怎么用java写安卓 用java写安卓app

本文基于Java实现了一个简单的记事本安卓app，用的是SQLite数据库，包括布局文件、源码及实现图。

布局设计

记事本主界面

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http:///apk/res/android"
    xmlns:app="http:///apk/res-auto"
    xmlns:tools="http:///tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".NoteActivity">
    
    <ListView
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginTop="8dp"
        android:layout_below="@+id/myToolbar"
        android:divider="?attr/lvBackground"
        android:dividerHeight="8dp"
        >

    </ListView>

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/myToolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        android:elevation="4dp"
        app:titleTextColor="?attr/titleColor"
        android:theme="?attr/toolbarTheme"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light">
    </androidx.appcompat.widget.Toolbar>

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:layout_marginEnd="36dp"
        android:layout_marginBottom="48dp"
        android:clickable="true"
        android:focusable="true"
        android:src="@drawable/ic_add_white_24dp"
        />
    
</RelativeLayout>

        对记事本编辑的页面

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http:///apk/res/android"
    xmlns:app="http:///apk/res-auto"
    xmlns:tools="http:///tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".EditNoteActivity">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/my_Toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        android:elevation="4dp"
        app:titleTextColor="?attr/titleColor"
        android:theme="?attr/toolbarTheme"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light">
    </androidx.appcompat.widget.Toolbar>

    <EditText
        android:id="@+id/et"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:inputType="text"
        android:gravity="top">
    </EditText>


</LinearLayout>

代码

        Note实体类

                记事信息实体类

public class Note {
    private long id;
    private String content;
    private String time;
    private int tag;

    public Note() {
    }

    public Note(String content, String time, int tag) {
        this.content = content;
        this.time = time;
        this.tag = tag;
    }

    public long getId() {
        return id;
    }

    public String getContent() {
        return content;
    }

    public String getTime() {
        return time;
    }

    public int getTag() {
        return tag;
    }

    public void setId(long id) {
        this.id = id;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public void setTime(String time) {
        this.time = time;
    }

    public void setTag(int tag) {
        this.tag = tag;
    }

    @Override
    public String toString() {
        return content + "\n" + time.substring(5, 16) + " " + id;
    }

}

NoteActivity

         记事本主界面的Activity

import androidx.annotation.Nullable;
import .AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import androidx.appcompat.widget.SearchView;
import androidx.appcompat.widget.Toolbar;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import java.util.ArrayList;
import java.util.List;

public class NoteActivity extends BaseActivity implements AdapterView.OnItemClickListener {

    FloatingActionButton btn;
    private ListView lv;
    private NoteAdapter adapter;
    private List<Note> noteList = new ArrayList<Note>();
    private Context context = this;
    private Toolbar myToolbar;
    final String TAG = "tag";
    private NoteDatabase dbHelper;
    private Menu menu;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_note);
        btn = (FloatingActionButton) findViewById(.fab);
        lv = (ListView) findViewById();
        myToolbar = findViewById(.myToolbar);
        adapter = new NoteAdapter(getApplicationContext(), noteList);
        refreshListView();
        lv.setAdapter(adapter);
        setSupportActionBar(myToolbar);
        getSupportActionBar().setHomeButtonEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true); //设置toolbar取代actionbar
        lv.setOnItemClickListener(this);
        myToolbar.setNavigationIcon(R.drawable.ic_arrow_back_black_24dp);
        myToolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(NoteActivity.this, SliderActivity.class));
            }
        });
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(NoteActivity.this, EditNoteActivity.class);
                intent.putExtra("mode", 4);
                startActivityForResult(intent, 0);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable 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);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);

        //search setting
        MenuItem mSearch = menu.findItem(.action_search);
        SearchView mSearchView = (SearchView) mSearch.getActionView();
        mSearchView.setQueryHint("Search");
        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);
    }

    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();
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        switch (parent.getId()) {
            case :
                Note curNote = (Note) parent.getItemAtPosition(position);
                Intent intent = new Intent(NoteActivity.this, EditNoteActivity.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;
        }
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case .menu_clear:
                new AlertDialog.Builder(NoteActivity.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(, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                }).create().show();
                break;
        }
        return super.onOptionsItemSelected(item);
    }
}

NoteAdapter

        适配器为主界面列表绑定数据

import android.content.Context;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;
import android.text.TextUtils;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Filter;
import android.widget.Filterable;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;

public class NoteAdapter extends BaseAdapter implements Filterable {
    private Context mContext;
    private List<Note> backList;//用来备份原始数据
    private List<Note> noteList;//这个数据是会改变的，所以要有个变量来备份一下原始数据
    private MyFilter mFilter;

    public NoteAdapter(Context mContext, List<Note> noteList) {
        this.mContext = mContext;
        this.noteList = noteList;
        backList = noteList;
    }

    @Override
    public int getCount() {
        return noteList.size();
    }

    @Override
    public Object getItem(int position) {
        return noteList.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(mContext);
        mContext.setTheme(R.style.DayTheme);
        View v = View.inflate(mContext, R.layout.note_layout, null);
        TextView tv_content = (TextView) v.findViewById(.tv_content);
        TextView tv_time = (TextView) v.findViewById(.tv_time);
        //Set text for TextView
        String allText = noteList.get(position).getContent();
        /*if (sharedPreferences.getBoolean("noteTitle" ,true))
            tv_content.setText(allText.split("\n")[0]);*/
        tv_content.setText(allText);
        tv_time.setText(noteList.get(position).getTime());
        //Save note id to tag
        v.setTag(noteList.get(position).getId());
        return v;
    }

    @Override
    public Filter getFilter() {
        if (mFilter == null) {
            mFilter = new MyFilter();
        }
        return mFilter;
    }

    class MyFilter extends Filter {
        //在performFiltering(CharSequence charSequence)这个方法中定义过滤规则
        @Override
        protected FilterResults performFiltering(CharSequence charSequence) {
            FilterResults result = new FilterResults();
            List<Note> list;
            if (TextUtils.isEmpty(charSequence)) {//当过滤的关键字为空的时候，我们则显示所有的数据
                list = backList;
            } else {//否则把符合条件的数据对象添加到集合中
                list = new ArrayList<>();
                for (Note note : backList) {
                    if (note.getContent().contains(charSequence)) {
                        list.add(note);
                    }
                }
            }
            result.values = list; //将得到的集合保存到FilterResults的value变量中
            result.count = list.size();//将集合的大小保存到FilterResults的count变量中
            return result;
        }

        //在publishResults方法中告诉适配器更新界面
        @Override
        protected void publishResults(CharSequence charSequence, FilterResults filterResults) {
            noteList = (List<Note>) filterResults.values;
            if (filterResults.count > 0) {
                notifyDataSetChanged();//通知数据发生了改变
            } else {
                notifyDataSetInvalidated();//通知数据失效
            }
        }
    }
}

NoteDatabase

        用到的是SQLite数据库，Android自带了一种轻量级数据库，使用非常方便。

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) {
    }
}

EditNoteActivity

        编辑页面的Activity

import .AlertDialog;
import androidx.appcompat.widget.Toolbar;
import android.content.DialogInterface;
import android.content.Intent;
import android.view.KeyEvent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import java.text.SimpleDateFormat;
import java.util.Date;

public class EditNoteActivity extends BaseActivity {

    private 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.activity_edit_note);
        myToolbar = findViewById(.my_Toolbar);
        setSupportActionBar(myToolbar);
        getSupportActionBar().setHomeButtonEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true); //设置toolbar取代actionbar
        myToolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                autoSetMessage();
                setResult(RESULT_OK, intent);
                finish();
            }
        });
        et = findViewById(.et);
        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());
        }
    }

    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 String dateToStr() {
        Date date = new Date();
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        return simpleDateFormat.format(date);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case .delete:
                new AlertDialog.Builder(EditNoteActivity.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(, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                }).create().show();
                break;
        }
        return super.onOptionsItemSelected(item);
    }

    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);
            }
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.edit_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }
}

CRUD

        对SQLite数据库增删改查操作，增加、删除、修改、查询记事信息

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;
    }

    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;
    }

    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())});
    }

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

}

结果