Android 开发简单记事本程序

    简单介绍一下功能：简单记事本只能添加文字内容，首页用ListView显示所有保存的事项和保存的时间，添加页面添加内容，点击首页的ListView可以查看内容，删除内容。

    先看一下运行效果：

先建立数据库：

package com.engineer.shizhibin.note;

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

public class NoteDb 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 NoteDb(Context context) {
        super(context, "notes", null,1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql ="create table "+TABLE_NAME+" ( "+ID+" integer primary key AUTOINCREMENT, "+CONTENT
                +" TEXT NOT NULL, "+TIME+" TEXT NOT NULL )";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}

然后是MainActivity：

    有显示目录的ListView，和添加按钮。他们都要设置点击监听事件。点击添加 跳转到添加文字的activity 点击ListView跳转到Show Activity。

onResume() 在 Activity 从 Pause 状态转换到 Active 状态时被调用。在这个方法中访问SQLite数据库，通过Adapter将条目的内容和添加时间显示在ListView中。看代码：

package com.engineer.shizhibin.note;

import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListView;

public class MainActivity extends AppCompatActivity {
   private Button mButton;
   private ListView mList;
   private Intent mIntent;
   private MyAdapter mAdapter;
   private NoteDb mNotedb;
   private Cursor cursor;
   private SQLiteDatabase dbreader;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mList = (ListView) this.findViewById(R.id.list);
        mNotedb = new NoteDb(this);
        dbreader = mNotedb.getReadableDatabase();
        mList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView adapterView, View view, int i, long l) {
                cursor.moveToPosition(i);
                Intent intent = new Intent(MainActivity.this,ShowContent.class);
                intent.putExtra(NoteDb.ID,cursor.getInt(cursor.getColumnIndex(NoteDb.ID)));
                intent.putExtra(NoteDb.CONTENT,cursor.getString(cursor.getColumnIndex(NoteDb.CONTENT)));
                intent.putExtra(NoteDb.TIME,cursor.getString(cursor.getColumnIndex(NoteDb.TIME)));
                startActivity(intent);
            }
        });
    }

    public void add(View v) {
        mIntent = new Intent(MainActivity.this,AddContent.class);
        startActivity(mIntent);
    }
    public void selectDb() {
        cursor = dbreader.query
                (NoteDb.TABLE_NAME,null,null,null,null,null,null);
        mAdapter = new MyAdapter(this,cursor);
        mList.setAdapter(mAdapter);
    }

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

    为了方便程序扩展，以后有可能添加图片、视频内容 我用了自定义的Adapter 继承自BadeAdapter：

package com.engineer.shizhibin.note;

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

public class MyAdapter extends BaseAdapter {
    private Context mContext;
    private Cursor mCursor;
    private LinearLayout mLayout;
    public MyAdapter(Context mContext,Cursor mCursor) {
        this.mContext = mContext;
        this.mCursor = mCursor;
    }

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

    @Override
    public Object getItem(int position) {
        return mCursor.getPosition();
    }

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

    @Override
    public View getView(int position, View view, ViewGroup viewGroup) {
        LayoutInflater inflater = LayoutInflater.from(mContext);
        mLayout = (LinearLayout) inflater.inflate(R.layout.item,null);
        TextView content = (TextView) mLayout.findViewById(R.id.list_content);
        TextView time = (TextView) mLayout.findViewById(R.id.list_time);
        mCursor.moveToPosition(position);
        String dbcontext = mCursor.getString(mCursor.getColumnIndex("content"));
        String dbtime = mCursor.getString(mCursor.getColumnIndex("time"));
        content.setText(dbcontext);
        time.setText(dbtime);
        return mLayout;
    }
}

添加条目，向数据中添加数据用ContentValues以键值对的方式 非常方便：

package com.engineer.shizhibin.note;

import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

import java.text.SimpleDateFormat;
import java.util.Date;

public class AddContent extends AppCompatActivity {
    private EditText mEt;
    private NoteDb mDb;
    private SQLiteDatabase mSqldb;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_content);
        mEt = (EditText) this.findViewById(R.id.text);
        mDb = new NoteDb(this);
        mSqldb = mDb.getWritableDatabase();
    }
    public void save(View v) {
        DbAdd();
        finish();
    }
    public void cancle(View v) {
        mEt.setText("");
        finish();
    }
    public void DbAdd() {
        ContentValues cv = new ContentValues();
        cv.put(NoteDb.CONTENT,mEt.getText().toString());
        cv.put(NoteDb.TIME,getTime());
        mSqldb.insert(NoteDb.TABLE_NAME,null,cv);
    }
    public String getTime() {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
        Date date = new Date();
        String str = sdf.format(date);
        return str;
    }
}

查看条目：

package com.engineer.shizhibin.note;

import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class ShowContent extends AppCompatActivity {
    private TextView mTextview;
    private TextView time;
    private NoteDb mDb;
    private SQLiteDatabase mSql;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_show_content);
        mTextview = (TextView)this.findViewById(R.id.showtext);
        time = (TextView)this.findViewById(R.id.showtime);
        mDb = new NoteDb(this);
        mSql = mDb.getWritableDatabase();
        mTextview.setText(getIntent().getStringExtra(NoteDb.CONTENT));
        time.setText(getIntent().getStringExtra(NoteDb.TIME));
    }
    public void delete(View v) {
        int id = getIntent().getIntExtra(NoteDb.ID,0);
        mSql.delete(NoteDb.TABLE_NAME," _id = " + id,null);
        finish();

    }
    public void goBack(View v) {
        finish();
    }
}

MainActivity布局：

添加Activity布局：

查看页布局：

ListView布局