项目地址

https://gitee.com/heziyan_code/note-book

项目结构

• Room数据库：AppDatabase/User/UserDao
• Main界面：将List中的内容显示出来
• Edit界面：编辑内容
  

Room数据库

关于Room的基本用法请看官网介绍：https://developer.android.google.cn/training/data-storage/room

定义id主键与content内容

@Entity
public class User {

    @PrimaryKey(autoGenerate = true)
    public int id;

    @ColumnInfo
    public String content;
}

创造增删改查方法

@Dao
public interface  UserDao {

    @Insert
    public void addContent(User user);

    @Query("SELECT * FROM user")
    public List<User> showThis();

    @Delete
    public void delete(User user);

    @Query("UPDATE user SET content = :content WHERE id = :id")
    public int updateUser(String content,int id);

    @Update
    public void updateUser(User... users);
}

创建主视图

创造布局界面

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/darker_gray"
    android:orientation="vertical" >
    <TextView
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:text="记事本列表"
        android:textSize="20sp"
        android:paddingTop="10dp"
        android:paddingBottom="5dp"
        android:background="#000"
        android:gravity="center"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" >

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/listview"
            android:background="#000"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>
    </LinearLayout>

    <Button
        android:id="@+id/btn_editnote"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/black"
        android:layout_gravity="center"
        android:text="添加备忘录"
        android:textSize="20sp" />

</LinearLayout>

显示效果

在Activity中为按钮和item添加事件与数据

public class MainActivity extends Activity {

    private Button btn_editnote;
    private RecyclerView mrmain;
    private AppDatabase db;
    private UserDao dao;
    private SharedPreferences spf;

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

        btn_editnote = findViewById(R.id.btn_editnote);
        btn_editnote.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this,EditView.class);
                Bundle bundle = new Bundle();
                bundle.putInt("num",-1);
                intent.putExtras(bundle);
                startActivity(intent);
            }
        });
        //数据库连接
        db = Room.databaseBuilder(this,AppDatabase.class,"test").allowMainThreadQueries().build();
        dao = db.userDao();
        List<User> users = dao.showThis();

//        spf = getSharedPreferences("data",MODE_PRIVATE);
//        String name = spf.getString("name", "");
//        int id_update = spf.getInt("id_update", 0);
//        System.out.println(id_update+":"+name);
//        User userabc = new User();
//        userabc.id = id_update;
//        userabc.content = name;
//        int i = dao.updateUser(name,id_update);
//        System.out.println("更新了"+i+"条数据");

        mrmain = findViewById(R.id.listview);
        mrmain.setLayoutManager(new LinearLayoutManager(MainActivity.this));
        mrmain.addItemDecoration(new MyDecortion());
        mrmain.setAdapter(new CustomAdapter(users, MainActivity.this, new CustomAdapter.OnItemClickListener() {
            @Override
            public void onClick(int pos,User user) {
                Intent intent = new Intent(MainActivity.this,EditView.class);
                Bundle bundle = new Bundle();
                bundle.putInt("id",pos);
                bundle.putString("content",users.get(pos).content);
                intent.putExtras(bundle);
                //修改时先删除该数据
                dao.delete(user);
                startActivity(intent);
            }

            @Override
            public void onLongClick(int pos, User user) {
                Toast.makeText(MainActivity.this,"这是第"+pos,Toast.LENGTH_SHORT).show();
                //对话框确认删除
                onCreateDialog(user).show();
            }
        }));
    }

    @Override
    protected void onResume() {
        super.onResume();
        onCreate(null);
    }

    public Dialog onCreateDialog(User user) {
        // Use the Builder class for convenient dialog construction
        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
        builder.setMessage("确认删除？")
                .setPositiveButton("确定", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        // FIRE ZE MISSILES!
                        dao.delete(user);
                        onCreate(null);//刷新界面
                    }
                })
                .setNegativeButton("取消", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        // User cancelled the dialog
                    }
                });
        // Create the AlertDialog object and return it
        return builder.create();
    }

    class MyDecortion extends RecyclerView.ItemDecoration{
        @Override
        public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
            super.getItemOffsets(outRect, view, parent, state);
            outRect.set(0,0,0,1);
        }
    }

}

与RecycleView相关的Adapter

Adapter详解https://www.cnblogs.com/java-six/p/15863312.html

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> {

    private List<User> users;
    private Context context;
    private OnItemClickListener listener;

    public CustomAdapter(List<User> users,Context context,OnItemClickListener listener) {
        this.users = users;
        this.context = context;
        this.listener = listener;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item,parent,false));
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Date date = new Date();
        SimpleDateFormat ft = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        holder.textView.setText(users.get(position).content);
        holder.tv_1.setText(ft.format(date));

        holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {
                listener.onLongClick(position,users.get(position));
                return false;
            }
        });
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                listener.onClick(position,users.get(position));
            }
        });
    }

    @Override
    public int getItemCount() {

        return users.size();
    }

    class ViewHolder extends RecyclerView.ViewHolder{

        private TextView textView,tv_1;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            textView = itemView.findViewById(R.id.tv_content);
            tv_1 = itemView.findViewById(R.id.tv_date);
        }
    }

    public interface OnItemClickListener{
        void onClick(int pos,User user);
        void onLongClick(int pos,User user);
    }
}

Edit界面

功能：点击按钮挑传到空白界面，点击item跳转到修改界面

编辑界面展示

<?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:background="@color/black"
    android:orientation="vertical" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <Button
            android:id="@+id/btn_cancel"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:background="@color/black"
            android:textColor="#fff"
            android:text="取消" />

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:background="@color/black"
            android:layout_gravity="center"
            android:layout_weight="1"
            android:orientation="vertical" >

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:textColor="#fff"
                android:text="编辑备忘录"
                android:textSize="20sp" />

            <TextView
                android:id="@+id/tv_date"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="" />
        </LinearLayout>

        <Button
            android:id="@+id/btn_ok"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:background="@color/black"
            android:textColor="#fff"
            android:text="保存" />
    </LinearLayout>

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="vertical" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginLeft="2dp"
            android:orientation="vertical" >

            <EditText
                android:id="@+id/et_content"
                android:textColor="#fff"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:background="@color/black"
                android:textSize="20sp" />
        </LinearLayout>
    </ScrollView>

</LinearLayout>

EditActivity逻辑跳转

public class EditView extends AppCompatActivity {

    public AppDatabase db;
    private EditText et_content;
    private Button btn_cancel,btn_ok;
    private Bundle bundle;
    private SharedPreferences spf;
    private SharedPreferences.Editor editor;
    private int i = 0;
    private User user = new User();
    private UserDao dao;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_edit_view);
        et_content = findViewById(R.id.et_content);
        btn_ok = findViewById(R.id.btn_ok);
        btn_cancel = findViewById(R.id.btn_cancel);
        db = Room.databaseBuilder(this,AppDatabase.class,"test").allowMainThreadQueries().build();
        dao = db.userDao();

        bundle = getIntent().getExtras();
        int num = bundle.getInt("num");
        int idnum = bundle.getInt("id");
        String content = bundle.getString("content");
        User user_yuanlai = new User();
        user_yuanlai.id = idnum;
        user_yuanlai.content = content;

        if(num<0) {
            i = 1;
            btn_ok.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    User user = new User();
                    Date dNow = new Date();
                    SimpleDateFormat ft = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
                    String s = et_content.getText().toString();
                    user.content = s;
//                user.date = ft.format(dNow);
                    dao.addContent(user);

                    Toast.makeText(getApplicationContext(), "保存成功", Toast.LENGTH_SHORT).show();
                    onBackPressed();

                }
            });

        }else{
            dao.delete(user_yuanlai);
            System.out.println(idnum+":"+content);
            et_content.setText(content);

            user.content = content;
            btn_ok.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {

                    int id = bundle.getInt("idnum");
                    String s = et_content.getText().toString();
                    spf = getSharedPreferences("data",MODE_PRIVATE);
                    editor = spf.edit();
                    user.content = s;
                    editor.putString("name",s);
                    editor.putInt("id_update",idnum);
                    editor.apply();
                    dao.updateUser(user);
                    //更新无效

                    dao.addContent(user);
                    i = 1;
                    Toast.makeText(getApplicationContext(), "修改成功", Toast.LENGTH_SHORT).show();
                    onBackPressed();
                }
            });


        }

        btn_cancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(EditView.this,MainActivity.class);
                startActivity(intent);
                onBackPressed();
            }
        });
    }

    @Override
    protected void onPause() {
        super.onPause();
        if(i==0)
        dao.addContent(user);
    }
}