">
<ImageView
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_gravity="center"
android:src="@mipmap/ic_launcher"
></ImageView>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="用户名："
android:textColor="@color/black"></TextView>
<EditText
android:id="@+id/username"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="请输入用户名"
android:textColorHint="@color/black"></EditText>
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="密码："
android:textColor="@color/black"></TextView>
<EditText
android:id="@+id/password"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="请输入密码"
android:password="true"
android:textColorHint="@color/black"></EditText>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<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="wrap_content"
android:layout_height="wrap_content"
android:hint="请输入查询用户名:"
android:layout_gravity="center"
android:id="@+id/selection"></EditText>
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/add"
android:onClick="dengluclick"
android:text="添加"
></Button>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/delete"
android:onClick="zhuceclick"
android:text="删除"
></Button>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="zhuceclick"
android:id="@+id/update"
android:text="修改"
></Button>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="zhuceclick"
android:id="@+id/select"
android:text="查询"
></Button>
</LinearLayout>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="显示查询结果"
android:gravity="center"
android:layout_gravity="center"
android:id="@+id/showInfo"
android:textColor="@color/black"></TextView>
</LinearLayout>
