2021.3.6

在MainActivity里：

package com.example.myaccountapp;

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

import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ImageButton;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class MainActivity extends AppCompatActivity {

private DBHelper helper;
private ListView listView;
private ImageButton Add;
private List<costList>list;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initData();

}

private void initData() {
list=new ArrayList<>();
SQLiteDatabase db=helper.getReadableDatabase();
Cursor cursor=db.query("account",null,null,null,null,
null,null);
while (cursor.moveToNext()){
costList clist=new costList();//构造实例
clist.set_id(cursor.getString(cursor.getColumnIndex("_id")));
clist.setTitle(cursor.getString(cursor.getColumnIndex("Title")));
clist.setDate(cursor.getString(cursor.getColumnIndex("Date")));
clist.setMoney(cursor.getString(cursor.getColumnIndex("Money")));
list.add(clist);
}

listView.setAdapter(new ListAdapter(this,list));
db.close();
}

private void initView() {
helper=new DBHelper(MainActivity.this);
listView = findViewById(R.id.list_view);
Add=findViewById(R.id.add);
}

public void addAccount(View view){//跳转
Intent intent=new Intent(MainActivity.this,new_cost.class);
startActivityForResult(intent,1);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if(requestCode==1&&resultCode==1)
{
this.initData();
}
}
}