安卓开发学习02 | 易学教程

经过了一上午的折腾，大致了解了如何开发一个疫情每日登录APP，首先我们需要使用数据库存储数据，Android Studio自带了SQLite作为数据库，可以通过DataBaseHelper来实现，但毕竟还是有些繁琐。今天主要学习了Google的数据库框架Room框架，Room框架由三部分组成，Entity(实体)、Dao（操作接口层）、DataBase(继承了RoomDatabase的自定义类），下面是一个小demo:

首先是Entity

package com.michael.roomdemo.database;

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.Ignore;
import androidx.room.PrimaryKey;

/**
 * Model
 * */
@Entity(tableName = "student")
public class Student
{
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "id", typeAffinity = ColumnInfo.INTEGER)
    public int id;

    @ColumnInfo(name = "name", typeAffinity = ColumnInfo.TEXT)
    public String name;

    @ColumnInfo(name = "age", typeAffinity = ColumnInfo.TEXT)
    public String age;

    /**
     * Room会使用这个构造器来存储数据，也就是当你从表中得到Student对象时候，Room会使用这个构造器
     * */
    public Student(int id, String name, String age)
    {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    /**
     * 由于Room只能识别和使用一个构造器，如果希望定义多个构造器，你可以使用Ignore标签，让Room忽略这个构造器
     * 同样，@Ignore标签还可用于字段，使用@Ignore标签标记过的字段，Room不会持久化该字段的数据
     * */
    @Ignore
    public Student(String name, String age)
    {
        this.name = name;
        this.age = age;
    }
}

这里需要使用@Entity来注解该类
至少要有一个主键@PrimaryKey

然后是Dao层：

package com.michael.roomdemo.database;

import java.util.List;

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

/**
 * DAO
 *
 * 对数据库表的增删改查
 *
 * */
@Dao
public interface StudentDao
{
    @Insert
    void insertStudent(Student student);

    @Delete
    void deleteStudent(Student student);

    @Update
    void updateStudent(Student student);

    @Query("SELECT * FROM student")
    List<Student> getStudentList();

    @Query("SELECT * FROM student WHERE id = :id")
    Student getStudentById(int id);
}

使用@Dao注解该接口
@Insert, @Update, @Delete,@Query代表我们常用的插入、更新、删除、查询数据库操作
@Insert, @Update, @Delete可以传入多种不同的参数。
@Query也可以返回多种不同的类型。

然后是我们的自定义数据库：

package com.michael.roomdemo.database;

import android.content.Context;


import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;

@Database(entities = {Student.class}, version = 1,exportSchema = false)
public abstract class MyDatabase extends RoomDatabase
{
    private static final String DATABASE_NAME = "my_db";

    private static MyDatabase databaseInstance;

    public static synchronized MyDatabase getInstance(Context context)
    {
        if(databaseInstance == null)
        {
            databaseInstance = Room
                    .databaseBuilder(context.getApplicationContext(), MyDatabase.class, DATABASE_NAME)
                    .build();
        }
        return databaseInstance;
    }

    public abstract StudentDao studentDao();
}

在定义好这些基本操作后，我们来看看界面：

界面比较简陋，主要是点击添加student后就弹出添加的activity

然后长按列表元素后会触发事件，有更新和删除选项，依次弹出相应的activity

前台代码就不放了，主要放一下后台：

package com.michael.roomdemo;

import android.content.DialogInterface;
import android.os.AsyncTask;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.AdapterView;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import com.michael.roomdemo.database.MyDatabase;
import com.michael.roomdemo.database.Student;

import java.util.ArrayList;
import java.util.List;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity
{

    private MyDatabase myDatabase;
    private List<Student> studentList;
    private StudentAdapter studentAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViewById(R.id.btnInsertStudent).setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                openAddStudentDialog();
            }
        });

        ListView lvStudent = findViewById(R.id.lvStudent);
        studentList = new ArrayList<>();
        studentAdapter = new StudentAdapter(MainActivity.this, studentList);
        lvStudent.setAdapter(studentAdapter);
        lvStudent.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener()
        {
            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id)
            {
                updateOrDeleteDialog(studentList.get(position));
                return false;
            }
        });

        myDatabase = MyDatabase.getInstance(this);

        new QueryStudentTask().execute();
    }
    //弹出选择是删除还是更新的选择框
    private void updateOrDeleteDialog(final Student student)
    {
        final String[] options = new String[]{"更新", "删除"};
        new AlertDialog.Builder(MainActivity.this)
                .setTitle("")
                .setItems(options, new DialogInterface.OnClickListener()
                        {
                            @Override
                            public void onClick(DialogInterface dialog, int which)
                            {
                                if(which == 0)
                                {
                                    openUpdateStudentDialog(student);
                                }
                                else if(which == 1)
                                {
                                    new DeleteStudentTask(student).execute();
                                }
                            }
                        }).show();
    }
    //弹出添加学生的Dialog
    private void openAddStudentDialog()
    {
        View customView = this.getLayoutInflater().inflate(R.layout.dialog_layout_student, null);
        final EditText etName = customView.findViewById(R.id.etName);
        final EditText etAge = customView.findViewById(R.id.etAge);

        final AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
        AlertDialog dialog = builder.create();
        dialog.setTitle("Add Student");
        dialog.setButton(DialogInterface.BUTTON_POSITIVE, "OK", new DialogInterface.OnClickListener()
        {

            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                if (TextUtils.isEmpty(etName.getText().toString()) || TextUtils.isEmpty(etAge.getText().toString()))
                {
                    Toast.makeText(MainActivity.this, "输入不能为空", Toast.LENGTH_SHORT).show();
                } else
                {
                    new InsertStudentTask(etName.getText().toString(), etAge.getText().toString()).execute();
                }
            }
        });
        dialog.setButton(DialogInterface.BUTTON_NEGATIVE, "CANCEL", new DialogInterface.OnClickListener()
        {
            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                dialog.dismiss();
            }
        });
        dialog.setView(customView);
        dialog.show();
    }
    //弹出更改学生信息的dialog
    private void openUpdateStudentDialog(final Student student)
    {
        if (student == null)
        {
            return;
        }
        View customView = this.getLayoutInflater().inflate(R.layout.dialog_layout_student, null);
        final EditText etName = customView.findViewById(R.id.etName);
        final EditText etAge = customView.findViewById(R.id.etAge);
        etName.setText(student.name);
        etAge.setText(student.age);

        final AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
        AlertDialog dialog = builder.create();
        dialog.setTitle("Update Student");
        dialog.setButton(DialogInterface.BUTTON_POSITIVE, "OK", new DialogInterface.OnClickListener()
        {

            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                if (TextUtils.isEmpty(etName.getText().toString()) || TextUtils.isEmpty(etAge.getText().toString()))
                {
                    Toast.makeText(MainActivity.this, "输入不能为空", Toast.LENGTH_SHORT).show();
                } else
                {
                    new UpdateStudentTask(student.id, etName.getText().toString(), etAge.getText().toString()).execute();
                }
            }
        });
        dialog.setButton(DialogInterface.BUTTON_NEGATIVE, "CANCEL", new DialogInterface.OnClickListener()
        {
            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                dialog.dismiss();
            }
        });
        dialog.setView(customView);
        dialog.show();
    }
    //插入的异步操作
    private class InsertStudentTask extends AsyncTask<Void, Void, Void>
    {
        String name;
        String age;

        public InsertStudentTask(final String name, final String age)
        {
            this.name = name;
            this.age = age;
        }

        @Override
        protected Void doInBackground(Void... arg0)
        {
            myDatabase.studentDao().insertStudent(new Student(name, age));
            studentList.clear();
            studentList.addAll(myDatabase.studentDao().getStudentList());
            return null;
        }

        @Override
        protected void onPostExecute(Void result)
        {
            super.onPostExecute(result);
            studentAdapter.notifyDataSetChanged();
        }
    }
    //更新的异步操作
    private class UpdateStudentTask extends AsyncTask<Void, Void, Void>
    {
        int id;
        String name;
        String age;
        public UpdateStudentTask(final int id, final String name, final String age)
        {
            this.id = id;
            this.name = name;
            this.age = age;
        }

        @Override
        protected Void doInBackground(Void... arg0)
        {
            myDatabase.studentDao().updateStudent(new Student(id, name, age));
            studentList.clear();
            studentList.addAll(myDatabase.studentDao().getStudentList());
            return null;
        }

        @Override
        protected void onPostExecute(Void result)
        {
            super.onPostExecute(result);
            studentAdapter.notifyDataSetChanged();
        }
    }
    //删除的异步操作
    private class DeleteStudentTask extends AsyncTask<Void, Void, Void>
    {
        Student student;

        public DeleteStudentTask(Student student)
        {
            this.student = student;
        }

        @Override
        protected Void doInBackground(Void... arg0)
        {
            myDatabase.studentDao().deleteStudent(student);
            studentList.clear();
            studentList.addAll(myDatabase.studentDao().getStudentList());
            return null;
        }

        @Override
        protected void onPostExecute(Void result)
        {
            super.onPostExecute(result);
            studentAdapter.notifyDataSetChanged();
        }
    }
    //异步显示全部学生信息
    private class QueryStudentTask extends AsyncTask<Void, Void, Void>
    {
        public QueryStudentTask()
        {

        }

        @Override
        protected Void doInBackground(Void... arg0)
        {
            studentList.clear();
            studentList.addAll(myDatabase.studentDao().getStudentList());
            return null;
        }

        @Override
        protected void onPostExecute(Void result)
        {
            super.onPostExecute(result);
            studentAdapter.notifyDataSetChanged();
        }
    }
}

这是主要后台，可以看注释

适应器代码：

package com.michael.roomdemo;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import com.michael.roomdemo.database.Student;

import java.util.List;

public class StudentAdapter extends BaseAdapter
{

    private List<Student> data;
    private LayoutInflater layoutInflater;

    public StudentAdapter(Context context, List<Student> data)
    {
        this.data = data;
        layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    class ViewHolder
    {
        TextView tvId;
        TextView tvName;
        TextView tvAge;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent)
    {
        ViewHolder viewHolder;
        if (convertView == null)
        {
            convertView = layoutInflater.inflate(R.layout.list_item_student, null);
            viewHolder = new ViewHolder();
            viewHolder.tvId = convertView.findViewById(R.id.tvId);
            viewHolder.tvName = convertView.findViewById(R.id.tvName);
            viewHolder.tvAge = convertView.findViewById(R.id.tvAge);
            convertView.setTag(viewHolder);
        } else
        {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        viewHolder.tvId.setText(String.valueOf(data.get(position).id));
        viewHolder.tvName.setText(data.get(position).name);
        viewHolder.tvAge.setText(data.get(position).age);
        return convertView;
    }

    @Override
    public int getCount()
    {

        if (data == null)
        {
            return 0;
        }

        return data.size();
    }

    @Override
    public Student getItem(int position)
    {
        return data.get(position);
    }

    @Override
    public long getItemId(int position)
    {
        return position;
    }
}

来源：https://www.cnblogs.com/wushenjiang/p/12296343.html

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