进度3_家庭记账本App_Fragment使用SQLite实现简单存储及查询

AddFragment.java:

package com.example.familybooks;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.Toast;

public class AddFragment extends Fragment {
    @Nullable
    String TAG="TAG";
    private EditText costTitle,costMoney;
    private Button btn_go,btn_return;
    private DatePicker costDate;
    private SQLiteDatabase database;
    DatabaseHelper helper;

    @Override
    public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState){
        View view=inflater.inflate(R.layout.activity_add,container,false);
        return view;
    }

   public void onActivityCreate(Bundle savedInstanceState){
        super.onActivityCreated(savedInstanceState);

        costTitle=(EditText)getActivity().findViewById(R.id.et_costtitle);
        costMoney=(EditText)getActivity().findViewById(R.id.et_costmoney);
        costDate=(DatePicker) getActivity().findViewById(R.id.dp_costdate);

        helper=new DatabaseHelper(getActivity(),"account_cost",null,1);

        btn_go=(Button)getActivity().findViewById(R.id.btn_go);
        btn_go.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(getActivity(),"accoun_cost",Toast.LENGTH_LONG).show();
                database=helper.getWritableDatabase();
                Insert();

                costTitle.setText("");
                //costDate.setText("");
                costMoney.setText("");
                Toast.makeText(getActivity(),"accoun_cost",Toast.LENGTH_LONG).show();
            }
        });

        btn_return=(Button)getActivity().findViewById(R.id.btn_return);
        btn_return.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                //得到数据库
                database=helper.getWritableDatabase();
                //查询数据
                Query();

                Toast.makeText(getActivity(),"accoun_cost",Toast.LENGTH_LONG).show();
            }
        });

   }
   public void Query(){
       Cursor cursor=database.query("account_cost",null,null,null,null,null,null);
       if(cursor.moveToFirst()){
           do{
               String title=cursor.getString(cursor.getColumnIndex("title"));
               String date=cursor.getString(cursor.getColumnIndex("date"));
               String money=cursor.getString(cursor.getColumnIndex("money"));
               Log.i(TAG,"title:"+title);
               Log.i(TAG,"date:"+date);
               Log.i(TAG,"money:"+money);
           }while(cursor.moveToNext());
       }
       cursor.close();
    }

    public void Insert(){
        ContentValues values=new ContentValues();
        values.put("title",costTitle.getText().toString());
        values.put("date",costTitle.getText().toString());
        values.put("money",costMoney.getText().toString());
        database.insert("account_cost",null,values);
    }
}

DatabaseHelper.java:

package com.example.familybooks;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import androidx.annotation.Nullable;

public class DatabaseHelper extends SQLiteOpenHelper {

    private Context context;
    public DatabaseHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context,"account_daily",null, 1);
        this.context=context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table diary(id integer PRIMARY KEY AUTOINCREMENT,"

                +"costTitle text,costDate text,costMoney text)");

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        db.execSQL("drop table if exists diary");
        onCreate(db);
    }
}

总结：

SQLiteOpenHelper是个抽象类，在该类中有如下两个抽象方法，SQLiteOpenHelper的子类必须实现这两个方法。
      public abstract void onCreate(SQLiteDatabase db);
      public abstract void onUpdate(SQLiteDatabase db,int oldVersion,int newVersion);

如果数据库文件不存在，只有oncreate()被调用（该方法在创建数据库时被调用一次）。

如果数据库文件存在，会调用onupdate()方法升级数据库，并更新版本号。