一、首先创建保存数据的表

Notedatabase,java

package com.example.biji_1;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class NoteDatabase extends SQLiteOpenHelper {
    public static final String TABLE_NAME ="notes";
    public static final String CONTENT ="content";
    public static final String ID ="_id";
    public static final String TIME ="time";
    public static final String MODE ="mode";
    public  NoteDatabase(Context context){
        super(context,"notes",null,1);
    }
    @Override
    public void onCreate(SQLiteDatabase db){
        db.execSQL("CREATE TABLE " + TABLE_NAME + "(" + ID
                + " INTEGER PRIMARY KEY AUTOINCREMENT, "
                + CONTENT + " TEXT NOT NULL, "
                + TIME + " TEXT NOT NULL, "
                + MODE + " INTEGER DEFAULT 1)");
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion,int newVersion){
    }
}

二、主界面

MainAcitivity.java

public class MainActivity extends BaseActivity implements AdapterView.OnItemClickListener {
    //test gittt
    private NoteDatabase dbHelper;
    private Context context = this;
    final String TAG = "tag";
    FloatingActionButton btn;
    private ListView lv;
    private NoteAdapter adapter;
    private List<Note> noteList = new ArrayList<Note>();
    private Toolbar myToolbar;
    //弹出菜单
    private PopupWindow popupWindow;
    private PopupWindow popupCover;
    private ViewGroup customView;
    private ViewGroup coverView;
    private LayoutInflater layoutInflater;
    private RelativeLayout main;
    private WindowManager wm;
    private DisplayMetrics metrics;
    private TextView setting_text;
    private ImageView setting_image;

    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initPrefs();
        btn = (FloatingActionButton) findViewById(R.id.fab);
        lv = findViewById(R.id.lv);

        myToolbar = findViewById(R.id.myToolbar);
        adapter = new NoteAdapter(getApplicationContext(), noteList);
        refreshListView();
        lv.setAdapter(adapter);

        setSupportActionBar(myToolbar);
        getSupportActionBar().setHomeButtonEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true); //设置toolbar取代actionbar
        initPopUpView();
        myToolbar.setNavigationIcon(R.drawable.ic_baseline_menu_24);
        myToolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG, "onClick: shit");
                showPopUpView();
            }
        });

        lv.setOnItemClickListener(this);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, EditActivity.class);
                intent.putExtra("mode", 4);
                startActivityForResult(intent, 0);
            }
        });

    }
    public void initPopUpView(){
        layoutInflater = (LayoutInflater) MainActivity.this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        customView = (ViewGroup) layoutInflater.inflate(R.layout.setting_layout, null);
        coverView = (ViewGroup) layoutInflater.inflate(R.layout.setting_cover, null);
        main = findViewById(R.id.main_layout);
        wm = getWindowManager();
        metrics = new DisplayMetrics();
        wm.getDefaultDisplay().getMetrics(metrics);
    }
    public void showPopUpView(){
        int width = metrics.widthPixels;
        int height = metrics.heightPixels;

        popupCover = new PopupWindow(coverView, width, height, false);
        popupWindow = new PopupWindow(customView, (int) (width * 0.7), height, true);
        popupWindow.setBackgroundDrawable(new ColorDrawable(Color.WHITE));


        //在主界面加载成功之后 显示弹出
        findViewById(R.id.main_layout).post(new Runnable() {
            @Override
            public void run() {
                popupCover.showAtLocation(main, Gravity.NO_GRAVITY, 0, 0);
                popupWindow.showAtLocation(main, Gravity.NO_GRAVITY, 0, 0);

                setting_image = customView.findViewById(R.id.setting_settings_image);
                setting_text = customView.findViewById(R.id.setting_settings_text);

                setting_image.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        startActivity(new Intent(MainActivity.this, UserSettingsActivity.class));
                    }
                });

                setting_text.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        startActivity(new Intent(MainActivity.this, UserSettingsActivity.class));
                    }
                });

                coverView.setOnTouchListener(new View.OnTouchListener() {
                    @Override
                    public boolean onTouch(View v, MotionEvent event) {
                        popupWindow.dismiss();
                        return true;
                    }
                });

                popupWindow.setOnDismissListener(new PopupWindow.OnDismissListener() {
                    @Override
                    public void onDismiss() {
                        popupCover.dismiss();
                        Log.d(TAG, "onDismiss: test");
                    }
                });
            }

        });

    }
    public void initPrefs(){
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getBaseContext());
        SharedPreferences.Editor editor = sharedPreferences.edit();
        if (!sharedPreferences.contains("nightMode")) {
            editor.putBoolean("nightMode", false);
            editor.commit();
        }
    }
    // 接受startActivityForResult的结果
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data){

        int returnMode;
        long note_Id;
        returnMode = data.getExtras().getInt("mode", -1);
        note_Id = data.getExtras().getLong("id", 0);


        if (returnMode == 1) {  //update current note

            String content = data.getExtras().getString("content");
            String time = data.getExtras().getString("time");
            int tag = data.getExtras().getInt("tag", 1);

            Note newNote = new Note(content, time, tag);
            newNote.setId(note_Id);
            CRUD op = new CRUD(context);
            op.open();
            op.updateNote(newNote);
            op.close();
        } else if (returnMode == 0) {  // create new note
            String content = data.getExtras().getString("content");
            String time = data.getExtras().getString("time");
            int tag = data.getExtras().getInt("tag", 1);

            Note newNote = new Note(content, time, tag);
            CRUD op = new CRUD(context);
            op.open();
            op.addNote(newNote);
            op.close();
        } else if (returnMode == 2) { // delete
            Note curNote = new Note();
            curNote.setId(note_Id);
            CRUD op = new CRUD(context);
            op.open();
            op.removeNote(curNote);
            op.close();
        }
        else{

        }
        refreshListView();
        super.onActivityResult(requestCode, resultCode, data);

    }  //判断笔记状态
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);

        //search setting
        MenuItem mSearch = menu.findItem(R.id.action_search);
        SearchView mSearchView = (SearchView) mSearch.getActionView();

        mSearchView.setQueryHint("请输入搜索内容");
        mSearchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
            @Override
            public boolean onQueryTextSubmit(String query) {
                return false;
            }

            @Override
            public boolean onQueryTextChange(String newText) {
                adapter.getFilter().filter(newText);
                return false;
            }
        });

        return super.onCreateOptionsMenu(menu);
    }   //搜索
    @Override
    public boolean onOptionsItemSelected(MenuItem item){
        switch (item.getItemId()){
            case R.id.menu_clear:
                new AlertDialog.Builder(MainActivity.this)
                        .setMessage("删除全部吗？")
                        .setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                dbHelper = new NoteDatabase(context);
                                SQLiteDatabase db = dbHelper.getWritableDatabase();
                                db.delete("notes", null, null);
                                db.execSQL("update sqlite_sequence set seq=0 where name='notes'");
                                refreshListView();
                            }
                        }).setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                }).create().show();
                break;

        }
        return super.onOptionsItemSelected(item);
    }  //主界面删除
    public void refreshListView(){

        CRUD op = new CRUD(context);
        op.open();
        // set adapter
        if (noteList.size() > 0) noteList.clear();
        noteList.addAll(op.getAllNotes());
        op.close();
        adapter.notifyDataSetChanged();
    }  //刷新list
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        switch (parent.getId()) {
            case R.id.lv:
                Note curNote = (Note) parent.getItemAtPosition(position);
                Intent intent = new Intent(MainActivity.this, EditActivity.class);
                intent.putExtra("content", curNote.getContent());
                intent.putExtra("id", curNote.getId());
                intent.putExtra("time", curNote.getTime());
                intent.putExtra("mode", 3);     // MODE of 'click to edit'
                intent.putExtra("tag", curNote.getTag());
                startActivityForResult(intent, 1);      //collect data from edit
                Log.d(TAG, "onItemClick: " + position);
                break;
        }
    } //携带数据
}

2.1 activity_main.xml

三、:EditActivity.java

package com.example.biji_1;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.widget.Toolbar;

import java.text.SimpleDateFormat;
import java.util.Date;
public class EditActivity extends BaseActivity {
    EditText et;
    private Toolbar myToolbar;
    private String old_content = "";
    private String old_time = "";
    private int old_Tag = 1;
    private long id = 0;
    private int openMode = 0;
    private int tag = 1;
    public Intent intent = new Intent(); // message to be sent
    private boolean tagChange = false;
    private final String TAG = "tag";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.edit_layout);

        myToolbar = findViewById(R.id.myToolbar);
        setSupportActionBar(myToolbar);
        getSupportActionBar().setHomeButtonEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true); //设置toolbar取代actionbar

        myToolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                autoSetMessage();
                setResult(RESULT_OK, intent);
                finish();

            }
        });



        myToolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                autoSetMessage();
                setResult(RESULT_OK, intent);
                finish();
            }
        });
        et = findViewById(R.id.et_1);
        Intent getIntent = getIntent();
        openMode = getIntent.getIntExtra("mode", 0);

        if (openMode == 3) {//打开已存在的note
            id = getIntent.getLongExtra("id", 0);
            old_content = getIntent.getStringExtra("content");
            old_time = getIntent.getStringExtra("time");
            old_Tag = getIntent.getIntExtra("tag", 1);
            et.setText(old_content);
            et.setSelection(old_content.length());
            Log.d("TAG","打开");

        }
    }
    //渲染菜单栏
    @Override
    public boolean onCreateOptionsMenu(Menu menu_1) {
        getMenuInflater().inflate(R.menu.edit_menu,menu_1);
        return super.onCreateOptionsMenu(menu_1);
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item){
        switch (item.getItemId()){
            case R.id.delete:
                new AlertDialog.Builder(EditActivity.this)
                        .setMessage("删除吗？")
                        .setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                if (openMode == 4){ // new note
                                    intent.putExtra("mode", -1);
                                    setResult(RESULT_OK, intent);
                                }
                                else { // existing note
                                    intent.putExtra("mode", 2);
                                    intent.putExtra("id", id);
                                    setResult(RESULT_OK, intent);
                                }
                                finish();
                            }
                        }).setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                }).create().show();
                break;
        }
        return super.onOptionsItemSelected(item);
    }
    public boolean onKeyDown(int keyCode, KeyEvent event){
        if (keyCode == KeyEvent.KEYCODE_HOME){
            return true;
        }
        else if (keyCode == KeyEvent.KEYCODE_BACK){
            autoSetMessage();
            setResult(RESULT_OK, intent);
            finish();
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }
    public void autoSetMessage(){
        if(openMode == 4){
            if(et.getText().toString().length() == 0){
                intent.putExtra("mode", -1); //nothing new happens.
            }
            else{
                intent.putExtra("mode", 0); // new one note;
                intent.putExtra("content", et.getText().toString());
                intent.putExtra("time", dateToStr());
                intent.putExtra("tag", tag);
            }
        }
        else {
            if (et.getText().toString().equals(old_content) && !tagChange)
                intent.putExtra("mode", -1); // edit nothing
            else {
                intent.putExtra("mode", 1); //edit the content
                intent.putExtra("content", et.getText().toString());
                intent.putExtra("time", dateToStr());
                intent.putExtra("id", id);
                intent.putExtra("tag", tag);
            }
        }
    }
    public String dateToStr(){
        Date date = new Date();
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        return simpleDateFormat.format(date);
    }
}

3.1 edit_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <androidx.appcompat.widget.Toolbar
        android:id="@+id/myToolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:elevation="4dp"
        app:titleTextColor="#FFEBCD"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
        />
    <EditText
        android:id="@+id/et_1"
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:gravity="top"
        />

</LinearLayout>

四、对笔记进行增删查改

CRUD.java

package com.example.biji_1;

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

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

public class CRUD {
    SQLiteOpenHelper dbHandler;
    SQLiteDatabase db;

    private static final String[] columns = {
            NoteDatabase.ID,
            NoteDatabase.CONTENT,
            NoteDatabase.TIME,
            NoteDatabase.MODE
    };

    public CRUD(Context context){
        dbHandler = new NoteDatabase(context);
    }

    public void open(){
        db = dbHandler.getWritableDatabase();
    }

    public void close(){
        dbHandler.close();
    }

    //把note 加入到database里面
    public Note addNote(Note note){
        //add a note object to database
        ContentValues contentValues = new ContentValues();
        contentValues.put(NoteDatabase.CONTENT, note.getContent());
        contentValues.put(NoteDatabase.TIME, note.getTime());
        contentValues.put(NoteDatabase.MODE, note.getTag());
        long insertId = db.insert(NoteDatabase.TABLE_NAME, null, contentValues);
        note.setId(insertId);
        return note;
    }

    public Note getNote(long id){
        //get a note from database using cursor index
        Cursor cursor = db.query(NoteDatabase.TABLE_NAME,columns,NoteDatabase.ID + "=?",
                new String[]{String.valueOf(id)},null,null, null, null);
        if (cursor != null) cursor.moveToFirst();
        Note e = new Note(cursor.getString(1),cursor.getString(2), cursor.getInt(3));
        return e;
    }

    @SuppressLint("Range")
    public List<Note> getAllNotes(){
        Cursor cursor = db.query(NoteDatabase.TABLE_NAME,columns,null,null,null, null, null);

        List<Note> notes = new ArrayList<>();
        if(cursor.getCount() > 0){
            while(cursor.moveToNext()){
                Note note = new Note();
                note.setId(cursor.getLong(cursor.getColumnIndex(NoteDatabase.ID)));
                note.setContent(cursor.getString(cursor.getColumnIndex(NoteDatabase.CONTENT)));
                note.setTime(cursor.getString(cursor.getColumnIndex(NoteDatabase.TIME)));
                note.setTag(cursor.getInt(cursor.getColumnIndex(NoteDatabase.MODE)));
                notes.add(note);
            }
        }
        return notes;
    } //查找笔记

    public int updateNote(Note note) {
        //update the info of an existing note
        ContentValues values = new ContentValues();
        values.put(NoteDatabase.CONTENT, note.getContent());
        values.put(NoteDatabase.TIME, note.getTime());
        values.put(NoteDatabase.MODE, note.getTag());
        // updating row
        return db.update(NoteDatabase.TABLE_NAME, values,
                NoteDatabase.ID + "=?",new String[] { String.valueOf(note.getId())});
    } //更新笔记

    public void removeNote(Note note) {
        //remove a note according to ID value
        db.delete(NoteDatabase.TABLE_NAME, NoteDatabase.ID + "=" + note.getId(), null);
    }  //删除笔记
}

4.1 note_layout.xml

<?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:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="5dp"
    android:paddingBottom="12dp"
    android:orientation="vertical"
    android:background="@drawable/note_shape">


    <TextView
        android:id="@+id/tv_content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Content"
        android:textSize="20dp"
        android:textColor="	#00F5FF"
        android:singleLine="true"
        />

    <TextView
        android:id="@+id/tv_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Time"
        android:textSize="16dp"
        android:textColor="	#00F5FF"/>


</LinearLayout>