package com.example.lenovo.myapplication;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class My extends SQLiteOpenHelper {
public My( Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table user(id integer primary key autoincrement,userid text,password text)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}

layout
<?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"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="活动一"
android:textSize="30sp"
android:layout_gravity="center"
android:textStyle="bold"
/>
<Button
android:id="@+id/b5"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="创建数据库"
android:textSize="25sp"
android:onClick="cj"
/>
<TextView
android:id="@+id/tv"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="数据库显示"
android:textSize="25sp"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
>
<TextView
android:layout_weight="1"
android:layout_width="0sp"
android:layout_height="wrap_content"
android:text="AA"
android:textSize="25sp"
/>
<TextView
android:layout_weight="1"
android:layout_width="0sp"
android:layout_height="wrap_content"
android:text="BB"
android:textSize="25sp"
android:gravity="center"/>
<TextView
android:layout_weight="1"
android:layout_width="0sp"
android:layout_height="match_parent"
android:text="BB"
android:textSize="25sp"
android:gravity="right"/>
</LinearLayout>
<EditText
android:id="@+id/et1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入账号："
android:textSize="25sp"/>
<EditText
android:id="@+id/et2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入密码："
android:textSize="25sp"/>
<Button
android:id="@+id/b1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="注册"
android:textSize="25sp"
android:gravity="center"
android:onClick="zc"/>
<Button
android:id="@+id/b2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="注销"
android:textSize="25sp"
android:gravity="center"
android:onClick="zx"/>
<Button
android:id="@+id/b3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="修改"
android:textSize="25sp"
android:gravity="center"
android:onClick="xg"/>
<Button
android:id="@+id/b4"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="查询"
android:textSize="25sp"
android:gravity="center"
android:onClick="cx"/>
</LinearLayout>

Main（1）
package com.example.lenovo.myapplication;
import android.content.ContentValues;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private My my;
private SQLiteDatabase db;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void cj(View view) {
my = new My(MainActivity.this,"aa.db",null,1);
db = my.getWritableDatabase();
TextView tv = findViewById(R.id.tv);
tv.setText(db.getPath());
}
public void zc(View view) {
EditText ET1 = findViewById(R.id.et1);
EditText ET2 = findViewById(R.id.et2);
String id = ET1.getText().toString();
String pwd = ET2.getText().toString();
ContentValues cv = new ContentValues();
cv.put("userid",id);
cv.put("password",pwd);
db.insert("user",null,cv);
Toast.makeText(this, "已添加账号：" + id + "密码："+ pwd, Toast.LENGTH_SHORT).show();
Intent intent = new Intent(MainActivity.this,Main3Activity.class);
startActivity(intent);
}
public void zx(View view) {
EditText ET1 = findViewById(R.id.et1);
String id = ET1.getText().toString();
db.delete("user","userid=?",new String[]{id});
Toast.makeText(this,"已删除账号： " + id,Toast.LENGTH_LONG).show();
}
public void xg(View view) {
EditText ET1 = findViewById(R.id.et1);
EditText ET2 = findViewById(R.id.et2);
String id = ET1.getText().toString();
String pwd = ET2.getText().toString();
ContentValues cv = new ContentValues();
cv.put("password",pwd);
db.update("user",cv,"userid=?",new String[]{id});
Toast.makeText(this,"已更新 " + id + " 新的密码为：" + pwd,Toast.LENGTH_LONG).show();
}
public void cx(View view) {
EditText ET1 = findViewById(R.id.et1);
EditText ET2 = findViewById(R.id.et2);
String id = ET1.getText().toString();
String pwd = ET2.getText().toString();
Cursor c = db.query("user",new String[]{"userid"},"userid=? and password=?",
new String[]{id,pwd},null,null,null);
if (c.moveToFirst()){
Toast.makeText(this, "登录成功！ ", Toast.LENGTH_SHORT).show();
Intent intent = new Intent(MainActivity.this,Main2Activity.class);
startActivity(intent);
}
else
Toast.makeText(this," 登录失败，请注册！ ",Toast.LENGTH_LONG).show();
}
}

Main（2）
package com.example.lenovo.myapplication;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
public class Main2Activity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
findViewById(R.id.b6).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(Main2Activity.this,MainActivity.class);
startActivity(intent);
}
});
}
}