和谐共生（7）
这次学习了数据库的简单操作，可以添加数据，并返回在listView中
效果图
代码：
<?xml version=”1.0″ encoding=”utf-8″?>
<RelativeLayout 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”>
<ListView
android:id=”@+id/lv_user_list”
android:layout_width=”match_parent”
android:layout_height=”wrap_content”/>
<Button
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:id=”@+id/btn_add_info”
android:layout_alignParentBottom=”true”
android:text=”添加”/>
</RelativeLayout>
<?xml version=”1.0″ encoding=”utf-8″?>
<LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”
android:orientation=”vertical”
android:layout_width=”match_parent”
android:layout_height=”wrap_content”>
<TextView
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:gravity=”center”
android:padding=”5dp”
android:layout_marginBottom=”3dp”
android:text=”添加用户信息”
android:textSize=”23dp”/>
<EditText
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:id=”@+id/et_name”
android:hint=”请输入姓名”/>
<EditText
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:id=”@+id/et_desc”
android:hint=”请输入描述”/>
<LinearLayout
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:orientation=”horizontal”>
<Button
android:id=”@+id/btn_confirm”
android:layout_width=”0dp”
android:layout_height=”wrap_content”
android:layout_weight=”1″
android:text=”确定”/>
<Button
android:id=”@+id/btn_cancel”
android:layout_width=”0dp”
android:layout_height=”wrap_content”
android:layout_weight=”1″
android:text=”取消”/>
</LinearLayout>
</LinearLayout>
这个是弹出界面，用来填写用户的数据。
下面这个item用来设置信息显示的布局
<?xml version=”1.0″ encoding=”utf-8″?>
<LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”
android:layout_width=”match_parent”
android:padding=”3dp”
android:orientation=”vertical”
android:layout_height=”wrap_content”>
<TextView
android:text=”姓名”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:textSize=”20dp”
android:id=”@+id/tv_name”/>
<TextView
android:text=”描述”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:textSize=”18dp”
android:id=”@+id/tv_dec”/>
</LinearLayout>
后台代码
首先要有一个实体类（就不写了），平常写B/S使用的实体类
然后创建数据库和表
package com.example.dboperate;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
public class UserOpenHelper extends SQLiteOpenHelper {
public UserOpenHelper(@Nullable Context context) {
super(context, “user.db”, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
String sql=”create table user(_id integer primary key autoincrement,name varchar(20),dec varchar(50))”;
db.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
}
}
创建适配器，数据的显示
package com.example.dboperate;
import android.app.Application;
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
import java.util.List;
public class UserAdapter extends BaseAdapter {
private final Context context;
private final List<User> userList;
public UserAdapter(Context context, List<User> userList){
this.context=context;
this.userList=userList;
}
@Override
public int getCount() {
return userList.size();
}
@Override
public Object getItem(int i) {
return userList.get(i);
}
@Override
public long getItemId(int i) {
return userList.get(i).getId();
}
@Override
public View getView(int i, View view, ViewGroup viewGroup) {
if (view==null){
view=View.inflate(context,R.layout.item_user,null);
}
TextView tvName = view.findViewById(R.id.tv_name);
TextView tvDec = view.findViewById(R.id.tv_dec);
tvName.setText(userList.get(i).getName());
tvDec.setText(userList.get(i).getDec());
return view;
}
}
数据库操作
package com.example.dboperate;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class UserDao {
private final UserOpenHelper userOpenHelper;
private static UserDao userDao=null;
public UserDao(Context context) {
userOpenHelper = new UserOpenHelper(context);
}
public static UserDao getInstance(Context context){
if (userDao==null){
userDao=new UserDao(context);
}
return userDao;
}
//保存
public void insert(User user){
SQLiteDatabase db=userOpenHelper.getWritableDatabase();
ContentValues values=new ContentValues();
values.put(“name”,user.getName());
values.put(“dec”,user.getDec());
db.insert(“user”,null,values);
db.close();
}
//获取所有数据
public List<User> findAll(){
SQLiteDatabase db=userOpenHelper.getWritableDatabase();
Cursor cursor=db.query(“user”,new String[]{“_id”,”name”,”dec”},null,null,null,null,null);
List<User> userList=new ArrayList<>();
while (cursor.moveToNext()){
User user=new User();
user.setId(cursor.getInt(0));
user.setName(cursor.getString(1));
user.setDec(cursor.getString(2));
userList.add(user);
}
db.close();
return userList;
}
}
MainActivity
package com.example.dboperate;
import androidx.appcompat.app.AppCompatActivity;
import android.app.AlertDialog;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;
import java.util.List;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private ListView mUserList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//初始化控件
initUI();
//初始化数据
initData();
}
private void initData() {
UserDao userDao=UserDao.getInstance(getApplicationContext());
List<User> userList=userDao.findAll();
UserAdapter adapter = new UserAdapter(getApplicationContext(), userList);
mUserList.setAdapter(adapter);
}
private void initUI() {
mUserList=findViewById(R.id.lv_user_list);
findViewById(R.id.btn_add_info).setOnClickListener(this);
}
@Override
public void onClick(View view) {
if(view.getId()==R.id.btn_add_info){
showAlertDialog();
}
}
private void showAlertDialog() {
//实例化弹窗构造者对象
AlertDialog.Builder builder=new AlertDialog.Builder(this);
//自定义弹窗内容
AlertDialog alertDialog= builder.create();
View view = View.inflate(getApplicationContext(), R.layout.dialog_user_info, null);
alertDialog.setView(view);
alertDialog.show();
EditText etName=view.findViewById(R.id.et_name);
EditText etDec=view.findViewById(R.id.et_desc);
//点击事件
view.findViewById(R.id.btn_confirm).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String name=etName.getText().toString();
String dec=etDec.getText().toString();
if (name.length()==0||dec.length()==0){
Toast.makeText(getApplicationContext(),”内容不能为空”,Toast.LENGTH_SHORT).show();
return;
}
save2db(name,dec);
}
});
view.findViewById(R.id.btn_cancel).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
alertDialog.dismiss();
}
});
}
private void save2db(String name, String dec) {
UserDao userDao=UserDao.getInstance(getApplicationContext());
User user = new User(name, dec);
userDao.insert(user);
initData();//初始化数据
}
}
原创文章，作者：Maggie-Hunter，如若转载，请注明出处：https://blog.ytso.com/273152.html